How to add multithread support to your Qt application - Revision history

Hamishwillee: Text replace - "`" to ""`


2012-10-11T01:17:04Z
Text replace - "<code cpp>" to "<code cpp-qt>"

			
			
			
			
		
		← Older revision
		Revision as of 01:17, 11 October 2012
		
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  The first step is to implement the {{Icode|QRunnable}} interface:   The first step is to implement the {{Icode|QRunnable}} interface:
− <code cpp> + <code cpp-qt>
  class LoadingThread : public QRunnable   class LoadingThread : public QRunnable
  {   {
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  The QML Camera component provides the {{Icode|onImageSaved ( path )}} signal, called after the image has been written to the filesystem, in this context connected to {{Icode|setShot}} slots. Here we create the {{Icode|LoadingThread}} to start memory loading process in the background.   The QML Camera component provides the {{Icode|onImageSaved ( path )}} signal, called after the image has been written to the filesystem, in this context connected to {{Icode|setShot}} slots. Here we create the {{Icode|LoadingThread}} to start memory loading process in the background.
    
− <code cpp> + <code cpp-qt>
  void QHdrCamera::setShot1(QString path) {   void QHdrCamera::setShot1(QString path) {
       if( !QFile::rename(path, QDir::toNativeSeparators(s_shot1)) ) {        if( !QFile::rename(path, QDir::toNativeSeparators(s_shot1)) ) {
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  The application has to wait until all threads finish their jobs. {{Icode|QThreadPool}} provides a method called {{Icode|waitForDone()}} that does that.   The application has to wait until all threads finish their jobs. {{Icode|QThreadPool}} provides a method called {{Icode|waitForDone()}} that does that.
    
− <code cpp> + <code cpp-qt>
  QThreadPool::globalInstance()->waitForDone();   QThreadPool::globalInstance()->waitForDone();
  </code>   </code>



Hamishwillee: Hamishwillee - Fix categories
2012-07-13T05:34:48Z
Hamishwillee - Fix categories

			
			
			
			
		
		← Older revision
		Revision as of 05:34, 13 July 2012
		
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− [[Category:Qt]][[Category:Symbian]][[Category:MeeGo Harmattan]][[Category:Code Examples]][[Category:Essential Idioms]][[Category:Thread]][[Category:Symbian^3]][[Category:Nokia Belle]] + [[Category:Qt]][[Category:Symbian]][[Category:MeeGo Harmattan]][[Category:Code Examples]][[Category:Symbian^3]][[Category:Nokia Belle]][[Category:Threading]]
  {{Abstract|This article explains how to use multi-threading on Qt, using the context of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] for the explanation.}}   {{Abstract|This article explains how to use multi-threading on Qt, using the context of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] for the explanation.}}
  {{SeeAlso|   {{SeeAlso|



Hamishwillee: Text replace - "Category:MeeGo" to "Category:MeeGo Harmattan"
2012-06-13T10:53:35Z
Text replace - "Category:MeeGo" to "Category:MeeGo Harmattan"

			
			
			
			
		
		← Older revision
		Revision as of 10:53, 13 June 2012
		
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− [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]][[Category:Essential Idioms]][[Category:Thread]][[Category:Symbian^3]][[Category:Nokia Belle]] + [[Category:Qt]][[Category:Symbian]][[Category:MeeGo Harmattan]][[Category:Code Examples]][[Category:Essential Idioms]][[Category:Thread]][[Category:Symbian^3]][[Category:Nokia Belle]]
  {{Abstract|This article explains how to use multi-threading on Qt, using the context of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] for the explanation.}}   {{Abstract|This article explains how to use multi-threading on Qt, using the context of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] for the explanation.}}
  {{SeeAlso|   {{SeeAlso|



Hamishwillee: Hamishwillee - Subedit. Fix categories. Restructure. Add cross links to other useful articles
2012-05-31T01:30:31Z
Hamishwillee - Subedit. Fix categories. Restructure. Add cross links to other useful articles

			
			
			
			
