QThreadPool - Add method clear() to remove queued QRunnable.

QThreadPool::clear() method removes all queued QRunnable.

When a large number of long-running tasks are queud in a
QThreadPool its destruction, which calls waitForDone(), can
be quite long.
QThreadPool:clear() removes (and deletes when appropriate)
all QRunnable that have yet to be started from the queue
enabling a faster interruption.

Change-Id: Ie5d6028ad3cfe7e439d1db068c8d0936ff818db9
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp b/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
index fb34afb880..10a59ac301 100644
--- a/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
+++ b/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
@@ -97,6 +97,7 @@ private slots:
     void priorityStart_data();
     void priorityStart();
     void waitForDone();
+    void clear();
     void waitForDoneTimeout();
     void destroyingWaitsForTasksToFinish();
     void stressTest();
@@ -855,6 +856,34 @@ void tst_QThreadPool::waitForDoneTimeout()
     QVERIFY(threadPool.waitForDone(400));
 }
 
+void tst_QThreadPool::clear()
+{
+    QSemaphore sem(0);
+    class BlockingRunnable : public QRunnable
+    {
+        public:
+            QSemaphore & sem;
+            BlockingRunnable(QSemaphore & sem) : sem(sem){}
+            void run()
+            {
+                sem.acquire();
+                count.ref();
+            }
+    };
+
+    QThreadPool threadPool;
+    threadPool.setMaxThreadCount(10);
+    int runs = 2 * threadPool.maxThreadCount();
+    count.store(0);
+    for (int i = 0; i <= runs; i++) {
+        threadPool.start(new BlockingRunnable(sem));
+    }
+    threadPool.clear();
+    sem.release(threadPool.maxThreadCount());
+    threadPool.waitForDone();
+    QCOMPARE(count.load(), threadPool.maxThreadCount());
+}
+
 void tst_QThreadPool::destroyingWaitsForTasksToFinish()
 {
     QTime total, pass;