Add special thread pool for Qt Gui

To avoid gui slowdowns due to global pool being blocked.

Fixes: QTBUG-109511
Change-Id: I4e8d91e8fb0bd2e395072a082e992a3c5d3464ad
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 93047c71e8e6dd4ac28e1e59dcb561df11c759eb)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qcoreapplication.cpp

@@ -31,6 +31,7 @@
 #include <private/qthread_p.h>
 #if QT_CONFIG(thread)
 #include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 #endif
 #include <qelapsedtimer.h>
@@ -907,8 +908,10 @@ QCoreApplication::~QCoreApplication()
 #if QT_CONFIG(thread)
     // Synchronize and stop the global thread pool threads.
     QThreadPool *globalThreadPool = nullptr;
+    QThreadPool *guiThreadPool = nullptr;
     QT_TRY {
         globalThreadPool = QThreadPool::globalInstance();
+        guiThreadPool = QThreadPoolPrivate::qtGuiInstance();
     } QT_CATCH (...) {
         // swallow the exception, since destructors shouldn't throw
     }
@@ -916,6 +919,10 @@ QCoreApplication::~QCoreApplication()
         globalThreadPool->waitForDone();
         delete globalThreadPool;
     }
+    if (guiThreadPool) {
+        guiThreadPool->waitForDone();
+        delete guiThreadPool;
+    }
 #endif
 
 #ifndef QT_NO_QOBJECT

src/corelib/thread/qthreadpool.cpp

@@ -474,6 +474,21 @@ QThreadPool *QThreadPool::globalInstance()
     return theInstance;
 }
 
+/*!
+    Returns the QThreadPool instance for Qt Gui.
+    \internal
+*/
+QThreadPool *QThreadPoolPrivate::qtGuiInstance()
+{
+    Q_CONSTINIT static QPointer<QThreadPool> guiInstance;
+    Q_CONSTINIT static QBasicMutex theMutex;
+
+    const QMutexLocker locker(&theMutex);
+    if (guiInstance.isNull() && !QCoreApplication::closingDown())
+        guiInstance = new QThreadPool();
+    return guiInstance;
+}
+
 /*!
     Reserves a thread and uses it to run \a runnable, unless this thread will
     make the current thread count exceed maxThreadCount().  In that case,

src/corelib/thread/qthreadpool_p.h

@@ -134,6 +134,8 @@ public:
     void stealAndRunRunnable(QRunnable *runnable);
     void deletePageIfFinished(QueuePage *page);
 
+    static QThreadPool *qtGuiInstance();
+
     mutable QMutex mutex;
     QSet<QThreadPoolThread *> allThreads;
     QQueue<QThreadPoolThread *> waitingThreads;

src/gui/image/qimage.cpp

@@ -35,8 +35,9 @@
 #include <private/qfont_p.h>
 
 #if QT_CONFIG(thread)
-#include "qsemaphore.h"
-#include "qthreadpool.h"
+#include <qsemaphore.h>
+#include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 
 #include <qtgui_tracepoints_p.h>
@@ -5119,7 +5120,7 @@ void QImage::applyColorTransform(const QColorTransform &transform)
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
     int segments = (qsizetype(width()) * height()) >> 16;
     segments = std::min(segments, height());
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;

src/gui/image/qimage_conversions.cpp

@@ -15,6 +15,7 @@
 #if QT_CONFIG(thread)
 #include <qsemaphore.h>
 #include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #ifdef Q_OS_WASM
 // WebAssembly has threads; however we can't block the main thread.
 #else
@@ -203,7 +204,7 @@ void convert_generic(QImageData *dest, const QImageData *src, Qt::ImageConversio
     int segments = (qsizetype(src->width) * src->height) >> 16;
     segments = std::min(segments, src->height);
 
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments <= 1 || !threadPool || threadPool->contains(QThread::currentThread()))
         return convertSegment(0, src->height);
 
@@ -258,7 +259,7 @@ void convert_generic_over_rgb64(QImageData *dest, const QImageData *src, Qt::Ima
     int segments = (qsizetype(src->width) * src->height) >> 16;
     segments = std::min(segments, src->height);
 
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments <= 1 || !threadPool || threadPool->contains(QThread::currentThread()))
         return convertSegment(0, src->height);
 
@@ -312,7 +313,7 @@ void convert_generic_over_rgba32f(QImageData *dest, const QImageData *src, Qt::I
     int segments = (qsizetype(src->width) * src->height) >> 16;
     segments = std::min(segments, src->height);
 