		
		← Older revision
		Revision as of 01:30, 31 May 2012
		
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− [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]] + [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]][[Category:Essential Idioms]][[Category:Thread]][[Category:Symbian^3]][[Category:Nokia Belle]]
− {{Note|This is an entry in the [[PureView Imaging Competition 2012Q2]]}} + {{Abstract|This article explains how to use multi-threading on Qt, using the context of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] for the explanation.}}
−   + {{SeeAlso|
  + * [[Multi-Threaded Image Processing using Qt Camera]]
  + * [http://qt-project.org/doc/qt-4.8/thread-basics.html Threading basic] (Qt reference)
  + * [http://qt-project.org/doc/qt-4.8/threads.html Thread support in Qt] (Qt reference)}}
  {{ArticleMetaData <!-- v1.2 -->   {{ArticleMetaData <!-- v1.2 -->
  |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->   |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->
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  |signing=<!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->   |signing=<!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->
  |capabilities= <!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->   |capabilities= <!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
− |keywords= Thread, QThread, QRunnable,QThreadPool + |keywords= Thread, QThread, QRunnable, QThreadPool
  |language= <!-- Language category code for non-English topics - e.g. Lang-Chinese -->   |language= <!-- Language category code for non-English topics - e.g. Lang-Chinese -->
  |translated-by= <!-- [[User:XXXX]] -->   |translated-by= <!-- [[User:XXXX]] -->
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  == Introduction ==   == Introduction ==
− This article explains how to manage multithreading in a mobile application.  [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] will be used as a showcase. + {{Note|This is an entry in the [[PureView Imaging Competition 2012Q2]]}}
    
− == Showcase  == + [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] is a QML component for creating [http://en.wikipedia.org/wiki/High_dynamic_range_imaging  High Dynamic Range images]. The component captures three photos at different exposure ranges and combines the best-exposed regions in each using appropriate algorithms (see [[QHdrCamera component for High Dynamic Range Imaging]] for more information).
− [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] is a component component able to create [http://en.wikipedia.org/wiki/High_dynamic_range_imaging  High Dynamic Range images]. + 
    
− Basically to do that the component captures three photos at different exposure range mixing them using some algorithms. For further information, please refer to [http://www.developer.nokia.com/Community/Wiki/QHdrCamera_component_for_High_Dynamic_Range_Imaging this article]. + The original single-threaded implementation first captured and saved all the images and then loaded them and started calculation of the HDR image. This was very slow, primarily because of the time taken to save and load images on some hardware.  
    
− Capturing images in sequence has to be done as fast as possible. Each time the QML component will be asked to shoot a frame it saves the captured image in the default path, after which it is ready to capture another frame. + Part of the solution to this problem has been to use multi-threading: as soon as the first image is saved we now start loading and processing it. As much of the loading and processing is now concurrent with image capture, the total execution time is much reduced.
−   + 
− After the process of capturing three images, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image. + 
−   + 
− The loading process is very slow, especially as resolution grows, due to the (at time of writing, May 2012) phone memory speed, so this impacts the overall processing time. If, during shooting the next frame, the application was also able to begin loading the previously saved frame into memory this will reduce the waiting time, enhancing user experience. + 
    
  The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRunnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html QThreadPool] class.   The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRunnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html QThreadPool] class.
    
− == QRunnable == + == Multithread Image Loading ==
− The {{Icode|QRunnable}} class is an interface for representing a task or piece of code that needs to be executed, represented by your reimplementation of the {{Icode|run()}} function. + {{Icode|QRunnable}} is an interface class for new threads - all you need to do is implement its {{Icode|run()}} function with the code that can be run concurrently. The runnable objects are added to the {{Icode|QThreadPool}} which allows the {{Icode|QRunnable}} objects to be re-used (this is more efficient than creating multiple threads).
    
− {{Icode|QThreadPool}} executes your code in a separate thread supporting execution of the same {{Icode|QRunnable}} more than once. + The first step is to implement the {{Icode|QRunnable}} interface:
−   + 
− == Multithread Image Loading == + 
− The first step is to implement  the {{Icode|QRunnable}} interface: + 
  <code cpp>   <code cpp>
  class LoadingThread : public QRunnable   class LoadingThread : public QRunnable
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  </code>   </code>
    
− The application has to wait until all threads finish their jobs. {{Icode|QThreadPool}} provides a method called {{Icode|waitForDone()'}} that does that. + The application has to wait until all threads finish their jobs. {{Icode|QThreadPool}} provides a method called {{Icode|waitForDone()}} that does that.
    
