Fix race condition causing crash on startup

nyalldawson · nyalldawson · commit 1f02b42e04c0 · 2018-10-08T11:20:40.000+10:00
Also flick more static list initializations across to nicer
std::call_once implimentations
diff --git a/src/core/qgsdataitem.cpp b/src/core/qgsdataitem.cpp
@@ -1334,10 +1334,11 @@ void QgsZipItem::init()
   mIconName = QStringLiteral( "/mIconZip.svg" );
   mVsiPrefix = vsiPrefix( mFilePath );
 
-  if ( sProviderNames.isEmpty() )
+  static std::once_flag initialized;
+  std::call_once( initialized, [ = ]
   {
     sProviderNames << QStringLiteral( "OGR" ) << QStringLiteral( "GDAL" );
-  }
+  } );
 }
 
 QVector<QgsDataItem *> QgsZipItem::createChildren()
diff --git a/src/core/qgsvectordataprovider.cpp b/src/core/qgsvectordataprovider.cpp
@@ -33,6 +33,7 @@
 #include "qgslogger.h"
 #include "qgsmessagelog.h"
 #include "qgssettings.h"
+#include <mutex>
 
 QgsVectorDataProvider::QgsVectorDataProvider( const QString &uri, const ProviderOptions &options )
   : QgsDataProvider( uri, options )
@@ -605,7 +606,8 @@ static bool _compareEncodings( const QString &s1, const QString &s2 )
 
 QStringList QgsVectorDataProvider::availableEncodings()
 {
-  if ( sEncodings.isEmpty() )
+  static std::once_flag initialized;
+  std::call_once( initialized, [ = ]
   {
     Q_FOREACH ( const QString &codec, QTextCodec::availableCodecs() )
     {
@@ -658,10 +660,11 @@ QStringList QgsVectorDataProvider::availableEncodings()
     smEncodings << "TIS-620";
     smEncodings << "System";
 #endif
-  }
 
-  // Do case-insensitive sorting of encodings
-  std::sort( sEncodings.begin(), sEncodings.end(), _compareEncodings );
+    // Do case-insensitive sorting of encodings
+    std::sort( sEncodings.begin(), sEncodings.end(), _compareEncodings );
+
+  } );
 
   return sEncodings;
 }
diff --git a/src/providers/gdal/qgsgdaldataitems.cpp b/src/providers/gdal/qgsgdaldataitems.cpp
@@ -184,18 +184,13 @@ QgsDataItem *QgsGdalDataItemProvider::createDataItem( const QString &pathIn, Qgs
     return nullptr;
 
   // get supported extensions
-  if ( sExtensions.isEmpty() )
+  static std::once_flag initialized;
+  std::call_once( initialized, [ = ]
   {
-    // this code may be executed by more threads at once!
-    // use a mutex to make sure this does not happen (so there's no crash on start)
-    QMutexLocker locker( &sBuildingFilters );
-    if ( sExtensions.isEmpty() )
-    {
-      buildSupportedRasterFileFilterAndExtensions( sFilterString, sExtensions, sWildcards );
-      QgsDebugMsgLevel( "extensions: " + sExtensions.join( " " ), 2 );
-      QgsDebugMsgLevel( "wildcards: " + sWildcards.join( " " ), 2 );
-    }
-  }
+    buildSupportedRasterFileFilterAndExtensions( sFilterString, sExtensions, sWildcards );
+    QgsDebugMsgLevel( "extensions: " + sExtensions.join( " " ), 2 );
+    QgsDebugMsgLevel( "wildcards: " + sWildcards.join( " " ), 2 );
+  } );
 
   // skip *.aux.xml files (GDAL auxiliary metadata files),
   // *.shp.xml files (ESRI metadata) and *.tif.xml files (TIFF metadata)
diff --git a/src/providers/mdal/qgsmdaldataitems.cpp b/src/providers/mdal/qgsmdaldataitems.cpp
@@ -60,8 +60,8 @@ QGISEXTERN QgsDataItem *dataItem( QString path, QgsDataItem *parentItem )
   if ( !info.isFile() )
     return nullptr;
 
-  // get supported extensions
-  if ( sExtensions.isEmpty() )
+  static std::once_flag initialized;
+  std::call_once( initialized, [ = ]( )
   {
     // TODO ask MDAL for extensions !
     sExtensions << QStringLiteral( "2dm" )
@@ -72,7 +72,7 @@ QGISEXTERN QgsDataItem *dataItem( QString path, QgsDataItem *parentItem )
                 << QStringLiteral( "grib1" )
                 << QStringLiteral( "grib2" )
                 << QStringLiteral( "nc" );
-  }
+  } );
 
   // Filter files by extension
   if ( !sExtensions.contains( suffix ) )

Original file line number	Diff line number	Diff line change
`@@ -1334,10 +1334,11 @@ void QgsZipItem::init()`
`1334`	`1334`	`mIconName = QStringLiteral( "/mIconZip.svg" );`
`1335`	`1335`	`mVsiPrefix = vsiPrefix( mFilePath );`
`1336`	`1336`
`1337`		`- if ( sProviderNames.isEmpty() )`
	`1337`	`+ static std::once_flag initialized;`
	`1338`	`+ std::call_once( initialized, [ = ]`
`1338`	`1339`	`{`
`1339`	`1340`	`sProviderNames << QStringLiteral( "OGR" ) << QStringLiteral( "GDAL" );`
`1340`		`- }`
	`1341`	`+ } );`
`1341`	`1342`	`}`
`1342`	`1343`
`1343`	`1344`	`QVector<QgsDataItem *> QgsZipItem::createChildren()`