QThreadPool::cancel() to remove individual jobs from the job queue.

[ChangeLog][QtCore][QThreadPool] Added QThreadPool::cancel() which allows
removing from the job queue a job that hasn't been started yet.

Change-Id: Ib8f1c1f32a34f5eec8338c641d820b928e470164
Reviewed-by: Nick Shaforostoff <shafff@ukr.net>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp b/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
index 9c2c8bf12a..1f1cf1db0c 100644
--- a/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
+++ b/tests/auto/corelib/thread/qthreadpool/tst_qthreadpool.cpp
@@ -92,6 +92,7 @@ private slots:
     void priorityStart();
     void waitForDone();
     void clear();
+    void cancel();
     void waitForDoneTimeout();
     void destroyingWaitsForTasksToFinish();
     void stressTest();
@@ -958,6 +959,56 @@ void tst_QThreadPool::clear()
     QCOMPARE(count.load(), threadPool.maxThreadCount());
 }
 
+void tst_QThreadPool::cancel()
+{
+    QSemaphore sem(0);
+    class BlockingRunnable : public QRunnable
+    {
+    public:
+        QSemaphore & sem;
+        int & dtorCounter;
+        int & runCounter;
+        int dummy;
+        BlockingRunnable(QSemaphore & s, int & c, int & r) : sem(s), dtorCounter(c), runCounter(r){}
+        ~BlockingRunnable(){dtorCounter++;}
+        void run()
+        {
+            runCounter++;
+            sem.acquire();
+            count.ref();
+        }
+    };
+    typedef BlockingRunnable* BlockingRunnablePtr;
+
+    QThreadPool threadPool;
+    threadPool.setMaxThreadCount(3);
+    int runs = 2 * threadPool.maxThreadCount();
+    BlockingRunnablePtr* runnables = new BlockingRunnablePtr[runs];
+    count.store(0);
+    int dtorCounter = 0;
+    int runCounter = 0;
+    for (int i = 0; i < runs; i++) {
+        runnables[i] = new BlockingRunnable(sem, dtorCounter, runCounter);
+        runnables[i]->setAutoDelete(i != 0 && i != (runs-1)); //one which will run and one which will not
+        threadPool.cancel(runnables[i]); //verify NOOP for jobs not in the queue
+        threadPool.start(runnables[i]);
+    }
+    for (int i = 0; i < runs; i++) {
+        threadPool.cancel(runnables[i]);
+    }
+    runnables[0]->dummy = 0; //valgrind will catch this if cancel() is crazy enough to delete currently running jobs
+    runnables[runs-1]->dummy = 0;
+    QCOMPARE(dtorCounter, runs-threadPool.maxThreadCount()-1);
+    sem.release(threadPool.maxThreadCount());
+    threadPool.waitForDone();
+    QCOMPARE(runCounter, threadPool.maxThreadCount());
+    QCOMPARE(count.load(), threadPool.maxThreadCount());
+    QCOMPARE(dtorCounter, runs-2);
+    delete runnables[0]; //if the pool deletes them then we'll get double-free crash
+    delete runnables[runs-1];
+    delete[] runnables;
+}
+
 void tst_QThreadPool::destroyingWaitsForTasksToFinish()
 {
     QTime total, pass;