  <code cpp>   <code cpp>
  QThreadPool::globalInstance()->waitForDone();   QThreadPool::globalInstance()->waitForDone();
  </code>   </code>
  + 
  + == Summary ==
  + Multi-threading has enormously improved the performance of the [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] QML component by allowing the long running image save/load and initial processing steps to be carried out concurrently with image capture using the camera. Not only is the total execution time reduced, but the perceived behaviour is also better because the UI remains responsive to user input during calculation.
  + 
  + While multi-threading might not always provide a "real" improvement in execution time it is very useful in cases like this, where the different tasks don't need to use the same resources at the same time. Even where the total execution time remains the same, threading should be considered for its benefit of keeping the UI responsive. 
  + 
  + Using a {{Icode|QThreadPool}} and {{Icode|QRunnable}} is an efficient way to implement multi-threading on Qt as threads are created when needed and can be re-used.




Hugovk: Hugovk - Improved English and formatting
2012-05-27T15:41:37Z
Hugovk - Improved English and formatting

			
			
			
			
		
		← Older revision
		Revision as of 15:41, 27 May 2012
		
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  [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]]   [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]]
−  
  {{Note|This is an entry in the [[PureView Imaging Competition 2012Q2]]}}   {{Note|This is an entry in the [[PureView Imaging Competition 2012Q2]]}}
    
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  == Showcase  ==   == Showcase  ==
− [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] is a component component able to create [http://en.wikipedia.org/wiki/High_dynamic_range_imaging  High Dynamic Range images].<br /> + [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] is a component component able to create [http://en.wikipedia.org/wiki/High_dynamic_range_imaging  High Dynamic Range images].
− Basically to do that the component captures three photos at different exposure range mixing them using some algorithms. For further information, please referr to [http://www.developer.nokia.com/Community/Wiki/QHdrCamera_component_for_High_Dynamic_Range_Imaging this article].<br /> +  
− <br /> + Basically to do that the component captures three photos at different exposure range mixing them using some algorithms. For further information, please refer to [http://www.developer.nokia.com/Community/Wiki/QHdrCamera_component_for_High_Dynamic_Range_Imaging this article].
− The capture image in sequence have to be faster than possible. Heach time the QML component will be asked to shot a frame it saves in a default path the captured image and after is ready  to capture another frame.<br /> +  
− At the end of the three image capturing process, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.<br /> + Capturing images in sequence has to be done as fast as possible. Each time the QML component will be asked to shoot a frame it saves the captured image in the default path, after which it is ready to capture another frame.
− The loading process is very slow, expecially at resolution growing, due to the ( time of writing ) phone memory speed, so this has impacts the overall processing time. If during the next frame shooting application was able to begin the previous saved frame into memory this will reduce the waiting time, enhancing user experience.<br /> +  
− The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRUnnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html QThreadPool] class. + After the process of capturing three images, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.
  +  
  + The loading process is very slow, especially as resolution grows, due to the (at time of writing, May 2012) phone memory speed, so this impacts the overall processing time. If, during shooting the next frame, the application was also able to begin loading the previously saved frame into memory this will reduce the waiting time, enhancing user experience.
  +  
  + The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRunnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html QThreadPool] class.
    
  == QRunnable ==   == QRunnable ==
− The QRunnable class is an interface for representing a task or piece of code that needs to be executed, represented by your reimplementation of the run() function.<br /> + The {{Icode|QRunnable}} class is an interface for representing a task or piece of code that needs to be executed, represented by your reimplementation of the {{Icode|run()}} function.
− QThreadPool executes your code in a separate thread supporting execution of the same QRunnable more than once. +  
  + {{Icode|QThreadPool}} executes your code in a separate thread supporting execution of the same {{Icode|QRunnable}} more than once.
    
  == Multithread Image Loading ==   == Multithread Image Loading ==
− The first step is to implement  the QRunnable interface: + The first step is to implement  the {{Icode|QRunnable}} interface:
  <code cpp>   <code cpp>
  class LoadingThread : public QRunnable   class LoadingThread : public QRunnable
Line 73:
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  === QThreadPool ===   === QThreadPool ===
− The QML Camera component provide the {{Icode|onImageSaved ( path )}} signal, called after the image has been written to the filesystem, in this context connected to {{Icode|setShot}} SLOTs. Here we create the LoadingThread to start in background the into memory loading process. + The QML Camera component provides the {{Icode|onImageSaved ( path )}} signal, called after the image has been written to the filesystem, in this context connected to {{Icode|setShot}} slots. Here we create the {{Icode|LoadingThread}} to start memory loading process in the background.
    
