diff --git a/rtgui/batchqueue.cc b/rtgui/batchqueue.cc
index fbe2be4c6c..7bd53c4446 100644
--- a/rtgui/batchqueue.cc
+++ b/rtgui/batchqueue.cc
@@ -85,6 +85,8 @@ BatchQueue::BatchQueue (FileCatalog* aFileCatalog) : processing(nullptr), fileCa
 
 BatchQueue::~BatchQueue ()
 {
+    idle_register.destroy();
+
     MYWRITERLOCK(l, entryRW);
 
     // The listener merges parameters with old values, so delete afterwards
@@ -937,7 +939,7 @@ void BatchQueue::notifyListener (bool queueEmptied)
         }
         params->queueEmptied = queueEmptied;
         params->queueError = false;
-        add_idle (bqnotifylistenerUI, params);
+        idle_register.add(bqnotifylistenerUI, params);
     }
 }
 
@@ -967,6 +969,6 @@ void BatchQueue::error (Glib::ustring msg)
         params->queueEmptied = false;
         params->queueError = true;
         params->queueErrorMessage = msg;
-        add_idle (bqnotifylistenerUI, params);
+        idle_register.add(bqnotifylistenerUI, params);
     }
 }
diff --git a/rtgui/batchqueue.h b/rtgui/batchqueue.h
index f7376680b4..68373838ed 100644
--- a/rtgui/batchqueue.h
+++ b/rtgui/batchqueue.h
@@ -36,37 +36,12 @@ class BatchQueueListener
 };
 
 class FileCatalog;
-class BatchQueue  : public ThumbBrowserBase,
+
+class BatchQueue final :
+    public ThumbBrowserBase,
     public rtengine::BatchProcessingListener,
     public LWButtonListener
 {
-
-protected:
-    int getMaxThumbnailHeight() const;
-    void saveThumbnailHeight (int height);
-    int  getThumbnailHeight ();
-
-    BatchQueueEntry* processing;  // holds the currently processed image
-    FileCatalog* fileCatalog;
-    int sequence; // holds the current sequence index
-
-    Glib::ustring nameTemplate;
-
-    MyImageMenuItem* cancel;
-    MyImageMenuItem* head;
-    MyImageMenuItem* tail;
-    Gtk::MenuItem* selall;
-    Gtk::MenuItem* open;
-    Glib::RefPtr<Gtk::AccelGroup> pmaccelgroup;
-    Gtk::Menu pmenu;
-
-    BatchQueueListener* listener;
-
-    Glib::ustring autoCompleteFileName (const Glib::ustring& fileName, const Glib::ustring& format);
-    Glib::ustring getTempFilenameForParams( const Glib::ustring &filename );
-    bool saveBatchQueue ();
-    void notifyListener (bool queueEmptied);
-
 public:
     explicit BatchQueue (FileCatalog* aFileCatalog);
     ~BatchQueue ();
@@ -106,6 +81,34 @@ class BatchQueue  : public ThumbBrowserBase,
 
     static Glib::ustring calcAutoFileNameBase (const Glib::ustring& origFileName, int sequence = 0);
     static int calcMaxThumbnailHeight();
+
+protected:
+    int getMaxThumbnailHeight() const;
+    void saveThumbnailHeight (int height);
+    int  getThumbnailHeight ();
+
+    Glib::ustring autoCompleteFileName (const Glib::ustring& fileName, const Glib::ustring& format);
+    Glib::ustring getTempFilenameForParams( const Glib::ustring &filename );
+    bool saveBatchQueue ();
+    void notifyListener (bool queueEmptied);
+
+    BatchQueueEntry* processing;  // holds the currently processed image
+    FileCatalog* fileCatalog;
+    int sequence; // holds the current sequence index
+
+    Glib::ustring nameTemplate;
+
+    MyImageMenuItem* cancel;
+    MyImageMenuItem* head;
+    MyImageMenuItem* tail;
+    Gtk::MenuItem* selall;
+    Gtk::MenuItem* open;
+    Glib::RefPtr<Gtk::AccelGroup> pmaccelgroup;
+    Gtk::Menu pmenu;
+
+    BatchQueueListener* listener;
+
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/blackwhite.cc b/rtgui/blackwhite.cc
index dab459a140..67dd9f64a2 100644
--- a/rtgui/blackwhite.cc
+++ b/rtgui/blackwhite.cc
@@ -364,23 +364,25 @@ BlackWhite::BlackWhite (): FoldableToolPanel(this, "blackwhite", M("TP_BWMIX_LAB
 }
 BlackWhite::~BlackWhite ()
 {
+    idle_register.destroy();
+
     delete luminanceCEG;
     delete beforeCurveCEG;
     delete afterCurveCEG;
 }
 
-int BWChangedUI (void* data)
-{
-    (static_cast<BlackWhite*>(data))->BWComputed_ ();
-    return 0;
-}
-
 void BlackWhite::BWChanged  (double redbw, double greenbw, double bluebw)
 {
     nextredbw = redbw;
     nextgreenbw = greenbw;
     nextbluebw = bluebw;
-    add_idle (BWChangedUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<BlackWhite*>(data)->BWComputed_();
+        return FALSE;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool BlackWhite::BWComputed_ ()
diff --git a/rtgui/blackwhite.h b/rtgui/blackwhite.h
index e38258b044..5f0ffec44d 100644
--- a/rtgui/blackwhite.h
+++ b/rtgui/blackwhite.h
@@ -28,10 +28,64 @@
 #include "mycurve.h"
 #include "colorprovider.h"
 
-class BlackWhite : public ToolParamBlock, public AdjusterListener, public FoldableToolPanel, public rtengine::AutoBWListener, public CurveListener, public ColorProvider
+class BlackWhite final :
+    public ToolParamBlock,
+    public AdjusterListener,
+    public FoldableToolPanel,
+    public rtengine::AutoBWListener,
+    public CurveListener,
+    public ColorProvider
 {
+public:
+
+    BlackWhite ();
+    ~BlackWhite ();
+
+    void read            (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
+    void write           (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
+    void setDefaults     (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
+    void setBatchMode    (bool batchMode);
+    void autoOpenCurve   ();
+    void setEditProvider (EditDataProvider *provider);
+
+    void autoch_toggled  ();
+    void neutral_pressed ();
+
+    void updateRGBLabel      ();
+    void adjusterChanged     (Adjuster* a, double newval);
+    void setAdjusterBehavior (bool bwadd, bool bwgadd);
+    void trimValues          (rtengine::procparams::ProcParams* pp);
+    void enabledcc_toggled   ();
+    void enabledChanged      ();
+    void methodChanged       ();
+    void filterChanged       ();
+    void settingChanged      ();
+    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
+    void BWChanged           (double redbw, double greenbw, double bluebw);
+    bool BWComputed_         ();
+    void curveChanged        (CurveEditor* ce);
+    void curveMode1Changed   ();
+    bool curveMode1Changed_  ();
+    void curveMode1Changed2  ();
+    bool curveMode1Changed2_ ();
+    void algoChanged         ();
+
+    Glib::ustring getSettingString ();
+    Glib::ustring getFilterString  ();
+    Glib::ustring getalgoString  ();
+
+private:
+    void showLuminance();
+    void hideLuminance();
+    void showFilter();
+    void hideFilter();
+    void showEnabledCC();
+    void hideEnabledCC();
+    void showMixer(int nChannels, bool RGBIsSensitive = true);
+    void hideMixer();
+    void showGamma();
+    void hideGamma();
 
-protected:
     FlatCurveEditor*     luminanceCurve;
     Gtk::HSeparator*     luminanceSep;
     CurveEditorGroup*    luminanceCEG;
@@ -85,55 +139,7 @@ class BlackWhite : public ToolParamBlock, public AdjusterListener, public Foldab
     double nextgreenbw;
     double nextbluebw;
 
-    void showLuminance();
-    void hideLuminance();
-    void showFilter();
-    void hideFilter();
-    void showEnabledCC();
-    void hideEnabledCC();
-    void showMixer(int nChannels, bool RGBIsSensitive = true);
-    void hideMixer();
-    void showGamma();
-    void hideGamma();
-
-public:
-
-    BlackWhite ();
-    ~BlackWhite ();
-
-    void read            (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
-    void write           (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
-    void setDefaults     (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
-    void setBatchMode    (bool batchMode);
-    void autoOpenCurve   ();
-    void setEditProvider (EditDataProvider *provider);
-
-    void autoch_toggled  ();
-    void neutral_pressed ();
-
-    void updateRGBLabel      ();
-    void adjusterChanged     (Adjuster* a, double newval);
-    void setAdjusterBehavior (bool bwadd, bool bwgadd);
-    void trimValues          (rtengine::procparams::ProcParams* pp);
-    void enabledcc_toggled   ();
-    void enabledChanged      ();
-    void methodChanged       ();
-    void filterChanged       ();
-    void settingChanged      ();
-    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
-    void BWChanged           (double redbw, double greenbw, double bluebw);
-    bool BWComputed_         ();
-    void curveChanged        (CurveEditor* ce);
-    void curveMode1Changed   ();
-    bool curveMode1Changed_  ();
-    void curveMode1Changed2  ();
-    bool curveMode1Changed2_ ();
-    void algoChanged         ();
-
-    Glib::ustring getSettingString ();
-    Glib::ustring getFilterString  ();
-    Glib::ustring getalgoString  ();
-
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/cachemanager.cc b/rtgui/cachemanager.cc
index 7421711eb0..68ab74d950 100644
--- a/rtgui/cachemanager.cc
+++ b/rtgui/cachemanager.cc
@@ -19,6 +19,7 @@
 #include "cachemanager.h"
 
 #include <memory>
+#include <iostream>
 
 #include <glib/gstdio.h>
 #include <giomm.h>
diff --git a/rtgui/colorappearance.cc b/rtgui/colorappearance.cc
index 528047a22c..a198dd1f56 100644
--- a/rtgui/colorappearance.cc
+++ b/rtgui/colorappearance.cc
@@ -424,6 +424,8 @@ ColorAppearance::ColorAppearance () : FoldableToolPanel(this, "colorappearance",
 
