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, 4 insertions, 3 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index 830ec6c4af..92a7d05dda 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -4786,15 +4786,16 @@ void QImage::applyColorTransform(const QColorTransform &transform)
         };
     }
 
-#if QT_CONFIG(thread)
+#if QT_CONFIG(thread) && !defined(Q_OS_WASM)
     int segments = sizeInBytes() / (1<<16);
     segments = std::min(segments, 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 = (height() - y) / (segments - i);
-            QThreadPool::globalInstance()->start([&, y, yn]() {
+            threadPool->start([&, y, yn]() {
                 transformSegment(y, y + yn);
                 semaphore.release(1);
             });