  <code cpp>   <code cpp>
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  </code>   </code>
    
− Application have to wait until all threads finish their job. QThreadPool provide a method, called {{Icode|waitForDone()'}} to do that. + The application has to wait until all threads finish their jobs. {{Icode|QThreadPool}} provides a method called {{Icode|waitForDone()'}} that does that.
  +  
  <code cpp>   <code cpp>
  QThreadPool::globalInstance()->waitForDone();   QThreadPool::globalInstance()->waitForDone();
  </code>   </code>




Hugovk: Hugovk - /* Introduction */ Improved English
2012-05-27T15:27:26Z
Hugovk - - Introduction:  Improved English

			
			
			
			
		
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		Revision as of 15:27, 27 May 2012
		
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  == Introduction ==   == Introduction ==
− This article explains how to manage multithread into a mobile application.  [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] will be used as showcase. + This article explains how to manage multithreading in a mobile application.  [http://projects.developer.nokia.com/QHdrCamera/ QHdrCamera] will be used as a showcase.
    
  == Showcase  ==   == Showcase  ==



Galazzo: Galazzo -
2012-05-22T10:28:09Z
Galazzo -

			
			
			
			
		
		← Older revision
		Revision as of 10:28, 22 May 2012
		
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  [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]]   [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]]
  + 
  + {{Note|This is an entry in the [[PureView Imaging Competition 2012Q2]]}}
  + 
  {{ArticleMetaData <!-- v1.2 -->   {{ArticleMetaData <!-- v1.2 -->
  |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->   |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->



Galazzo: Galazzo -
2012-05-21T10:32:16Z
Galazzo -

			
			
			
			
		
		← Older revision
		Revision as of 10:32, 21 May 2012
		
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− [[Category:Draft]] + [[Category:Qt]][[Category:Symbian]][[Category:MeeGo]][[Category:Code Examples]]
  {{ArticleMetaData <!-- v1.2 -->   {{ArticleMetaData <!-- v1.2 -->
  |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->   |sourcecode= <!-- Link to example source code e.g. [[Media:The Code Example ZIP.zip]] -->
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  At the end of the three image capturing process, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.<br />   At the end of the three image capturing process, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.<br />
  The loading process is very slow, expecially at resolution growing, due to the ( time of writing ) phone memory speed, so this has impacts the overall processing time. If during the next frame shooting application was able to begin the previous saved frame into memory this will reduce the waiting time, enhancing user experience.<br />   The loading process is very slow, expecially at resolution growing, due to the ( time of writing ) phone memory speed, so this has impacts the overall processing time. If during the next frame shooting application was able to begin the previous saved frame into memory this will reduce the waiting time, enhancing user experience.<br />
− The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRUnnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html qthreadpool] class. + The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRUnnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html QThreadPool] class.
    
  == QRunnable ==   == QRunnable ==



Galazzo: Galazzo - /* QThreadPool */
2012-05-21T10:31:04Z
Galazzo - - QThreadPool

			
			
			
			
		
		← Older revision
		Revision as of 10:31, 21 May 2012
		
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  === QThreadPool ===   === QThreadPool ===
− The QML Camera component provide the ''onImageSaved ( path )'' signal, called after the image has been written to the filesystem, in this context connected to '''setSho'''''x'' SLOTs. + The QML Camera component provide the {{Icode|onImageSaved ( path )}} signal, called after the image has been written to the filesystem, in this context connected to {{Icode|setShot}} SLOTs. Here we create the LoadingThread to start in background the into memory loading process.
  +  
  <code cpp>   <code cpp>
  void QHdrCamera::setShot1(QString path) {   void QHdrCamera::setShot1(QString path) {
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  </code>   </code>
    
− ''Add categories below. Remove Category:Draft when the page is complete or near complete'' + Application have to wait until all threads finish their job. QThreadPool provide a method, called {{Icode|waitForDone()'}} to do that.
  + <code cpp>
  + QThreadPool::globalInstance()->waitForDone();
  + </code>




Galazzo: Galazzo -
2012-05-21T10:20:05Z
Galazzo -

			
			
			
			