 ColorAppearance::~ColorAppearance ()
 {
+    idle_register.destroy();
+
     delete curveEditorG;
     delete curveEditorG2;
     delete curveEditorG3;
@@ -1002,15 +1004,17 @@ void ColorAppearance::setDefaults (const ProcParams* defParams, const ParamsEdit
 
     }
 }
-int autoCamChangedUI (void* data)
-{
-    (static_cast<ColorAppearance*>(data))->autoCamComputed_ ();
-    return 0;
-}
+
 void ColorAppearance::autoCamChanged (double ccam)
 {
     nextCcam = ccam;
-    add_idle (autoCamChangedUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<ColorAppearance*>(data)->autoCamComputed_();
+        return FALSE;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool ColorAppearance::autoCamComputed_ ()
@@ -1023,15 +1027,17 @@ bool ColorAppearance::autoCamComputed_ ()
 
     return false;
 }
-int adapCamChangedUI (void* data)
-{
-    (static_cast<ColorAppearance*>(data))->adapCamComputed_ ();
-    return 0;
-}
+
 void ColorAppearance::adapCamChanged (double cadap)
 {
     nextCadap = cadap;
-    add_idle (adapCamChangedUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<ColorAppearance*>(data)->adapCamComputed_();
+        return FALSE;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool ColorAppearance::adapCamComputed_ ()
diff --git a/rtgui/colorappearance.h b/rtgui/colorappearance.h
index 1560e275e7..e7b7e072d8 100644
--- a/rtgui/colorappearance.h
+++ b/rtgui/colorappearance.h
@@ -28,10 +28,61 @@
 #include "guiutils.h"
 #include "colorprovider.h"
 
-class ColorAppearance : public ToolParamBlock, public AdjusterListener, public FoldableToolPanel, public rtengine::AutoCamListener, public CurveListener,  public ColorProvider
+class ColorAppearance final :
+    public ToolParamBlock,
+    public AdjusterListener,
+    public FoldableToolPanel,
+    public rtengine::AutoCamListener,
+    public CurveListener,
+    public ColorProvider
 {
+public:
+    ColorAppearance ();
+    ~ColorAppearance ();
+
+    void read           (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
+    void write          (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
+    void setDefaults    (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
+    void setBatchMode   (bool batchMode);
+    void adjusterChanged     (Adjuster* a, double newval);
+    void adjusterAutoToggled (Adjuster* a, bool newval);
+//    void adjusterAdapToggled (Adjuster* a, bool newval);
+    void enabledChanged      ();
+    void surroundChanged     ();
+    void wbmodelChanged      ();
+    void algoChanged         ();
+    void surrsource_toggled  ();
+    void gamut_toggled       ();
+//   void badpix_toggled       ();
+    void datacie_toggled     ();
+    void tonecie_toggled     ();
+//    void sharpcie_toggled     ();
+    void autoCamChanged (double ccam);
+    bool autoCamComputed_ ();
+    void adapCamChanged (double cadap);
+    bool adapCamComputed_ ();
+
+    void curveChanged        (CurveEditor* ce);
+    void curveMode1Changed   ();
+    bool curveMode1Changed_  ();
+    void curveMode2Changed   ();
+    bool curveMode2Changed_  ();
+    void curveMode3Changed   ();
+    bool curveMode3Changed_  ();
+
+    void expandCurve         (bool isExpanded);
+    bool isCurveExpanded     ();
+    void autoOpenCurve       ();
+
+    void setAdjusterBehavior (bool degreeadd, bool adapscenadd, bool adaplumadd, bool badpixsladd, bool jlightadd, bool chromaadd, bool contrastadd, bool rstprotectionadd, bool qbrightadd, bool qcontrastadd, bool schromaadd, bool mchromaadd, bool colorhadd);
+    void trimValues          (rtengine::procparams::ProcParams* pp);
+    void updateCurveBackgroundHistogram (LUTu & histToneCurve, LUTu & histLCurve, LUTu & histCCurve,/* LUTu & histCLurve, LUTu & histLLCurve,*/ LUTu & histLCAM, LUTu & histCCAM, LUTu & histRed, LUTu & histGreen, LUTu & histBlue, LUTu & histLuma, LUTu & histLRETI);
+    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller *caller);
+
+private:
+    bool bgTTipQuery(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);
+    bool srTTipQuery(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);
 
-protected:
     Glib::RefPtr<Gtk::Tooltip> bgTTips;
     Glib::RefPtr<Gtk::Tooltip> srTTips;
     Glib::RefPtr<Gdk::Pixbuf> bgPixbuf;
@@ -83,56 +134,10 @@ class ColorAppearance : public ToolParamBlock, public AdjusterListener, public F
     bool lastAutoAdapscen;
     bool lastsurr;
     bool lastgamut;
-//  bool lastbadpix;
     bool lastdatacie;
     bool lasttonecie;
-// bool lastsharpcie;
-    bool bgTTipQuery(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);
-    bool srTTipQuery(int x, int y, bool keyboard_tooltip, const Glib::RefPtr<Gtk::Tooltip>& tooltip);
-
-public:
-
-    ColorAppearance ();
-    ~ColorAppearance ();
 
-    void read           (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
-    void write          (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
-    void setDefaults    (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
-    void setBatchMode   (bool batchMode);
-    void adjusterChanged     (Adjuster* a, double newval);
-    void adjusterAutoToggled (Adjuster* a, bool newval);
-//    void adjusterAdapToggled (Adjuster* a, bool newval);
-    void enabledChanged      ();
-    void surroundChanged     ();
-    void wbmodelChanged      ();
-    void algoChanged         ();
-    void surrsource_toggled  ();
-    void gamut_toggled       ();
-//   void badpix_toggled       ();
-    void datacie_toggled     ();
-    void tonecie_toggled     ();
-//    void sharpcie_toggled     ();
-    void autoCamChanged (double ccam);
-    bool autoCamComputed_ ();
-    void adapCamChanged (double cadap);
-    bool adapCamComputed_ ();
-
-    void curveChanged        (CurveEditor* ce);
-    void curveMode1Changed   ();
-    bool curveMode1Changed_  ();
-    void curveMode2Changed   ();
-    bool curveMode2Changed_  ();
-    void curveMode3Changed   ();
-    bool curveMode3Changed_  ();
-
-    void expandCurve         (bool isExpanded);
-    bool isCurveExpanded     ();
-    void autoOpenCurve       ();
-
-    void setAdjusterBehavior (bool degreeadd, bool adapscenadd, bool adaplumadd, bool badpixsladd, bool jlightadd, bool chromaadd, bool contrastadd, bool rstprotectionadd, bool qbrightadd, bool qcontrastadd, bool schromaadd, bool mchromaadd, bool colorhadd);
-    void trimValues          (rtengine::procparams::ProcParams* pp);
-    void updateCurveBackgroundHistogram (LUTu & histToneCurve, LUTu & histLCurve, LUTu & histCCurve,/* LUTu & histCLurve, LUTu & histLLCurve,*/ LUTu & histLCAM, LUTu & histCCAM, LUTu & histRed, LUTu & histGreen, LUTu & histBlue, LUTu & histLuma, LUTu & histLRETI);
-    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller *caller);
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/colortoning.cc b/rtgui/colortoning.cc
index ceec0092f7..d471ef787a 100644
--- a/rtgui/colortoning.cc
+++ b/rtgui/colortoning.cc
@@ -324,6 +324,8 @@ ColorToning::ColorToning () : FoldableToolPanel(this, "colortoning", M("TP_COLOR
 
 ColorToning::~ColorToning()
 {
+    idle_register.destroy();
+
     delete colorCurveEditorG;
     delete opacityCurveEditorG;
     delete clCurveEditorG;
@@ -650,19 +652,18 @@ void ColorToning::adjusterChanged (ThresholdAdjuster* a, double newBottom, doubl
                                 Glib::ustring::compose(Glib::ustring(M("TP_COLORTONING_HUE") + ": %1" + "\n" + M("TP_COLORTONING_STRENGTH") + ": %2"), int(newTop), int(newBottom)));
 }
 
-int CTChanged_UI (void* data)
-{
-    (static_cast<ColorToning*>(data))->CTComp_ ();
-    return 0;
-}
-
-
 void ColorToning::autoColorTonChanged(int bwct, int satthres, int satprot)
 {
     nextbw = bwct;
     nextsatth = satthres;
     nextsatpr = satprot;
-    add_idle (CTChanged_UI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<ColorToning*>(data)->CTComp_();
+        return FALSE;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool ColorToning::CTComp_ ()
diff --git a/rtgui/colortoning.h b/rtgui/colortoning.h
index e344473019..7f1290bf61 100644
--- a/rtgui/colortoning.h
+++ b/rtgui/colortoning.h
@@ -13,12 +13,43 @@
 #include "thresholdadjuster.h"
 #include "colorprovider.h"
 
-class ColorToning : public ToolParamBlock, public FoldableToolPanel,  public rtengine::AutoColorTonListener, public CurveListener, public ColorProvider,
-    public ThresholdAdjusterListener, public AdjusterListener
+class ColorToning final :
+    public ToolParamBlock,
+    public FoldableToolPanel,
+    public rtengine::AutoColorTonListener,
+    public CurveListener,
+    public ColorProvider,
+    public ThresholdAdjusterListener,
+    public AdjusterListener
 {
+public:
+    ColorToning ();
+    ~ColorToning();
+    void read                  (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
+    void write                 (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
+    void setBatchMode          (bool batchMode);
+    void setDefaults           (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
+    void trimValues            (rtengine::procparams::ProcParams* pp);
+    void adjusterChanged       (Adjuster* a, double newval);
+    void adjusterChanged       (ThresholdAdjuster* a, double newBottom, double newTop);
+    void setAdjusterBehavior   (bool splitAdd, bool satThresholdAdd, bool satOpacityAdd, bool strprotectAdd, bool balanceAdd);
+    void neutral_pressed       ();
+    //void neutralCurves_pressed ();
+    void autoColorTonChanged   (int bwct, int satthres, int satprot);
+    bool CTComp_               ();
+
+    void enabledChanged        ();
+    void curveChanged          (CurveEditor* ce);
+    void autosatChanged        ();
+    void autoOpenCurve         ();
+    void methodChanged         ();
+    void twocolorChanged       (bool changedbymethod);
+    void twoColorChangedByGui  ();
+    void lumamodeChanged       ();
+
+    void colorForValue         (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
 
