Do not multithread if already in a global threadpool thread

This can lead to a deadlock if we block all the worker threads, waiting
for the worker threads to finish.

Pick-to: 5.15
Fixes: QTBUG-84619
Change-Id: I92b7f96007897d86ece0c34223bab0df4ccbed9a
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/gui/image/qimage_conversions.cpp b/src/gui/image/qimage_conversions.cpp
index 357b936db9..134f17a9d1 100644
--- a/src/gui/image/qimage_conversions.cpp
+++ b/src/gui/image/qimage_conversions.cpp
@@ -237,14 +237,15 @@ void convert_generic(QImageData *dest, const QImageData *src, Qt::ImageConversio
     int segments = src->nbytes / (1<<16);
     segments = std::min(segments, src->height);
 
-    if (segments <= 1)
+    QThreadPool *threadPool = QThreadPool::globalInstance();
+    if (segments <= 1 || threadPool->contains(QThread::currentThread()))
         return convertSegment(0, src->height);
 
     QSemaphore semaphore;
     int y = 0;
     for (int i = 0; i < segments; ++i) {
         int yn = (src->height - y) / (segments - i);
-        QThreadPool::globalInstance()->start([&, y, yn]() {
+        threadPool->start([&, y, yn]() {
             convertSegment(y, y + yn);
             semaphore.release(1);
         });
@@ -291,14 +292,15 @@ void convert_generic_to_rgb64(QImageData *dest, const QImageData *src, Qt::Image
     int segments = src->nbytes / (1<<16);
     segments = std::min(segments, src->height);
 
-    if (segments <= 1)
+    QThreadPool *threadPool = QThreadPool::globalInstance();
+    if (segments <= 1 || threadPool->contains(QThread::currentThread()))
         return convertSegment(0, src->height);
 
     QSemaphore semaphore;
     int y = 0;
     for (int i = 0; i < segments; ++i) {
         int yn = (src->height - y) / (segments - i);
-        QThreadPool::globalInstance()->start([&, y, yn]() {
+        threadPool->start([&, y, yn]() {
             convertSegment(y, y + yn);
             semaphore.release(1);
         });
@@ -397,12 +399,13 @@ bool convert_generic_inplace(QImageData *data, QImage::Format dst_format, Qt::Im
 #ifdef QT_USE_THREAD_PARALLEL_IMAGE_CONVERSIONS
     int segments = data->nbytes / (1<<16);
     segments = std::min(segments, data->height);
-    if (segments > 1) {
+    QThreadPool *threadPool = QThreadPool::globalInstance();
+    if (segments > 1 && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;
         for (int i = 0; i < segments; ++i) {
             int yn = (data->height - y) / (segments - i);
-            QThreadPool::globalInstance()->start([&, y, yn]() {
+            threadPool->start([&, y, yn]() {
                 convertSegment(y, y + yn);
                 semaphore.release(1);
             });