		
		← Older revision
		Revision as of 10:20, 21 May 2012
		
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  The capture image in sequence have to be faster than possible. Heach time the QML component will be asked to shot a frame it saves in a default path the captured image and after is ready  to capture another frame.<br />   The capture image in sequence have to be faster than possible. Heach time the QML component will be asked to shot a frame it saves in a default path the captured image and after is ready  to capture another frame.<br />
  At the end of the three image capturing process, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.<br />   At the end of the three image capturing process, the flow process need to load all three photo into memory for the raw image processing to produce our HDR image.<br />
− The loading process is very slow, expecially at resolution growing, due to the ( time of writing ) phone memory speed, so this has impacts the overall processing time. If during the next frame shooting application was able to begin the previous saved frame into memory this will reduce the waiting time, enhancing user experience. + The loading process is very slow, expecially at resolution growing, due to the ( time of writing ) phone memory speed, so this has impacts the overall processing time. If during the next frame shooting application was able to begin the previous saved frame into memory this will reduce the waiting time, enhancing user experience.<br />
  + The solution provided uses [http://qt-project.org/doc/qt-4.8/qrunnable.html QRUnnable] interface and [http://qt-project.org/doc/qt-4.8/qthreadpool.html qthreadpool] class.
    
  + == QRunnable ==
  + The QRunnable class is an interface for representing a task or piece of code that needs to be executed, represented by your reimplementation of the run() function.<br />
  + QThreadPool executes your code in a separate thread supporting execution of the same QRunnable more than once.
  + 
  + == Multithread Image Loading ==
  + The first step is to implement  the QRunnable interface:
  + <code cpp>
  + class LoadingThread : public QRunnable
  + {
  + public:
  +     LoadingThread(QString*, QImage*);
  + 
  + private:
  +     QString* path;
  +     QImage* image;
  + 
  + protected:
  +     void run();
  + };
  + 
  + LoadingThread::LoadingThread(QString* path, QImage* image){
  +     this->path = path;
  +     this->image = image;
  + }
  + 
  + void LoadingThread::run()  {
  +     if( image->load(*path) ){
  +         qDebug() << "Image loaded";
  +     } else {
  +         qDebug() << "Error during image loading " << *path;
  +     }
  + }
  + </code>
  + 
  + === QThreadPool ===
  + The QML Camera component provide the ''onImageSaved ( path )'' signal, called after the image has been written to the filesystem, in this context connected to '''setSho'''''x'' SLOTs.
  + <code cpp>
  + void QHdrCamera::setShot1(QString path) {
  +     if( !QFile::rename(path, QDir::toNativeSeparators(s_shot1)) ) {
  +         qDebug() << "Impossible to rename shot1:" << path;
  +     } else {
  +         LoadingThread* tLoad = new LoadingThread(&s_shot1, &shot1);
  +         QThreadPool::globalInstance()->start(tLoad);
  +         emit savedShot1();
  +     }
  + }
  + 
  + void QHdrCamera::setShot2(QString path) {
  +     if( !QFile::rename(path, s_shot2) ) {
  +         qDebug() << "Impossible to rename shot2";
  +     } else {
  +         LoadingThread* tLoad = new LoadingThread(&s_shot2, &shot2);
  +         QThreadPool::globalInstance()->start(tLoad);
  +         emit savedShot2();
  +     }
  + }
  + 
  + void QHdrCamera::setShot3(QString path) {
  +     if( !QFile::rename(path, s_shot3) ){
  +         qDebug() << "Impossible to rename shot3";
  +     } else {
  +         LoadingThread* tLoad = new LoadingThread(&s_shot3, &shot3);
  +         QThreadPool::globalInstance()->start(tLoad);
  +         emit savedShot3();
  +     }
  + }
  + </code>
    
  ''Add categories below. Remove Category:Draft when the page is complete or near complete''   ''Add categories below. Remove Category:Draft when the page is complete or near complete''

How to add multithread support to your Qt application - Revision history

Hamishwillee: Text replace - "" to ""

Hamishwillee: Hamishwillee - Fix categories

Hamishwillee: Text replace - "Category:MeeGo" to "Category:MeeGo Harmattan"

Hamishwillee: Hamishwillee - Subedit. Fix categories. Restructure. Add cross links to other useful articles

Hugovk: Hugovk - Improved English and formatting

Hugovk: Hugovk - /* Introduction */ Improved English

Galazzo: Galazzo -

Galazzo: Galazzo -

Galazzo: Galazzo - /* QThreadPool */

Galazzo: Galazzo -

Hamishwillee: Text replace - "`" to ""`