-protected:
-    //Gtk::HSeparator* splitSep;
+private:
     Gtk::HSeparator* satLimiterSep;
     Gtk::HSeparator* colorSep;
     CurveEditorGroup* colorCurveEditorG;
@@ -57,7 +88,6 @@ class ColorToning : public ToolParamBlock, public FoldableToolPanel,  public rte
     Gtk::Image* irg;
 
     Gtk::Button* neutral;
-    //Gtk::Button* neutralCurves;
     Gtk::HBox* neutrHBox;
     Gtk::HBox* chromaHbox;
     Gtk::Label* chroLabel;
@@ -75,32 +105,7 @@ class ColorToning : public ToolParamBlock, public FoldableToolPanel,  public rte
     bool lastLumamode;
     sigc::connection lumamodeConn;
 
-public:
-    ColorToning ();
-    ~ColorToning();
-    void read                  (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
-    void write                 (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
-    void setBatchMode          (bool batchMode);
-    void setDefaults           (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
-    void trimValues            (rtengine::procparams::ProcParams* pp);
-    void adjusterChanged       (Adjuster* a, double newval);
-    void adjusterChanged       (ThresholdAdjuster* a, double newBottom, double newTop);
-    void setAdjusterBehavior   (bool splitAdd, bool satThresholdAdd, bool satOpacityAdd, bool strprotectAdd, bool balanceAdd);
-    void neutral_pressed       ();
-    //void neutralCurves_pressed ();
-    void autoColorTonChanged   (int bwct, int satthres, int satprot);
-    bool CTComp_               ();
-
-    void enabledChanged        ();
-    void curveChanged          (CurveEditor* ce);
-    void autosatChanged        ();
-    void autoOpenCurve         ();
-    void methodChanged         ();
-    void twocolorChanged       (bool changedbymethod);
-    void twoColorChangedByGui  ();
-    void lumamodeChanged       ();
-
-    void colorForValue         (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/crop.cc b/rtgui/crop.cc
index a69c71ed82..83efb6a37a 100644
--- a/rtgui/crop.cc
+++ b/rtgui/crop.cc
@@ -25,6 +25,9 @@ using namespace rtengine::procparams;
 
 extern Options options;
 
+namespace
+{
+
 class RefreshSpinHelper
 {
 
@@ -35,6 +38,22 @@ class RefreshSpinHelper
         : crop(_crop), notify(_notify) {}
 };
 
+int refreshSpinsUI (void* data)
+{
+    RefreshSpinHelper* rsh = static_cast<RefreshSpinHelper*>(data);
+    rsh->crop->refreshSpins (rsh->notify);
+    delete rsh;
+    return 0;
+}
+
+int notifyListenerUI (void* data)
+{
+    static_cast<Crop*>(data)->notifyListener();
+    return 0;
+}
+
+}
+
 Crop::Crop (): FoldableToolPanel(this, "crop", M("TP_CROP_LABEL"), false, true)
 {
 
@@ -252,6 +271,11 @@ Crop::Crop (): FoldableToolPanel(this, "crop", M("TP_CROP_LABEL"), false, true)
     show_all ();
 }
 
+Crop::~Crop()
+{
+    idle_register.destroy();
+}
+
 void Crop::writeOptions ()
 {
 
@@ -508,32 +532,18 @@ void Crop::enabledChanged ()
     }
 }
 
-int notifyListenerUI (void* data)
-{
-    (static_cast<Crop*>(data))->notifyListener ();
-    return 0;
-}
-
-int refreshSpinsUI (void* data)
-{
-    RefreshSpinHelper* rsh = static_cast<RefreshSpinHelper*>(data);
-    rsh->crop->refreshSpins (rsh->notify);
-    delete rsh;
-    return 0;
-}
-
 void Crop::hFlipCrop ()
 {
 
     nx = maxw - nx - nw;
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::vFlipCrop ()
 {
 
     ny = maxh - ny - nh;
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::rotateCrop (int deg, bool hflip, bool vflip)
@@ -573,7 +583,7 @@ void Crop::rotateCrop (int deg, bool hflip, bool vflip)
     }
 
     lastRotationDeg = deg;
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::positionChanged ()
@@ -587,7 +597,7 @@ void Crop::positionChanged ()
     int W = nw;
     int H = nh;
     cropMoved (X, Y, W, H);
-    add_idle (notifyListenerUI, this);
+    idle_register.add(notifyListenerUI, this);
 }
 
 void Crop::widthChanged ()
@@ -600,7 +610,7 @@ void Crop::widthChanged ()
     int W = (int)w->get_value ();
     int H = nh;
     cropWidth2Resized (X, Y, W, H);
-    add_idle (notifyListenerUI, this);
+    idle_register.add(notifyListenerUI, this);
 }
 
 void Crop::heightChanged ()
@@ -613,7 +623,7 @@ void Crop::heightChanged ()
     int W = nw;
     int H = (int)h->get_value ();
     cropHeight2Resized (X, Y, W, H);
-    add_idle (notifyListenerUI, this);
+    idle_register.add(notifyListenerUI, this);
 }
 
 // Fixed ratio toggle button
@@ -665,7 +675,7 @@ void Crop::adjustCropToRatio()
     }
 
     // This will save the options
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, true));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, true));
 }
 
 void Crop::refreshSize ()
@@ -737,28 +747,28 @@ void Crop::setDimensions (int mw, int mh)
     refreshSize ();
 }
 
-struct setdimparams {
-    Crop* crop;
-    int x;
-    int y;
-};
-
-int sizeChangedUI (void* data)
-{
-    setdimparams* params = static_cast<setdimparams*>(data);
-    params->crop->setDimensions (params->x, params->y);
-    delete params;
-    return 0;
-}
-
 void Crop::sizeChanged (int x, int y, int ow, int oh)
 {
-
-    setdimparams* params = new setdimparams;
-    params->x = x;
-    params->y = y;
-    params->crop = this;
-    add_idle (sizeChangedUI, params);
+    struct Params {
+        Crop* crop;
+        int x;
+        int y;
+    };
+
+    Params* const params = new Params{
+        this,
+        x,
+        y
+    };
+
+    const auto func = [](gpointer data) -> gboolean {
+        Params* const params = static_cast<Params*>(data);
+        params->crop->setDimensions(params->x, params->y);
+        delete params;
+        return FALSE;
+    };
+
+    idle_register.add(func, params);
 }
 
 bool Crop::refreshSpins (bool notify)
@@ -822,7 +832,7 @@ void Crop::cropMoved (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 //  Glib::signal_idle().connect (sigc::mem_fun(*this, &Crop::refreshSpins));
 }
 
@@ -866,7 +876,7 @@ void Crop::cropWidth1Resized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropWidth2Resized (int &X, int &Y, int &W, int &H)
@@ -906,7 +916,7 @@ void Crop::cropWidth2Resized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropHeight1Resized (int &X, int &Y, int &W, int &H)
@@ -949,7 +959,7 @@ void Crop::cropHeight1Resized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropHeight2Resized (int &X, int &Y, int &W, int &H)
@@ -989,7 +999,7 @@ void Crop::cropHeight2Resized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropTopLeftResized (int &X, int &Y, int &W, int &H)
@@ -1031,7 +1041,7 @@ void Crop::cropTopLeftResized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropTopRightResized (int &X, int &Y, int &W, int &H)
@@ -1071,7 +1081,7 @@ void Crop::cropTopRightResized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropBottomLeftResized (int &X, int &Y, int &W, int &H)
@@ -1111,7 +1121,7 @@ void Crop::cropBottomLeftResized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropBottomRightResized (int &X, int &Y, int &W, int &H)
@@ -1148,7 +1158,7 @@ void Crop::cropBottomRightResized (int &X, int &Y, int &W, int &H)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropInit (int &x, int &y, int &w, int &h)
@@ -1266,13 +1276,12 @@ void Crop::cropResized (int &x, int &y, int& x2, int& y2)
     nw = W;
     nh = H;
 
-    add_idle (refreshSpinsUI, new RefreshSpinHelper (this, false));
+    idle_register.add(refreshSpinsUI, new RefreshSpinHelper(this, false));
 }
 
 void Crop::cropManipReady ()
 {
-
-    add_idle (notifyListenerUI, this);
+    idle_register.add(notifyListenerUI, this);
 }
 
 double Crop::getRatio ()
diff --git a/rtgui/crop.h b/rtgui/crop.h
index 077903836f..e0bad8b367 100644
--- a/rtgui/crop.h
+++ b/rtgui/crop.h
@@ -33,44 +33,20 @@ class CropPanelListener
     virtual void cropSelectRequested() = 0;
 };
 
-class CropRatio
-{
-
-public:
+struct CropRatio {
     Glib::ustring label;
     double value;
 };
 
