Fix crash with PythonAlgorithm registration on windows. Refs #6122

There were several issues. First, there were two signal updates happening
at the same time: one from MantidUI and another from
AlgorithmSelectorWidget. Secondly, the AlgorithmSelectorWidget was
receiving a Poco::Notification from a separate thread and not dispatching
it to the GUI thread but instead calling update directly.

Code/Mantid/Framework/PythonAPI/PythonAlgorithms/MaskWorkspaceToCalFile.py

@@ -4,10 +4,9 @@
 
 *WIKI*"""
 import sys
-from MantidFramework import *
-from mantid.simpleapi import *
+from mantid.kernel import *
 from mantid.api import *
-#from mantid.kernel import *
+from mantid.simpleapi import *
 
 class QueryFlag:
         def isMasked(self, detector, yValue):

Code/Mantid/Framework/PythonAPI/src/FrameworkManagerProxy.cpp

@@ -21,6 +21,7 @@
 #include <vector>
 #include "MantidAPI/IMDHistoWorkspace.h"
 #include "MantidAPI/IPeaksWorkspace.h"
+#include <Poco/ScopedLock.h>
 
 using Mantid::API::AlgorithmManager;
 using Mantid::API::IPeaksWorkspace;
@@ -534,6 +535,11 @@ bool FrameworkManagerProxy::workspaceExists(const std::string & name) const
   return API::AnalysisDataService::Instance().doesExist(name);
 }
 
+namespace
+{
+  Poco::Mutex PYALG_REGISTER_MUTEX;
+}
+
 /**
  * Add a python algorithm to the algorithm factory
  * @param pyobj :: The python algorithm object wrapped in a boost object
@@ -547,6 +553,9 @@ void FrameworkManagerProxy::registerPyAlgorithm(boost::python::object pyobj)
   using boost::python::handle;
   using boost::python::borrowed;
 
+  // Serialize write access to the factory
+  Poco::ScopedLock<Poco::Mutex> lock(PYALG_REGISTER_MUTEX);
+
   PyObject *classObject = PyObject_GetAttrString(pyobj.ptr(), "__class__");
   object classType(handle<>(borrowed(classObject)));
   // Takes ownership of instantiator and replaces any existing algorithm

Code/Mantid/Framework/PythonInterface/mantid/api/src/Exports/AlgorithmFactory.cpp

@@ -5,6 +5,7 @@
 
 #include <boost/python/class.hpp>
 #include <boost/python/def.hpp>
+#include <Poco/ScopedLock.h>
 
 // Python frameobject. This is under the boost includes so that boost will have done the
 // include of Python.h which it ensures is done correctly
@@ -73,14 +74,24 @@ void export_AlgorithmFactory()
 
 namespace
 {
-  // A function to register an algorithm from Python
-  void registerAlgorithm(boost::python::object obj)
-  {
     using Mantid::PythonInterface::PythonObjectInstantiator;
     using Mantid::Kernel::AbstractInstantiator;
     using Mantid::PythonInterface::AlgorithmWrapper;
     using Mantid::API::Algorithm;
     using Mantid::API::IAlgorithm_sptr;
+
+  /// Python algorithm registration mutex in anonymous namespace (aka static)
+  Poco::Mutex PYALG_REGISTER_MUTEX;
+
+  /**
+   * A free function to register an algorithm from Python
+   * @param obj :: A Python object that should either be a class type derived from PythonAlgorithm
+   *              or an instance of a class type derived from PythonAlgorithm
+   */
+  void registerAlgorithm(boost::python::object obj)
+  {
+    Poco::ScopedLock<Poco::Mutex> lock(PYALG_REGISTER_MUTEX);
+
     static PyObject * const pyAlgClass = (PyObject*)converter::registered<AlgorithmWrapper>::converters.to_python_target_type();
     // obj could be or instance/class, check instance first
     PyObject *classObject(NULL);

Code/Mantid/MantidPlot/src/Mantid/MantidUI.cpp

@@ -79,7 +79,6 @@ m_finishedLoadDAEObserver(*this, &MantidUI::handleLoadDAEFinishedNotification),
   m_replaceObserver(*this,&MantidUI::handleReplaceWorkspace),
   m_deleteObserver(*this,&MantidUI::handleDeleteWorkspace),
   m_clearADSObserver(*this,&MantidUI::handleClearADS),
-  m_algUpdatesObserver(*this, &MantidUI::handleAlgorithmFactoryUpdates),
   m_renameObserver(*this,&MantidUI::handleRenameWorkspace),
   m_groupworkspacesObserver(*this,&MantidUI::handleGroupWorkspaces),
   m_ungroupworkspaceObserver(*this,&MantidUI::handleUnGroupWorkspace),
@@ -194,10 +193,6 @@ void MantidUI::init()
     showCritical("The curve fitting plugin is missing");
   }
 
