[WFS provider] Fix deadlock when adding WFS layer to project from Python console (fixes #17087)

rouault · rouault · commit 505e36599296 · 2017-11-09T13:00:35.000+01:00
diff --git a/src/providers/wfs/qgswfsfeatureiterator.cpp b/src/providers/wfs/qgswfsfeatureiterator.cpp
@@ -759,11 +759,25 @@ void QgsWFSThreadedFeatureDownloader::stop()
   }
 }
 
+void QgsWFSThreadedFeatureDownloader::startAndWait()
+{
+  start();
+
+  QMutexLocker locker( &mWaitMutex );
+  while ( !mDownloader )
+  {
+    mWaitCond.wait( &mWaitMutex );
+  }
+}
+
 void QgsWFSThreadedFeatureDownloader::run()
 {
   // We need to construct it in the run() method (i.e. in the new thread)
   mDownloader = new QgsWFSFeatureDownloader( mShared );
-  emit ready();
+  {
+    QMutexLocker locker( &mWaitMutex );
+    mWaitCond.wakeOne();
+  }
   mDownloader->run( true, /* serialize features */
                     0 /* user max features */ );
 }
diff --git a/src/providers/wfs/qgswfsfeatureiterator.h b/src/providers/wfs/qgswfsfeatureiterator.h
@@ -24,6 +24,8 @@
 
 #include <QProgressDialog>
 #include <QPushButton>
+#include <QMutex>
+#include <QWaitCondition>
 
 class QgsWFSProvider;
 class QgsWFSSharedData;
@@ -164,20 +166,20 @@ class QgsWFSThreadedFeatureDownloader: public QThread
     /** Return downloader object */
     QgsWFSFeatureDownloader* downloader() { return mDownloader; }
 
-    /** Stops (synchronously) the download */
-    void stop();
-
-  signals:
-    /** Emitted when the thread is ready */
-    void ready();
+    //! Starts thread and wait for it to be started
+    void startAndWait();
 
+    //! Stops (synchronously) the download
+    void stop();
   protected:
     /** Inherited from QThread. Starts the download */
     void run() override;
 
   private:
     QgsWFSSharedData* mShared;  //!< Mutable data shared between provider and feature sources
     QgsWFSFeatureDownloader* mDownloader;
+    QWaitCondition mWaitCond;
+    QMutex mWaitMutex;
 };
 
 class QgsWFSFeatureSource;
diff --git a/src/providers/wfs/qgswfsshareddata.cpp b/src/providers/wfs/qgswfsshareddata.cpp
@@ -553,10 +553,7 @@ int QgsWFSSharedData::registerToCache( QgsWFSFeatureIterator* iterator, QgsRecta
     mDownloadFinished = false;
     mComputedExtent = QgsRectangle();
     mDownloader = new QgsWFSThreadedFeatureDownloader( this );
-    QEventLoop loop;
-    connect( mDownloader, SIGNAL( ready() ), &loop, SLOT( quit() ) );
-    mDownloader->start();
-    loop.exec( QEventLoop::ExcludeUserInputEvents );
+    mDownloader->startAndWait();
   }
   if ( mDownloadFinished )
     return -1;