-class Crop : public ToolParamBlock, public CropGUIListener, public FoldableToolPanel, public rtengine::SizeListener
+class Crop final :
+    public ToolParamBlock,
+    public CropGUIListener,
+    public FoldableToolPanel,
+    public rtengine::SizeListener
 {
-protected:
-    Gtk::CheckButton* fixr;
-    MyComboBoxText* ratio;
-    MyComboBoxText* orientation;
-    MyComboBoxText* guide;
-    Gtk::Button* selectCrop;
-    CropPanelListener* clistener;
-    int opt;
-    MySpinButton* x;
-    MySpinButton* y;
-    MySpinButton* w;
-    MySpinButton* h;
-    MySpinButton* ppi;
-    Gtk::Label* sizecm;
-    Gtk::Label* sizein;
-    Gtk::VBox* ppibox;
-    Gtk::VBox* sizebox;
-    int maxw, maxh;
-    double nx, ny;
-    int nw, nh;
-    int lastRotationDeg;
-    sigc::connection xconn, yconn, wconn, hconn, fconn, rconn, oconn, gconn;
-    bool wDirty, hDirty, xDirty, yDirty, lastFixRatio;
-    void adjustCropToRatio();
-    std::vector<CropRatio>   cropratio;
-
 public:
-    Crop ();
+    Crop();
+    ~Crop();
 
     void read           (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
     void write          (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
@@ -116,6 +92,34 @@ class Crop : public ToolParamBlock, public CropGUIListener, public FoldableToolP
     void hFlipCrop          ();
     void vFlipCrop          ();
     void rotateCrop         (int deg, bool hflip, bool vflip);
+
+private:
+    Gtk::CheckButton* fixr;
+    MyComboBoxText* ratio;
+    MyComboBoxText* orientation;
+    MyComboBoxText* guide;
+    Gtk::Button* selectCrop;
+    CropPanelListener* clistener;
+    int opt;
+    MySpinButton* x;
+    MySpinButton* y;
+    MySpinButton* w;
+    MySpinButton* h;
+    MySpinButton* ppi;
+    Gtk::Label* sizecm;
+    Gtk::Label* sizein;
+    Gtk::VBox* ppibox;
+    Gtk::VBox* sizebox;
+    int maxw, maxh;
+    double nx, ny;
+    int nw, nh;
+    int lastRotationDeg;
+    sigc::connection xconn, yconn, wconn, hconn, fconn, rconn, oconn, gconn;
+    bool wDirty, hDirty, xDirty, yDirty, lastFixRatio;
+    void adjustCropToRatio();
+    std::vector<CropRatio>   cropratio;
+
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/crophandler.cc b/rtgui/crophandler.cc
index bb59efe13d..42c6eb7567 100644
--- a/rtgui/crophandler.cc
+++ b/rtgui/crophandler.cc
@@ -38,14 +38,15 @@ CropHandler::CropHandler ()
       displayHandler(nullptr)
 {
 
-    chi = new CropHandlerIdleHelper;
-    chi->destroyed = false;
-    chi->pending = 0;
-    chi->cropHandler = this;
+    idle_helper = new IdleHelper;
+    idle_helper->destroyed = false;
+    idle_helper->pending = 0;
+    idle_helper->cropHandler = this;
 }
 
 CropHandler::~CropHandler ()
 {
+    idle_register.destroy();
 
     if (ipc) {
         ipc->delSizeListener (this);
@@ -61,10 +62,10 @@ CropHandler::~CropHandler ()
 
     cimg.lock ();
 
-    if (chi->pending) {
-        chi->destroyed = true;
+    if (idle_helper->pending) {
+        idle_helper->destroyed = true;
     } else {
-        delete chi;
+        delete idle_helper;
     }
 
     cimg.unlock ();
@@ -292,83 +293,6 @@ void CropHandler::getPosition (int& x, int& y)
 }
 
 
-int createpixbufs (void* data)
-{
-
-    CropHandlerIdleHelper* chi = static_cast<CropHandlerIdleHelper*>(data);
-
-    if (chi->destroyed) {
-        if (chi->pending == 1) {
-            delete chi;
-        } else {
-            chi->pending--;
-        }
-
-        return 0;
-    }
-
-    CropHandler* ch = chi->cropHandler;
-
-    ch->cimg.lock ();
-    ch->cropPixbuf.clear ();
-
-    if (!ch->enabled) {
-        delete [] ch->cropimg;
-        ch->cropimg = nullptr;
-        delete [] ch->cropimgtrue;
-        ch->cropimgtrue = nullptr;
-        ch->cimg.unlock ();
-        return 0;
-    }
-
-    if (ch->cropimg) {
-        if (ch->cix == ch->cropX && ch->ciy == ch->cropY && ch->ciw == ch->cropW && ch->cih == ch->cropH && ch->cis == (ch->zoom >= 1000 ? 1 : ch->zoom)) {
-            // calculate final image size
-            int czoom = ch->zoom < 1000 ? 1000 : ch->zoom;
-            int imw = ch->cropimg_width * czoom / 1000;
-            int imh = ch->cropimg_height * czoom / 1000;
-
-            if (imw > ch->ww) {
-                imw = ch->ww;
-            }
-
-            if (imh > ch->wh) {
-                imh = ch->wh;
-            }
-
-            Glib::RefPtr<Gdk::Pixbuf> tmpPixbuf = Gdk::Pixbuf::create_from_data (ch->cropimg, Gdk::COLORSPACE_RGB, false, 8, ch->cropimg_width, 2 * ch->cropimg_height, 3 * ch->cropimg_width);
-            ch->cropPixbuf = Gdk::Pixbuf::create (Gdk::COLORSPACE_RGB, false, 8, imw, imh);
-            tmpPixbuf->scale (ch->cropPixbuf, 0, 0, imw, imh, 0, 0, czoom / 1000.0, czoom / 1000.0, Gdk::INTERP_NEAREST);
-            tmpPixbuf.clear ();
-
-            Glib::RefPtr<Gdk::Pixbuf> tmpPixbuftrue = Gdk::Pixbuf::create_from_data (ch->cropimgtrue, Gdk::COLORSPACE_RGB, false, 8, ch->cropimg_width, 2 * ch->cropimg_height, 3 * ch->cropimg_width);
-            ch->cropPixbuftrue = Gdk::Pixbuf::create (Gdk::COLORSPACE_RGB, false, 8, imw, imh);
-            tmpPixbuftrue->scale (ch->cropPixbuftrue, 0, 0, imw, imh, 0, 0, czoom / 1000.0, czoom / 1000.0, Gdk::INTERP_NEAREST);
-            tmpPixbuftrue.clear ();
-        }
-
-        delete [] ch->cropimg;
-        ch->cropimg = nullptr;
-        delete [] ch->cropimgtrue;
-        ch->cropimgtrue = nullptr;
-    }
-
-    ch->cimg.unlock ();
-
-    if (ch->displayHandler) {
-        ch->displayHandler->cropImageUpdated ();
-
-        if (ch->initial) {
-            ch->displayHandler->initialImageArrived ();
-            ch->initial = false;
-        }
-    }
-
-    chi->pending--;
-
-    return 0;
-}
-
 void CropHandler::setDetailedCrop (IImage8* im, IImage8* imtrue, rtengine::procparams::ColorManagementParams cmp,
                                    rtengine::procparams::CropParams cp, int ax, int ay, int aw, int ah, int askip)
 {
@@ -408,8 +332,84 @@ void CropHandler::setDetailedCrop (IImage8* im, IImage8* imtrue, rtengine::procp
         ciw = aw;
         cih = ah;
         cis = askip;
-        chi->pending++;
-        add_idle (createpixbufs, chi);
+        idle_helper->pending++;
+
+        const auto func = [](gpointer data) -> gboolean {
+            IdleHelper* const idle_helper = static_cast<IdleHelper*>(data);
+
+            if (idle_helper->destroyed) {
+                if (idle_helper->pending == 1) {
+                    delete idle_helper;
+                } else {
+                    idle_helper->pending--;
+                }
+
+                return FALSE;
+            }
+
+            CropHandler* ch = idle_helper->cropHandler;
+
+            ch->cimg.lock ();
+            ch->cropPixbuf.clear ();
+
+            if (!ch->enabled) {
+                delete [] ch->cropimg;
+                ch->cropimg = nullptr;
+                delete [] ch->cropimgtrue;
+                ch->cropimgtrue = nullptr;
+                ch->cimg.unlock ();
+                return FALSE;
+            }
+
+            if (ch->cropimg) {
+                if (ch->cix == ch->cropX && ch->ciy == ch->cropY && ch->ciw == ch->cropW && ch->cih == ch->cropH && ch->cis == (ch->zoom >= 1000 ? 1 : ch->zoom)) {
+                    // calculate final image size
+                    int czoom = ch->zoom < 1000 ? 1000 : ch->zoom;
+                    int imw = ch->cropimg_width * czoom / 1000;
+                    int imh = ch->cropimg_height * czoom / 1000;
+
+                    if (imw > ch->ww) {
+                        imw = ch->ww;
+                    }
+
+                    if (imh > ch->wh) {
+                        imh = ch->wh;
+                    }
+
+                    Glib::RefPtr<Gdk::Pixbuf> tmpPixbuf = Gdk::Pixbuf::create_from_data (ch->cropimg, Gdk::COLORSPACE_RGB, false, 8, ch->cropimg_width, 2 * ch->cropimg_height, 3 * ch->cropimg_width);
+                    ch->cropPixbuf = Gdk::Pixbuf::create (Gdk::COLORSPACE_RGB, false, 8, imw, imh);
+                    tmpPixbuf->scale (ch->cropPixbuf, 0, 0, imw, imh, 0, 0, czoom / 1000.0, czoom / 1000.0, Gdk::INTERP_NEAREST);
+                    tmpPixbuf.clear ();
+
+                    Glib::RefPtr<Gdk::Pixbuf> tmpPixbuftrue = Gdk::Pixbuf::create_from_data (ch->cropimgtrue, Gdk::COLORSPACE_RGB, false, 8, ch->cropimg_width, 2 * ch->cropimg_height, 3 * ch->cropimg_width);
+                    ch->cropPixbuftrue = Gdk::Pixbuf::create (Gdk::COLORSPACE_RGB, false, 8, imw, imh);
+                    tmpPixbuftrue->scale (ch->cropPixbuftrue, 0, 0, imw, imh, 0, 0, czoom / 1000.0, czoom / 1000.0, Gdk::INTERP_NEAREST);
+                    tmpPixbuftrue.clear ();
+                }
+
+                delete [] ch->cropimg;
+                ch->cropimg = nullptr;
+                delete [] ch->cropimgtrue;
+                ch->cropimgtrue = nullptr;
+            }
+
+            ch->cimg.unlock ();
+
+            if (ch->displayHandler) {
+                ch->displayHandler->cropImageUpdated ();
+
+                if (ch->initial) {
+                    ch->displayHandler->initialImageArrived ();
+                    ch->initial = false;
+                }
+            }
+
+            idle_helper->pending--;
+
+            return FALSE;
+        };
+
+        idle_register.add(func, idle_helper);
     }
 
     cimg.unlock ();
diff --git a/rtgui/crophandler.h b/rtgui/crophandler.h
index 3bf7e58da4..0492aea2a9 100644
--- a/rtgui/crophandler.h
+++ b/rtgui/crophandler.h
@@ -36,56 +36,15 @@ class CropDisplayHandler
     virtual void setDisplayPosition  (int x, int y) {}
 };
 