-  //connect the signal from the algorithm factory to monitor updates
-  connect(this, SIGNAL(algorithms_updated()), m_exploreAlgorithms, SLOT(update()));
-  Mantid::API::AlgorithmFactory::Instance().notificationCenter.addObserver(m_algUpdatesObserver);
-
 }
 
 /// Slot: Receives a new X range from a FitPropertyBrowser and re-emits it.
@@ -293,7 +288,6 @@ MantidUI::~MantidUI()
   Mantid::API::AnalysisDataService::Instance().notificationCenter.removeObserver(m_replaceObserver);
   Mantid::API::AnalysisDataService::Instance().notificationCenter.removeObserver(m_deleteObserver);
   Mantid::API::AnalysisDataService::Instance().notificationCenter.removeObserver(m_clearADSObserver);
-  Mantid::API::AnalysisDataService::Instance().notificationCenter.removeObserver(m_algUpdatesObserver);
 }
 
 void MantidUI::saveSettings() const
@@ -1779,10 +1773,6 @@ void MantidUI::handleClearADS(Mantid::API::ClearADSNotification_ptr)
   emit workspaces_cleared();
 }
 
-void MantidUI::handleAlgorithmFactoryUpdates(Mantid::API::AlgorithmFactoryUpdateNotification_ptr)
-{
-  emit algorithms_updated();
-}
 void MantidUI::handleRenameWorkspace(Mantid::API::WorkspaceRenameNotification_ptr pNf)
 {
   emit workspace_renamed(QString::fromStdString(pNf->object_name()), QString::fromStdString(pNf->new_objectname()));

Code/Mantid/MantidPlot/src/Mantid/MantidUI.h

@@ -298,7 +298,6 @@ public slots:
   void workspace_replaced(const QString &, Mantid::API::Workspace_sptr);
   void workspace_removed(const QString &);
   void workspaces_cleared();
-  void algorithms_updated();
   void workspace_renamed(const QString &, const QString &);
   void workspaces_grouped(const QStringList&);
   void workspace_ungrouped(const QString&, Mantid::API::Workspace_sptr);
@@ -457,9 +456,6 @@ public slots:
   void handleClearADS(Mantid::API::ClearADSNotification_ptr pNf);
   Poco::NObserver<MantidUI, Mantid::API::ClearADSNotification> m_clearADSObserver;
 
-  void handleAlgorithmFactoryUpdates(Mantid::API::AlgorithmFactoryUpdateNotification_ptr pNf);
-  Poco::NObserver<MantidUI, Mantid::API::AlgorithmFactoryUpdateNotification> m_algUpdatesObserver;
-
   //handles rename workspace notification
   void handleRenameWorkspace(Mantid::API::WorkspaceRenameNotification_ptr pNf);
   Poco::NObserver<MantidUI, Mantid::API::WorkspaceRenameNotification> m_renameObserver;

Code/Mantid/MantidQt/MantidWidgets/inc/MantidQtMantidWidgets/AlgorithmSelectorWidget.h

@@ -47,7 +47,8 @@ namespace MantidWidgets
     void findAlgTextChanged(const QString& text);
     void treeSelectionChanged();
 
-  signals:
+signals:
+    void algorithmFactoryUpdateReceived();
     void executeAlgorithm(const QString &, int);
     void algorithmSelectionChanged(const QString &, int);
 

Code/Mantid/MantidQt/MantidWidgets/src/AlgorithmSelectorWidget.cpp

@@ -50,7 +50,11 @@ namespace MantidWidgets
     layout->addLayout(buttonLayout);
     layout->addWidget(m_tree);
 
+    // The poco notification will be dispacted from the callers thread but we need to
+    // make sure the updates to the widgets happen on the GUI thread. Dispatching
+    // through a Qt signal will make sure it is in the correct thread.
     AlgorithmFactory::Instance().notificationCenter.addObserver(m_updateObserver);
+    connect(this, SIGNAL(algorithmFactoryUpdateReceived()), this, SLOT(update()));
   }
 
   //----------------------------------------------------------------------------------------------
@@ -178,10 +182,7 @@ namespace MantidWidgets
   void AlgorithmSelectorWidget::
   handleAlgorithmFactoryUpdate(Mantid::API::AlgorithmFactoryUpdateNotification_ptr)
   {
-    if(!m_updateInProgress)
-    {
-      this->update();
-    }
+    emit algorithmFactoryUpdateReceived();
   }
 
   //============================================================================