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments <= 1 || !threadPool || threadPool->contains(QThread::currentThread()))
         return convertSegment(0, src->height);
 
@@ -419,7 +420,7 @@ bool convert_generic_inplace(QImageData *data, QImage::Format dst_format, Qt::Im
 #ifdef QT_USE_THREAD_PARALLEL_IMAGE_CONVERSIONS
     int segments = (qsizetype(data->width) * data->height) >> 16;
     segments = std::min(segments, data->height);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;
@@ -513,7 +514,7 @@ bool convert_generic_inplace_over_rgb64(QImageData *data, QImage::Format dst_for
 #ifdef QT_USE_THREAD_PARALLEL_IMAGE_CONVERSIONS
     int segments = (qsizetype(data->width) * data->height) >> 16;
     segments = std::min(segments, data->height);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;
@@ -608,7 +609,7 @@ bool convert_generic_inplace_over_rgba32f(QImageData *data, QImage::Format dst_f
 #ifdef QT_USE_THREAD_PARALLEL_IMAGE_CONVERSIONS
     int segments = (qsizetype(data->width) * data->height) >> 16;
     segments = std::min(segments, data->height);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;

src/gui/painting/qdrawhelper.cpp

@@ -32,6 +32,7 @@
 #if defined(QT_USE_THREAD_PARALLEL_FILLS)
 #include <qsemaphore.h>
 #include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 
 QT_BEGIN_NAMESPACE
@@ -3777,7 +3778,7 @@ static void spanfill_from_first(QRasterBuffer *rasterBuffer, QPixelLayout::BPP b
 #if defined(QT_USE_THREAD_PARALLEL_FILLS)
 #define QT_THREAD_PARALLEL_FILLS(function) \
     const int segments = (count + 32) / 64; \
-    QThreadPool *threadPool = QThreadPool::globalInstance(); \
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance(); \
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) { \
         QSemaphore semaphore; \
         int c = 0; \
@@ -3786,7 +3787,7 @@ static void spanfill_from_first(QRasterBuffer *rasterBuffer, QPixelLayout::BPP b
             threadPool->start([&, c, cn]() { \
                 function(c, c + cn); \
                 semaphore.release(1); \
-            }); \
+            }, 1); \
             c += cn; \
         } \
         semaphore.acquire(segments); \

src/gui/painting/qimagescale.cpp

@@ -10,8 +10,9 @@
 #include "qrgbafloat.h"
 
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
-#include "qsemaphore.h"
-#include "qthreadpool.h"
+#include <qsemaphore.h>
+#include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 
 QT_BEGIN_NAMESPACE
@@ -273,7 +274,7 @@ static inline void multithread_pixels_function(QImageScaleInfo *isi, int dh, con
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
     int segments = (qsizetype(isi->sh) * isi->sw) / (1<<16);
     segments = std::min(segments, dh);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;

src/gui/painting/qimagescale_neon.cpp

@@ -6,8 +6,9 @@
 #include <private/qsimd_p.h>
 
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
-#include "qsemaphore.h"
-#include "qthreadpool.h"
+#include <qsemaphore.h>
+#include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 
 #if defined(__ARM_NEON__)
@@ -22,7 +23,7 @@ static inline void multithread_pixels_function(QImageScaleInfo *isi, int dh, con
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
     int segments = (qsizetype(isi->sh) * isi->sw) / (1<<16);
     segments = std::min(segments, dh);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;

src/gui/painting/qimagescale_sse4.cpp

@@ -7,8 +7,9 @@
 #include <private/qsimd_p.h>
 
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
-#include "qsemaphore.h"
-#include "qthreadpool.h"
+#include <qsemaphore.h>
+#include <qthreadpool.h>
+#include <private/qthreadpool_p.h>
 #endif
 
 #if defined(QT_COMPILER_SUPPORTS_SSE4_1)
@@ -23,7 +24,7 @@ static inline void multithread_pixels_function(QImageScaleInfo *isi, int dh, con
 #if QT_CONFIG(thread) && !defined(Q_OS_WASM)
     int segments = (qsizetype(isi->sh) * isi->sw) / (1<<16);
     segments = std::min(segments, dh);
-    QThreadPool *threadPool = QThreadPool::globalInstance();
+    QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance();
     if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) {
         QSemaphore semaphore;
         int y = 0;