-class CropHandler;
-struct CropHandlerIdleHelper {
-    CropHandler* cropHandler;
-    bool destroyed;
-    int pending;
-};
-
 /**
  *  This class handle the displayed part of the image, ask for the initial data and process it so it can display it.
  *  Its position on the preview is handled not set by this class but by the CropHandlerListener (i.e. CropWindow) with which it works closely.
  */
-class CropHandler : public rtengine::DetailedCropListener, public rtengine::SizeListener
+class CropHandler final :
+    public rtengine::DetailedCropListener,
+    public rtengine::SizeListener
 {
-
-    friend int createpixbufs (void* data);
-
-protected:
-    int zoom;               // scale factor (e.g. 5 if 1:5 scale) ; if 1:1 scale and bigger, factor is multiplied by 1000  (i.e. 1000 for 1:1 scale, 2000 for 2:1, etc...)
-    int ww, wh;             // size of the crop's canvas on the screen ; might be bigger than the displayed image, but not smaller
-    int imx, imy, imw, imh; // this is a copy of the cropwindow's parameters
-    int cax, cay;           // clamped crop anchor's coordinate, i.e. point of the image that coincide to the center of the display area, expressed in image coordinates; cannot be outside the image's bounds; but if cax==cay==-1, designate the center of the image
-    int cx, cy, cw, ch;     // position and size of the requested crop ; position expressed in image coordinates, so cx and cy might be negative and cw and ch higher than the image's 1:1 size
-    int cropX, cropY, cropW, cropH; // cropPixbuf's displayed area (position and size), i.e. coordinates in 1:1 scale, i.e. cx, cy, cw & ch trimmed to the image's bounds
-    bool enabled;
-    unsigned char* cropimg;
-    unsigned char* cropimgtrue;
-    int cropimg_width, cropimg_height, cix, ciy, ciw, cih, cis;
-    bool initial;
-    bool isLowUpdatePriority;
-
-    rtengine::StagedImageProcessor* ipc;
-    rtengine::DetailedCrop* crop;
-
-    CropDisplayHandler* displayHandler;
-    CropHandlerIdleHelper* chi;
-
-    void    compDim ();
-
 public:
-
-    void    update  ();
-
-
-    rtengine::procparams::CropParams cropParams;
-    rtengine::procparams::ColorManagementParams colorParams;
-    Glib::RefPtr<Gdk::Pixbuf> cropPixbuf;
-    Glib::RefPtr<Gdk::Pixbuf> cropPixbuftrue;
-
-    MyMutex cimg;
-
     CropHandler ();
     ~CropHandler ();
 
@@ -127,6 +86,46 @@ class CropHandler : public rtengine::DetailedCropListener, public rtengine::Size
     bool    getWindow (int& cwx, int& cwy, int& cww, int& cwh, int& cskip);
     // SizeListener interface
     void    sizeChanged  (int w, int h, int ow, int oh);
+
+    void    update  ();
+
+
+    rtengine::procparams::CropParams cropParams;
+    rtengine::procparams::ColorManagementParams colorParams;
+    Glib::RefPtr<Gdk::Pixbuf> cropPixbuf;
+    Glib::RefPtr<Gdk::Pixbuf> cropPixbuftrue;
+
+    MyMutex cimg;
+
+private:
+    struct IdleHelper {
+        CropHandler* cropHandler;
+        bool destroyed;
+        int pending;
+    };
+
+    void    compDim ();
+
+    int zoom;               // scale factor (e.g. 5 if 1:5 scale) ; if 1:1 scale and bigger, factor is multiplied by 1000  (i.e. 1000 for 1:1 scale, 2000 for 2:1, etc...)
+    int ww, wh;             // size of the crop's canvas on the screen ; might be bigger than the displayed image, but not smaller
+    int imx, imy, imw, imh; // this is a copy of the cropwindow's parameters
+    int cax, cay;           // clamped crop anchor's coordinate, i.e. point of the image that coincide to the center of the display area, expressed in image coordinates; cannot be outside the image's bounds; but if cax==cay==-1, designate the center of the image
+    int cx, cy, cw, ch;     // position and size of the requested crop ; position expressed in image coordinates, so cx and cy might be negative and cw and ch higher than the image's 1:1 size
+    int cropX, cropY, cropW, cropH; // cropPixbuf's displayed area (position and size), i.e. coordinates in 1:1 scale, i.e. cx, cy, cw & ch trimmed to the image's bounds
+    bool enabled;
+    unsigned char* cropimg;
+    unsigned char* cropimgtrue;
+    int cropimg_width, cropimg_height, cix, ciy, ciw, cih, cis;
+    bool initial;
+    bool isLowUpdatePriority;
+
+    rtengine::StagedImageProcessor* ipc;
+    rtengine::DetailedCrop* crop;
+
+    CropDisplayHandler* displayHandler;
+    IdleHelper* idle_helper;
+
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/dirbrowser.cc b/rtgui/dirbrowser.cc
index eafaa477a3..7b5adade2e 100644
--- a/rtgui/dirbrowser.cc
+++ b/rtgui/dirbrowser.cc
@@ -18,6 +18,7 @@
  */
 #include "dirbrowser.h"
 
+#include <iostream>
 #include <cstring>
 
 #ifdef WIN32
diff --git a/rtgui/dirpyrdenoise.cc b/rtgui/dirpyrdenoise.cc
index a5611cc455..bd673e5c3f 100644
--- a/rtgui/dirpyrdenoise.cc
+++ b/rtgui/dirpyrdenoise.cc
@@ -327,22 +327,24 @@ DirPyrDenoise::DirPyrDenoise () : FoldableToolPanel(this, "dirpyrdenoise", M("TP
 
 DirPyrDenoise::~DirPyrDenoise ()
 {
+    idle_register.destroy();
+
     delete NoiscurveEditorG;
     delete CCcurveEditorG;
-
-}
-int chromaChangedUI (void* data)
-{
-    (static_cast<DirPyrDenoise*>(data))->chromaComputed_ ();
-    return 0;
 }
+
 void DirPyrDenoise::chromaChanged (double autchroma, double autred, double autblue)
 {
     nextchroma = autchroma;
-//  printf("CHROM=%f\n",nextchroma);
     nextred = autred;
     nextblue = autblue;
-    add_idle(chromaChangedUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<DirPyrDenoise*>(data)->chromaComputed_();
+        return false;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool DirPyrDenoise::chromaComputed_ ()
@@ -356,12 +358,6 @@ bool DirPyrDenoise::chromaComputed_ ()
     updateNoiseLabel ();
     return false;
 }
-int TilePrevChangedUI (void* data)
-{
-    (static_cast<DirPyrDenoise*>(data))->TilePrevComputed_ ();
-    return 0;
-}
-
 
 void DirPyrDenoise::noiseTilePrev (int tileX, int tileY, int prevX, int prevY, int sizeT, int sizeP)
 {
@@ -372,10 +368,14 @@ void DirPyrDenoise::noiseTilePrev (int tileX, int tileY, int prevX, int prevY, i
     nextsizeT = sizeT;
     nextsizeP = sizeP;
 
-    add_idle(TilePrevChangedUI, this);
-
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<DirPyrDenoise*>(data)->TilePrevComputed_();
+        return false;
+    };
 
+    idle_register.add(func, this);
 }
+
 bool DirPyrDenoise::TilePrevComputed_ ()
 {
 
@@ -385,6 +385,7 @@ bool DirPyrDenoise::TilePrevComputed_ ()
     updatePrevLabel ();
     return false;
 }
+
 void DirPyrDenoise::updateTileLabel ()
 {
     if (!batchMode) {
@@ -422,19 +423,17 @@ void DirPyrDenoise::updatePrevLabel ()
     }
 }
 
-
-int noiseChangedUI (void* data)
-{
-    (static_cast<DirPyrDenoise*>(data))->noiseComputed_ ();
-    return 0;
-}
-
-
 void DirPyrDenoise::noiseChanged (double nresid, double highresid)
 {
     nextnresid = nresid;
     nexthighresid = highresid;
-    add_idle(noiseChangedUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<DirPyrDenoise*>(data)->noiseComputed_();
+        return false;
+    };
+
+    idle_register.add(func, this);
 }
 
 bool DirPyrDenoise::noiseComputed_ ()
diff --git a/rtgui/dirpyrdenoise.h b/rtgui/dirpyrdenoise.h
index e81bf263e4..9745b374b2 100644
--- a/rtgui/dirpyrdenoise.h
+++ b/rtgui/dirpyrdenoise.h
@@ -28,10 +28,58 @@
 #include "guiutils.h"
 #include "options.h"
 
-class DirPyrDenoise : public ToolParamBlock, public AdjusterListener, public FoldableToolPanel, public rtengine::AutoChromaListener, public CurveListener, public ColorProvider
+class DirPyrDenoise final :
+    public ToolParamBlock,
+    public AdjusterListener,
+    public FoldableToolPanel,
+    public rtengine::AutoChromaListener,
+    public CurveListener,
+    public ColorProvider
 {
+public:
+    DirPyrDenoise ();
+    ~DirPyrDenoise ();
+
+    void read           (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
+    void write          (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
+    void setDefaults    (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
+    void setBatchMode   (bool batchMode);
+    void curveChanged   (CurveEditor* ce);
+    void setEditProvider     (EditDataProvider *provider);
+    void autoOpenCurve  ();
 
