Reintroducing and fixing an event loop to wait for task starting

rldhont · rldhont · commit c184270ebe2b · 2020-05-27T09:24:22.000+02:00
The method QgsTask::waitForFinished doesn't wait the task to be finished if the task has not yet being started (because the task wait to start if there is no thread available for instance). This bug has been fixed in a much nicer way in version 3.12 and upper, but it has not been backported to version 3.10. If #32838 is backported, for example with #36651, this commit has to be revert.
diff --git a/src/core/qgsabstractcontentcache.h b/src/core/qgsabstractcontentcache.h
@@ -463,6 +463,19 @@ class CORE_EXPORT QgsAbstractContentCache : public QgsAbstractContentCacheBase
      */
     bool waitForTaskFinished( QgsNetworkContentFetcherTask *task ) const
     {
+      // First step, waiting for task running
+      bool waitForTaskBegun = ( task->status() != QgsTask::Running
+                                && task->status() != QgsTask::Complete
+                                && task->status() != QgsTask::Terminated );
+      if ( waitForTaskBegun )
+      {
+        QEventLoop loop;
+        connect( task, &QgsNetworkContentFetcherTask::begun, &loop, &QEventLoop::quit );
+        if ( waitForTaskBegun )
+          loop.exec();
+      }
+
+      // Second step, wait for task finished
       // Wait up to timeout seconds for task finished
       if ( task->waitForFinished( QgsNetworkAccessManager::timeout() ) )
       {
