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Don't allow users to set maximum thread count for rendering to 1

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(This setting can sometimes unwantedly occur when using the same
profile across sessions of newer to very old QGIS versions)

The option is a misleading, as it's actually setting the global
thread limit for the entire QGIS application. If we allow this
to be set to a limit of 1 thread, then deadlocks
occur from the QImage internals in unpredictable ways.
This commit is contained in:
Nyall Dawson 2023-03-03 13:33:05 +10:00
parent 4dad60215a
commit 06b3678a57
4 changed files with 8 additions and 5 deletions
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2
python/core/auto_generated/qgsapplication.sip.in
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@ -695,7 +695,7 @@ Set maximum concurrent thread count
.. note::
must be between 1 and \#cores, -1 means use all available cores
must be between 2 and \#cores, -1 means use all available cores
.. versionadded:: 2.4
%End

4
src/app/options/qgsrenderingoptions.cpp
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@ -32,8 +32,8 @@ QgsRenderingOptionsWidget::QgsRenderingOptionsWidget( QWidget *parent )
QgsSettings settings;
chkAddedVisibility->setChecked( settings.value( QStringLiteral( "/qgis/new_layers_visible" ), true ).toBool() );
spinMaxThreads->setRange( 0, QThread::idealThreadCount() );
spinMaxThreads->setClearValue( 0, tr( "All Available (%1)" ).arg( QThread::idealThreadCount() ) );
spinMaxThreads->setRange( 1, QThread::idealThreadCount() );
spinMaxThreads->setClearValue( 1, tr( "All Available (%1)" ).arg( QThread::idealThreadCount() ) );
if ( QgsApplication::maxThreads() != -1 )
spinMaxThreads->setValue( QgsApplication::maxThreads() );
else

5
src/core/qgsapplication.cpp
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@ -2351,10 +2351,13 @@ void QgsApplication::setMaxThreads( int maxThreads )
QgsDebugMsgLevel( QStringLiteral( "maxThreads: %1" ).arg( maxThreads ), 2 );
// make sure value is between 1 and #cores, if not set to -1 (use #cores)
// 0 could be used to disable any parallel processing
if ( maxThreads < 1 || maxThreads > QThread::idealThreadCount() )
maxThreads = -1;
// force at least 2 threads -- anything less risks deadlocks within Qt itself (e.g in QImage internal mutexes)
if ( maxThreads > 0 && maxThreads < 2 )
maxThreads = 2;
// save value
ABISYM( sMaxThreads ) = maxThreads;

2
src/core/qgsapplication.h
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@ -670,7 +670,7 @@ class CORE_EXPORT QgsApplication : public QApplication
/**
* Set maximum concurrent thread count
* \note must be between 1 and \#cores, -1 means use all available cores
* \note must be between 2 and \#cores, -1 means use all available cores
* \since QGIS 2.4
*/
static void setMaxThreads( int maxThreads );