-protected:
+    void adjusterChanged (Adjuster* a, double newval);
+    void enabledChanged  ();
+    void enhanceChanged  ();
+    void medianChanged  ();
+    void autochromaChanged  ();
+    void chromaChanged (double autchroma, double autred, double autblue);
+    bool chromaComputed_ ();
+    void noiseChanged (double nresid, double highresid);
+    bool noiseComputed_ ();
+    void noiseTilePrev (int tileX, int tileY, int prevX, int prevY, int sizeT, int sizeP);
+    bool TilePrevComputed_ ();
+
+//    void perform_toggled  ();
+    void updateNoiseLabel      ();
+    void LmethodChanged      ();
+    void CmethodChanged      ();
+    void C2methodChanged      ();
+    void updateTileLabel      ();
+    void updatePrevLabel      ();
+
+    void dmethodChanged      ();
+    void medmethodChanged      ();
+    void methodmedChanged      ();
+    void rgbmethodChanged      ();
+    void smethodChanged      ();
+    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
+
+    void setAdjusterBehavior (bool lumaadd, bool lumdetadd, bool chromaadd, bool chromaredadd, bool chromablueadd, bool gammaadd, bool passesadd);
+    void trimValues          (rtengine::procparams::ProcParams* pp);
+    Glib::ustring getSettingString ();
+
+private:
     CurveEditorGroup* NoiscurveEditorG;
     CurveEditorGroup* CCcurveEditorG;
     Adjuster* luma;
@@ -92,50 +140,7 @@ class DirPyrDenoise : public ToolParamBlock, public AdjusterListener, public Fol
     int nextsizeT;
     int nextsizeP;
 
-public:
-
-    DirPyrDenoise ();
-    ~DirPyrDenoise ();
-
-    void read           (const rtengine::procparams::ProcParams* pp, const ParamsEdited* pedited = nullptr);
-    void write          (rtengine::procparams::ProcParams* pp, ParamsEdited* pedited = nullptr);
-    void setDefaults    (const rtengine::procparams::ProcParams* defParams, const ParamsEdited* pedited = nullptr);
-    void setBatchMode   (bool batchMode);
-    void curveChanged   (CurveEditor* ce);
-    void setEditProvider     (EditDataProvider *provider);
-    void autoOpenCurve  ();
-
-    void adjusterChanged (Adjuster* a, double newval);
-    void enabledChanged  ();
-    void enhanceChanged  ();
-    void medianChanged  ();
-    void autochromaChanged  ();
-    void chromaChanged (double autchroma, double autred, double autblue);
-    bool chromaComputed_ ();
-    void noiseChanged (double nresid, double highresid);
-    bool noiseComputed_ ();
-    void noiseTilePrev (int tileX, int tileY, int prevX, int prevY, int sizeT, int sizeP);
-    bool TilePrevComputed_ ();
-
-//    void perform_toggled  ();
-    void updateNoiseLabel      ();
-    void LmethodChanged      ();
-    void CmethodChanged      ();
-    void C2methodChanged      ();
-    void updateTileLabel      ();
-    void updatePrevLabel      ();
-
-    void dmethodChanged      ();
-    void medmethodChanged      ();
-    void methodmedChanged      ();
-    void rgbmethodChanged      ();
-    void smethodChanged      ();
-    virtual void colorForValue (double valX, double valY, enum ColorCaller::ElemType elemType, int callerId, ColorCaller* caller);
-
-    void setAdjusterBehavior (bool lumaadd, bool lumdetadd, bool chromaadd, bool chromaredadd, bool chromablueadd, bool gammaadd, bool passesadd);
-    void trimValues          (rtengine::procparams::ProcParams* pp);
-    Glib::ustring getSettingString ();
-
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/editorpanel.cc b/rtgui/editorpanel.cc
index 0783efe14c..8da176fc35 100644
--- a/rtgui/editorpanel.cc
+++ b/rtgui/editorpanel.cc
@@ -35,6 +35,44 @@
 
 using namespace rtengine::procparams;
 
+namespace
+{
+
+struct spparams {
+    double val;
+    Glib::ustring str;
+    MyProgressBar *pProgress;
+    Glib::RefPtr<Gtk::CssProvider> cssProvider;
+};
+
+int setprogressStrUI ( void *p )
+{
+    spparams *s = static_cast<spparams*> (p);
+
+    if ( ! s->str.empty() ) {
+        s->pProgress->set_text ( M (s->str) );
+    }
+
+    if ( s->val >= 0 ) {
+        s->pProgress->set_fraction ( s->val );
+
+        if (s->cssProvider) {
+            if ( s->val < 1.0 ) {
+                s->cssProvider->load_from_data ("ProgressBar { background-color: red }");
+            } else {
+                s->cssProvider->load_from_data ("ProgressBar { background-color: grey }");
+            }
+
+            s->pProgress->get_style_context()->set_background (s->pProgress->get_window());
+        }
+    }
+
+    delete s;
+    return FALSE;
+}
+
+}
+
 class EditorPanel::ColorManagementToolbar
 {
 private:
@@ -683,6 +721,7 @@ EditorPanel::EditorPanel (FilePanel* filePanel)
 
 EditorPanel::~EditorPanel ()
 {
+    idle_register.destroy();
 
     history->setHistoryBeforeLineListener (nullptr);
     // the order is important!
@@ -1017,46 +1056,12 @@ void EditorPanel::setProgressState (bool inProcessing)
     g_idle_add (setProgressStateUIThread, p);
 }
 
-struct spparams {
-    double val;
-    Glib::ustring str;
-    MyProgressBar *pProgress;
-    Glib::RefPtr<Gtk::CssProvider> cssProvider;
-
-};
-
-int setprogressStrUI ( void *p )
-{
-    spparams *s = static_cast<spparams*> (p);
-
-    if ( ! s->str.empty() ) {
-        s->pProgress->set_text ( M (s->str) );
-    }
-
-    if ( s->val >= 0 ) {
-        s->pProgress->set_fraction ( s->val );
-
-        if (s->cssProvider) {
-            if ( s->val < 1.0 ) {
-                s->cssProvider->load_from_data ("ProgressBar { background-color: red }");
-            } else {
-                s->cssProvider->load_from_data ("ProgressBar { background-color: grey }");
-            }
-
-            s->pProgress->get_style_context()->set_background (s->pProgress->get_window());
-        }
-    }
-
-    delete s;
-    return 0;
-}
-
 void EditorPanel::setProgress (double p)
 {
     spparams *s = new spparams;
     s->val = p;
     s->pProgress = progressLabel;
-    add_idle (setprogressStrUI, s);
+    idle_register.add(setprogressStrUI, s);
 }
 
 void EditorPanel::setProgressStr (Glib::ustring str)
@@ -1065,7 +1070,7 @@ void EditorPanel::setProgressStr (Glib::ustring str)
     s->str = str;
     s->val = -1;
     s->pProgress = progressLabel;
-    add_idle (setprogressStrUI, s);
+    idle_register.add(setprogressStrUI, s);
 }
 
 // This is only called from the ThreadUI, so within the gtk thread
diff --git a/rtgui/editorpanel.h b/rtgui/editorpanel.h
index d87f12c231..609df52369 100644
--- a/rtgui/editorpanel.h
+++ b/rtgui/editorpanel.h
@@ -45,19 +45,104 @@ struct EditorPanelIdleHelper {
 };
 
 class RTWindow;
-class EditorPanel : public Gtk::VBox,
+class EditorPanel final :
+    public Gtk::VBox,
     public PParamsChangeListener,
     public rtengine::ProgressListener,
     public ThumbnailListener,
     public HistoryBeforeLineListener,
     public rtengine::HistogramListener
 {
+public:
+    explicit EditorPanel (FilePanel* filePanel = nullptr);
+    ~EditorPanel ();
+
+    void open (Thumbnail* tmb, rtengine::InitialImage* isrc);
+    void setAspect ();
+    void on_realize ();
+    void leftPaneButtonReleased (GdkEventButton *event);
+    void rightPaneButtonReleased (GdkEventButton *event);
+
+    void setParent (RTWindow* p)
+    {
+        parent = p;
+    }
+    void writeOptions();
+
+    void showTopPanel (bool show);
+    bool isRealized()
+    {
+        return realized;
+    }
+    // progresslistener interface
+    void setProgress (double p);
+    void setProgressStr (Glib::ustring str);
+    void setProgressState (bool inProcessing);
+    void error (Glib::ustring title, Glib::ustring descr);
+    void displayError (Glib::ustring title, Glib::ustring descr);  // this is called by error in the gtk thread
+    void refreshProcessingState (bool inProcessing); // this is called by setProcessingState in the gtk thread
+
+    // PParamsChangeListener interface
+    void procParamsChanged (rtengine::procparams::ProcParams* params, rtengine::ProcEvent ev, Glib::ustring descr, ParamsEdited* paramsEdited = nullptr);
+
+    // thumbnaillistener interface
+    void procParamsChanged (Thumbnail* thm, int whoChangedIt);
+
+    // HistoryBeforeLineListener
+    void historyBeforeLineChanged (const rtengine::procparams::ProcParams& params);
+
+    // HistogramListener
+    void histogramChanged (LUTu & histRed, LUTu & histGreen, LUTu & histBlue, LUTu & histLuma, LUTu & histToneCurve, LUTu & histLCurve, LUTu & histCCurve,/* LUTu & histCLurve, LUTu & histLLCurve,*/ LUTu & histLCAM, LUTu & histCCAM,
+                           LUTu & histRedRaw, LUTu & histGreenRaw, LUTu & histBlueRaw, LUTu & histChroma, LUTu & histLRETI);
+
+    // event handlers
+    void info_toggled ();
+    void hideHistoryActivated ();
+    void tbRightPanel_1_toggled ();
+    void tbTopPanel_1_toggled ();
+    void beforeAfterToggled ();
+    void tbBeforeLock_toggled();
+    void saveAsPressed ();
+    void queueImgPressed ();
+    void sendToGimpPressed ();
+    void openNextEditorImage ();
+    void openPreviousEditorImage ();
+    void syncFileBrowser ();
+
+    void tbTopPanel_1_visible (bool visible);
+    bool CheckSidePanelsVisibility();
+    void tbShowHideSidePanels_managestate();
+    void toggleSidePanels();
+    void toggleSidePanelsZoomFit();
+
+    void saveProfile ();
+    Glib::ustring getShortName ();
+    Glib::ustring getFileName ();
+    bool handleShortcutKey (GdkEventKey* event);
+
+    bool getIsProcessing() const
+    {
+        return isProcessing;
+    }
+    void updateProfiles(const Glib::ustring &printerProfile, rtengine::RenderingIntent printerIntent, bool printerBPC);
+    void updateTPVScrollbar (bool hide);
+    void updateTabsUsesIcons (bool useIcons);
+    void updateHistogramPosition (int oldPosition, int newPosition);
+
+    Gtk::Paned* catalogPane;
+
 private:
+    void close ();
+
+    BatchQueueEntry*    createBatchQueueEntry ();
+    bool                idle_imageSaved (ProgressConnector<int> *pc, rtengine::IImage16* img, Glib::ustring fname, SaveFormat sf);
+    bool                idle_saveImage (ProgressConnector<rtengine::IImage16*> *pc, Glib::ustring fname, SaveFormat sf);
+    bool                idle_sendToGimp ( ProgressConnector<rtengine::IImage16*> *pc, Glib::ustring fname);
+    bool                idle_sentToGimp (ProgressConnector<int> *pc, rtengine::IImage16* img, Glib::ustring filename);
 
