Factor out "write-temp-file-then-replace" code into AtomicFileOverwri…

…ter class.

git-svn-id: https://scantailor.svn.sourceforge.net/svnroot/scantailor/trunk@133 80b70061-164d-0410-b7b7-e274ec932871

AtomicFileOverwriter.cpp

@@ -0,0 +1,81 @@
+/*
+    Scan Tailor - Interactive post-processing tool for scanned pages.
+    Copyright (C) 2007-2008  Joseph Artsimovich <joseph_a@mail.ru>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "AtomicFileOverwriter.h"
+#include "Utils.h"
+#include <QString>
+#include <QFile>
+#include <QTemporaryFile>
+
+AtomicFileOverwriter::AtomicFileOverwriter()
+{
+}
+
+AtomicFileOverwriter::~AtomicFileOverwriter()
+{
+	abort();
+}
+
+QIODevice*
+AtomicFileOverwriter::startWriting(QString const& file_path)
+{
+	abort();
+
+	m_ptrTempFile.reset(new QTemporaryFile(file_path));
+	m_ptrTempFile->setAutoRemove(false);
+	if (!m_ptrTempFile->open()) {
+		m_ptrTempFile->reset();
+	}
+
+	return m_ptrTempFile.get();
+}
+
+bool
+AtomicFileOverwriter::commit()
+{
+	if (!m_ptrTempFile.get()) {
+		return false;
+	}
+
+	QString const temp_file_path(m_ptrTempFile->fileName());
+	QString const target_path(m_ptrTempFile->fileTemplate());
+
+	// Yes, we have to destroy this object here, because:
+	// 1. Under Windows, open files can't be renamed or deleted.
+	// 2. QTemporaryFile::close() doesn't really close it.
+	m_ptrTempFile.reset();
+
+	if (!Utils::renameFile(temp_file_path, target_path)) {
+		QFile::remove(temp_file_path);
+		return false;
+	}
+
+	return true;
+}
+
+void
+AtomicFileOverwriter::abort()
+{
+	if (!m_ptrTempFile.get()) {
+		return;
+	}
+
+	QString const temp_file_path(m_ptrTempFile->fileName());
+	m_ptrTempFile.reset(); // See comments in commit()
+	QFile::remove(temp_file_path);
+}

AtomicFileOverwriter.h

@@ -0,0 +1,75 @@
+/*
+    Scan Tailor - Interactive post-processing tool for scanned pages.
+    Copyright (C) 2007-2008  Joseph Artsimovich <joseph_a@mail.ru>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef ATOMICFILEOVERWRITER_H_
+#define ATOMICFILEOVERWRITER_H_
+
+#include "NonCopyable.h"
+#include <memory>
+
+class QString;
+class QIODevice;
+class QTemporaryFile;
+
+/**
+ * \brief Overwrites files by writing to a temporary file and then replacing
+ *        the target file with it.
+ *
+ * Because renaming across volumes doesn't work, we create a temporary file
+ * in the same directory as the target file.
+ */
+class AtomicFileOverwriter
+{
+	DECLARE_NON_COPYABLE(AtomicFileOverwriter)
+public:
+	AtomicFileOverwriter();
+
+	/**
+	 * \brief Destroys the object and calls abort() if necessary.
+	 */
+	~AtomicFileOverwriter();
+
+	/**
+	 * \brief Start writing to a temporary file.
+	 *
+	 * \returns A temporary file as QIODevice, or null of temporary file
+	 *          could not be opened.  In latter case, calling abort()
+	 *          is not necessary.
+	 *
+	 * If a file is already being written, it calles abort() and then
+	 * proceeds as usual.
+	 */
+	QIODevice* startWriting(QString const& file_path);
+
+	/**
+	 * \brief Replaces the target file with the temporary one.
+	 *
+	 * If replacing failed, false is returned and the temporary file
+	 * is removed.
+	 */
+	bool commit();
+
+	/**
+	 * \brief Removes the temporary file without touching the target one.
+	 */
+	void abort();
+private:
+	std::auto_ptr<QTemporaryFile> m_ptrTempFile;
+};
+
+#endif

CMakeLists.txt

@@ -216,6 +216,7 @@ SET(
 	ProjectWriter.cpp ProjectWriter.h
 	XmlMarshaller.cpp XmlMarshaller.h
 	XmlUnmarshaller.cpp XmlUnmarshaller.h
+	AtomicFileOverwriter.cpp AtomicFileOverwriter.h
 	Utils.cpp Utils.h
 	AutoManualMode.h
 	AbstractCommand.h

ThumbnailPixmapCache.cpp

@@ -19,7 +19,7 @@
 #include "ThumbnailPixmapCache.h"
 #include "ImageId.h"
 #include "ImageLoader.h"
-#include "Utils.h"
+#include "AtomicFileOverwriter.h"
 #include "imageproc/Scale.h"
 #include <QCoreApplication>
 #include <QCryptographicHash>
@@ -29,8 +29,6 @@
 #include <QFileInfo>
 #include <QDir>
 #include <QFile>
-#include <QTemporaryFile>
-#include <QAbstractFileEngine>
 #include <QString>
 #include <QChar>
 #include <QImage>
@@ -453,16 +451,10 @@ ThumbnailPixmapCache::Impl::ensureThumbnailExists(
 
 	QImage const thumbnail(makeThumbnail(image, max_thumb_size));
 
-	// To avoid concurrently writing to the same file, we write
-	// to a temporary file and then replace the original.
-	QTemporaryFile temp_file(thumb_file_path);
-	temp_file.setAutoRemove(true);
-	if (temp_file.open()) {
-		if (thumbnail.save(&temp_file, "PNG")) {
-			if (Utils::renameFile(temp_file.fileName(), thumb_file_path)) {
-				temp_file.setAutoRemove(false);
-			}
-		}
+	AtomicFileOverwriter overwriter;
+	QIODevice* iodev = overwriter.startWriting(thumb_file_path);
+	if (thumbnail.save(iodev, "PNG")) {
+		overwriter.commit();
 	}
 }
 
@@ -487,17 +479,13 @@ ThumbnailPixmapCache::Impl::recreateThumbnail(
 	QImage const thumbnail(makeThumbnail(image, max_thumb_size));
 	bool thumb_written = false;
 
-	// To avoid concurrently writing to the same file, we write
-	// to a temporary file and then replace the original.
-	QTemporaryFile temp_file(thumb_file_path);
-	temp_file.setAutoRemove(true);
-	if (temp_file.open()) {
-		if (thumbnail.save(&temp_file, "PNG")) {
-			if (Utils::renameFile(temp_file.fileName(), thumb_file_path)) {
-				thumb_written = true;
-				temp_file.setAutoRemove(false);
-			}
-		}
+	// Note that we may be called from multiple threads at the same time.
+	AtomicFileOverwriter overwriter;
+	QIODevice* iodev = overwriter.startWriting(thumb_file_path);
+	if (thumbnail.save(iodev, "PNG")) {
+		thumb_written = overwriter.commit();
+	} else {
+		overwriter.abort();
 	}
 
 	if (!thumb_written) {