     Glib::ustring lastSaveAsFileName;
     bool realized;
 
-protected:
     MyProgressBar  *progressLabel;
     Gtk::ToggleButton* info;
     Gtk::ToggleButton* hidehp;
@@ -122,13 +207,6 @@ class EditorPanel : public Gtk::VBox,
 
     EditorPanelIdleHelper* epih;
 
-    void close ();
-
-    BatchQueueEntry*    createBatchQueueEntry ();
-    bool                idle_imageSaved (ProgressConnector<int> *pc, rtengine::IImage16* img, Glib::ustring fname, SaveFormat sf);
-    bool                idle_saveImage (ProgressConnector<rtengine::IImage16*> *pc, Glib::ustring fname, SaveFormat sf);
-    bool                idle_sendToGimp ( ProgressConnector<rtengine::IImage16*> *pc, Glib::ustring fname);
-    bool                idle_sentToGimp (ProgressConnector<int> *pc, rtengine::IImage16* img, Glib::ustring filename);
     int err;
 
     time_t processingStartedTime;
@@ -137,84 +215,7 @@ class EditorPanel : public Gtk::VBox,
 
     bool isProcessing;
 
-
-public:
-    explicit EditorPanel (FilePanel* filePanel = nullptr);
-    virtual ~EditorPanel ();
-
-    void open (Thumbnail* tmb, rtengine::InitialImage* isrc);
-    void setAspect ();
-    void on_realize ();
-    void leftPaneButtonReleased (GdkEventButton *event);
-    void rightPaneButtonReleased (GdkEventButton *event);
-
-    void setParent (RTWindow* p)
-    {
-        parent = p;
-    }
-    void writeOptions();
-
-    void showTopPanel (bool show);
-    bool isRealized()
-    {
-        return realized;
-    }
-    // progresslistener interface
-    void setProgress (double p);
-    void setProgressStr (Glib::ustring str);
-    void setProgressState (bool inProcessing);
-    void error (Glib::ustring title, Glib::ustring descr);
-    void displayError (Glib::ustring title, Glib::ustring descr);  // this is called by error in the gtk thread
-    void refreshProcessingState (bool inProcessing); // this is called by setProcessingState in the gtk thread
-
-    // PParamsChangeListener interface
-    void procParamsChanged (rtengine::procparams::ProcParams* params, rtengine::ProcEvent ev, Glib::ustring descr, ParamsEdited* paramsEdited = nullptr);
-
-    // thumbnaillistener interface
-    void procParamsChanged (Thumbnail* thm, int whoChangedIt);
-
-    // HistoryBeforeLineListener
-    void historyBeforeLineChanged (const rtengine::procparams::ProcParams& params);
-
-    // HistogramListener
-    void histogramChanged (LUTu & histRed, LUTu & histGreen, LUTu & histBlue, LUTu & histLuma, LUTu & histToneCurve, LUTu & histLCurve, LUTu & histCCurve,/* LUTu & histCLurve, LUTu & histLLCurve,*/ LUTu & histLCAM, LUTu & histCCAM,
-                           LUTu & histRedRaw, LUTu & histGreenRaw, LUTu & histBlueRaw, LUTu & histChroma, LUTu & histLRETI);
-
-    // event handlers
-    void info_toggled ();
-    void hideHistoryActivated ();
-    void tbRightPanel_1_toggled ();
-    void tbTopPanel_1_toggled ();
-    void beforeAfterToggled ();
-    void tbBeforeLock_toggled();
-    void saveAsPressed ();
-    void queueImgPressed ();
-    void sendToGimpPressed ();
-    void openNextEditorImage ();
-    void openPreviousEditorImage ();
-    void syncFileBrowser ();
-
-    void tbTopPanel_1_visible (bool visible);
-    bool CheckSidePanelsVisibility();
-    void tbShowHideSidePanels_managestate();
-    void toggleSidePanels();
-    void toggleSidePanelsZoomFit();
-
-    void saveProfile ();
-    Glib::ustring getShortName ();
-    Glib::ustring getFileName ();
-    bool handleShortcutKey (GdkEventKey* event);
-
-    bool getIsProcessing() const
-    {
-        return isProcessing;
-    }
-    void updateProfiles(const Glib::ustring &printerProfile, rtengine::RenderingIntent printerIntent, bool printerBPC);
-    void updateTPVScrollbar (bool hide);
-    void updateTabsUsesIcons (bool useIcons);
-    void updateHistogramPosition (int oldPosition, int newPosition);
-
-    Gtk::Paned *catalogPane;
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/filepanel.cc b/rtgui/filepanel.cc
index 8c7bae0fa5..ed9b70e8dc 100644
--- a/rtgui/filepanel.cc
+++ b/rtgui/filepanel.cc
@@ -22,12 +22,6 @@
 #include "inspector.h"
 #include "placesbrowser.h"
 
-int FilePanelInitUI (void* data)
-{
-    (static_cast<FilePanel*>(data))->init ();
-    return 0;
-}
-
 FilePanel::FilePanel () : parent(nullptr)
 {
 
@@ -143,13 +137,21 @@ FilePanel::FilePanel () : parent(nullptr)
     fileCatalog->setFileSelectionChangeListener (tpc);
 
     fileCatalog->setFileSelectionListener (this);
-    add_idle (FilePanelInitUI, this);
+
+    const auto func = [](gpointer data) -> gboolean {
+        static_cast<FilePanel*>(data)->init();
+        return FALSE;
+    };
+
+    idle_register.add(func, this);
 
     show_all ();
 }
 
 FilePanel::~FilePanel ()
 {
+    idle_register.destroy();
+
     rightNotebookSwitchConn.disconnect();
 
     if (inspectorPanel) {
diff --git a/rtgui/filepanel.h b/rtgui/filepanel.h
index 68f021043b..d54f5f75a5 100644
--- a/rtgui/filepanel.h
+++ b/rtgui/filepanel.h
@@ -33,38 +33,12 @@
 #include "progressconnector.h"
 
 class RTWindow;
-class FilePanel : public Gtk::HPaned,
+
+class FilePanel final :
+    public Gtk::HPaned,
     public FileSelectionListener,
     public PParamsChangeListener
 {
-
-protected:
-    //DirBrowser* dirBrowser;
-    PlacesBrowser* placesBrowser;
-    RecentBrowser* recentBrowser;
-    // FileCatalog* fileCatalog;   // filecatalog is the file browser with the button bar above it
-
-    Inspector* inspectorPanel;
-    Gtk::VPaned* tpcPaned;
-    BatchToolPanelCoordinator* tpc;
-    History* history;
-    //FilterPanel* filterPanel;
-    RTWindow* parent;
-    Gtk::Notebook* rightNotebook;
-    sigc::connection rightNotebookSwitchConn;
-
-    struct pendingLoad {
-        bool complete;
-        ProgressConnector<rtengine::InitialImage*> *pc;
-        Thumbnail *thm;
-    };
-    MyMutex pendingLoadMutex;
-    std::vector<struct pendingLoad*> pendingLoads;
-
-    int error;
-
-    void on_NB_switch_page(Gtk::Widget* page, guint page_num);
-
 public:
     FilePanel ();
     ~FilePanel ();
@@ -107,6 +81,32 @@ class FilePanel : public Gtk::HPaned,
     bool handleShortcutKey (GdkEventKey* event);
     void updateTPVScrollbar (bool hide);
     void updateTabsUsesIcons (bool useIcons);
+
+private:
+    void on_NB_switch_page(Gtk::Widget* page, guint page_num);
+
+    PlacesBrowser* placesBrowser;
+    RecentBrowser* recentBrowser;
+
+    Inspector* inspectorPanel;
+    Gtk::VPaned* tpcPaned;
+    BatchToolPanelCoordinator* tpc;
+    History* history;
+    RTWindow* parent;
+    Gtk::Notebook* rightNotebook;
+    sigc::connection rightNotebookSwitchConn;
+
+    struct pendingLoad {
+        bool complete;
+        ProgressConnector<rtengine::InitialImage*> *pc;
+        Thumbnail *thm;
+    };
+    MyMutex pendingLoadMutex;
+    std::vector<struct pendingLoad*> pendingLoads;
+
+    int error;
+
+    IdleRegister idle_register;
 };
 
 #endif
diff --git a/rtgui/guiutils.cc b/rtgui/guiutils.cc
index 43bfc11b0c..e8310ff0ef 100644
--- a/rtgui/guiutils.cc
+++ b/rtgui/guiutils.cc
@@ -43,6 +43,53 @@ guint add_idle (GSourceFunc function, gpointer data)
     //gtk_main_iteration_do(false);
 }
 
+IdleRegister::~IdleRegister()
+{
+    destroy();
+}
+
+void IdleRegister::add(GSourceFunc function, gpointer data)
+{
+    struct DataWrapper {
+        IdleRegister* const self;
+        GSourceFunc function;
+        gpointer data;
+    };
+
+    const auto dispatch = [](gpointer data) -> gboolean {
+        DataWrapper* const data_wrapper = static_cast<DataWrapper*>(data);
+
+        if (!data_wrapper->function(data_wrapper->data)) {
+            data_wrapper->self->mutex.lock();
+            data_wrapper->self->ids.erase(data_wrapper);
+            data_wrapper->self->mutex.unlock();
+
+            delete data_wrapper;
+            return FALSE;
+        }
+
+        return TRUE;
+    };
+
+    DataWrapper* const data_wrapper = new DataWrapper{
+        this,
+        function,
+        data
+    };
+
+    mutex.lock();
+    ids[data_wrapper] = add_idle(dispatch, data_wrapper);
+    mutex.unlock();
+}
+
+void IdleRegister::destroy()
+{
+    mutex.lock();
+    for (const auto id : ids) {
+        g_source_remove(id.second);
+    }
+    mutex.unlock();
+}
 
 /*
 gboolean giveMeAGo(void* data) {
diff --git a/rtgui/guiutils.h b/rtgui/guiutils.h
index e5919c9e45..12370a571d 100644
--- a/rtgui/guiutils.h
+++ b/rtgui/guiutils.h
@@ -19,13 +19,17 @@
 #ifndef __GUI_UTILS_
 #define __GUI_UTILS_
 
+#include <map>
+
 #include <gtkmm.h>
+
 #include <cairomm/cairomm.h>
-#include "../rtengine/rtengine.h"
+
 #include "../rtengine/coord.h"
+#include "../rtengine/noncopyable.h"
+#include "../rtengine/rtengine.h"
+
 #include "rtimage.h"
-#include <sstream>
-#include <iostream>
 
 Glib::ustring escapeHtmlChars(const Glib::ustring &src);
 bool removeIfThere (Gtk::Container* cont, Gtk::Widget* w, bool increference = true);
@@ -40,6 +44,20 @@ void setExpandAlignProperties(Gtk::Widget *widget, bool hExpand, bool vExpand, e
 
 guint add_idle (GSourceFunc function, gpointer data);
 
+class IdleRegister final :
+    public rtengine::NonCopyable
+{
+public:
+    ~IdleRegister();
+
+    void add(GSourceFunc function, gpointer data);
+    void destroy();
+
+private:
+    std::map<void*, guint> ids;
+    MyMutex mutex;
+};
+
 // TODO: The documentation says gdk_threads_enter and gdk_threads_leave should be replaced
 // by g_main_context_invoke(), g_idle_add() and related functions, but this will require more extensive changes.
 // We silence those warnings until then so that we notice the others.
diff --git a/rtgui/resize.cc b/rtgui/resize.cc
index 0504a39340..bf2d4ce675 100644
--- a/rtgui/resize.cc
+++ b/rtgui/resize.cc
@@ -118,7 +118,7 @@ Resize::Resize () : FoldableToolPanel(this, "resize", M("TP_RESIZE_LABEL"), fals
 
 Resize::~Resize ()
 {
-
+    idle_register.destroy();
     delete scale;
     delete sizeBox;
 }
@@ -352,68 +352,76 @@ void Resize::sizeChanged (int mw, int mh, int ow, int oh)
 
 void Resize::setDimensions ()
 {
+    const auto func = [](gpointer data) -> gboolean {
+        Resize* const self = static_cast<Resize*>(data);
 
-    int refw, refh;
+        self->wconn.block(true);
+        self->hconn.block(true);
+        self->scale->block(true);
 
-    wconn.block (true);
-    hconn.block (true);
-    scale->block(true);
+        int refw, refh;
 
-    if (appliesTo->get_active_row_number() == 0 && cropw) {
-        // Applies to Cropped area
-        refw = cropw;
-        refh = croph;
-    } else {
-        // Applies to Full image or crop is disabled
-        refw = maxw;
-        refh = maxh;
-    }
+        if (self->appliesTo->get_active_row_number() == 0 && self->cropw) {
+            // Applies to Cropped area
+            refw = self->cropw;
+            refh = self->croph;
+        } else {
+            // Applies to Full image or crop is disabled
+            refw = self->maxw;
+            refh = self->maxh;
+        }
 
-    GThreadLock lock;
-    w->set_range (32, 4 * refw);
-    h->set_range (32, 4 * refh);
+        self->w->set_range(32, 4 * refw);
+        self->h->set_range(32, 4 * refh);
 
-    double tmpScale;
+        switch (self->spec->get_active_row_number()) {
+            case 0: {
+                // Scale mode
+                self->w->set_value(static_cast<double>(static_cast<int>(static_cast<double>(refw) * self->scale->getValue() + 0.5)));
+                self->h->set_value(static_cast<double>(static_cast<int>(static_cast<double>(refh) * self->scale->getValue() + 0.5)));
+                break;
+            }
 
-    switch (spec->get_active_row_number()) {
-    case (0):   // Scale mode
-        w->set_value((double)((int)( (double)(refw) * scale->getValue() + 0.5) ));
-        h->set_value((double)((int)( (double)(refh) * scale->getValue() + 0.5) ));
-        break;
+            case 1: {
+                // Width mode
+                const double tmp_scale = self->w->get_value() / static_cast<double>(refw);
+                self->scale->setValue(tmp_scale);
+                self->h->set_value(static_cast<double>(static_cast<int>(static_cast<double>(refh) * tmp_scale + 0.5)));
+                break;
+            }
 
-    case (1):   // Width mode
-        tmpScale = w->get_value() / (double)refw;
-        scale->setValue (tmpScale);
-        h->set_value((double)((int)( (double)(refh) * tmpScale + 0.5) ));
-        break;
+            case 2: {
+                // Height mode
+                const double tmp_scale = self->h->get_value() / static_cast<double>(refh);
+                self->scale->setValue(tmp_scale);
+                self->w->set_value(static_cast<double>(static_cast<int>(static_cast<double>(refw) * tmp_scale + 0.5)));
+                break;
+            }
 
-    case (2):   // Height mode
-        tmpScale = h->get_value() / (double)refh;
-        scale->setValue (tmpScale);
-        w->set_value((double)((int)( (double)(refw) * tmpScale + 0.5) ));
-        break;
+            case 3: {
+                // Bounding box mode
+                const double tmp_scale =
+                    self->w->get_value() / self->h->get_value() < static_cast<double>(refw) / static_cast<double>(refh)
+                        ? self->w->get_value() / static_cast<double>(refw)
+                        : self->h->get_value() / static_cast<double>(refh);
 
-    case (3): { // Bounding box mode
-        double wSliderValue = w->get_value();
-        double hSliderValue = h->get_value();
+                self->scale->setValue(tmp_scale);
+                break;
+            }
 
-        if ( (wSliderValue / hSliderValue) < ((double)refw / (double)refh)) {
-            tmpScale = wSliderValue / (double)refw;
-        } else {
-            tmpScale = hSliderValue / (double)refh;
+            default: {
+                break;
+            }
         }
 
-        scale->setValue (tmpScale);
-        break;
-    }
+        self->scale->block(false);
+        self->wconn.block(false);
+        self->hconn.block(false);
 
-    default:
-        break;
-    }
+        return FALSE;
+    };
 
-    scale->block(false);
-    wconn.block (false);
-    hconn.block (false);
+    idle_register.add(func, this);
 }
 
 void Resize::fitBoxScale()
diff --git a/rtgui/resize.h b/rtgui/resize.h
index cf640c281d..acba5b4783 100644
--- a/rtgui/resize.h
+++ b/rtgui/resize.h
@@ -25,25 +25,13 @@
 #include "toolpanel.h"
 #include "guiutils.h"
 
-class Resize : public ToolParamBlock, public AdjusterListener, public FoldableToolPanel, public rtengine::SizeListener
+class Resize final :
+    public ToolParamBlock,
+    public AdjusterListener,
+    public FoldableToolPanel,
+    public rtengine::SizeListener
 {
-
-protected:
-    Adjuster*          scale;
-    Gtk::VBox*         sizeBox;
-    MyComboBoxText*    appliesTo;
-    MyComboBoxText*    method;
-    MyComboBoxText*    spec;
-    MySpinButton*      w;
-    MySpinButton*      h;
-    int                maxw, maxh;
-    int                cropw, croph;
-    sigc::connection   sconn, aconn, wconn, hconn;
-    bool               wDirty, hDirty;
-    ToolParamBlock*    packBox;
-
 public:
-
     Resize ();
     ~Resize ();
 
@@ -75,6 +63,20 @@ class Resize : public ToolParamBlock, public AdjusterListener, public FoldableTo
     int getComputedHeight ();
     void notifyBBox ();
     void updateGUI ();
+
+    Adjuster*          scale;
+    Gtk::VBox*         sizeBox;
+    MyComboBoxText*    appliesTo;
+    MyComboBoxText*    method;
+    MyComboBoxText*    spec;
+    MySpinButton*      w;
+    MySpinButton*      h;
+    int                maxw, maxh;
+    int                cropw, croph;
+    sigc::connection   sconn, aconn, wconn, hconn;
+    bool               wDirty, hDirty;
+    ToolParamBlock*    packBox;
+    IdleRegister       idle_register;
 };
 
 #endif