#include <QtCore>
#include <qt_windows.h>

int fooCallCounter = 0;
void foo() { fooCallCounter++; }

int main(int argc, char *argv[])
{
    QThreadPool::globalInstance()->setMaxThreadCount(1);
    QThreadPool::globalInstance()->setExpiryTimeout(1000);
    
    qDebug() << "Beginning: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 0 == allThreads(0) - expiredThreads(0) - waitingThreads(0) + reservedThreads(0)
    
    QThreadPool::globalInstance()->reserveThread(); // reservedThreads++
    qDebug() << "After Step 1: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount();  // activeThreadCount == 1 == allThreads(0) - expiredThreads(0) - waitingThreads(0) + reservedThreads(1)
    
    QtConcurrent::run(&foo); // allThreads gains a thread
    qDebug() << "After Step 2: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 2 == allThreads(1) - expiredThreads(0) - waitingThreads(0) + reservedThreads(1)
    
    ::Sleep(100); // finish concurrent, waitingThreads++
    qDebug() << "After Step 3: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 1 == allThreads(1) - expiredThreads(0) - waitingThreads(1) + reservedThreads(1)
    
    // In the next QtConcurrent::run(...), QThreadPoolPrivate tryStart will not succeed b/c 
    //     activeThreadCount() >= maxThreadCount() (
    //     Because tryStart doesn't succeed, the waitingThread count will not be decreased.
    // B/c tryStart doesn't succeed, enqueueTask will be called. EnqueueTask will call wakeOne. wakeOne will wake
    //     the one waiting thread. However, the waitingThread count will not be decreased. 
    QtConcurrent::run(&foo); 
    qDebug() << "After Step 4: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 1 == allThreads(1) - expiredThreads(0) - waitingThreads(1) + reservedThreads(1)
    
    // Once the second QtConcurrent::run(...) completes, the thread will start waiting again, increasing the waitingThread count. 
    
    ::Sleep(100); // finish concurrent, waitingThread++
    qDebug() << "After Step 5: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 0 == allThreads(1) - expiredThreads(0) - waitingThreads(2) + reservedThreads(1)
    
    QThreadPool::globalInstance()->releaseThread(); // reservedThreads--
    qDebug() << "After Step 6/Problem state: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == -1 == allThreads(1) - expiredThreads(0) - waitingThreads(2) + reservedThreads(0)

    ::Sleep(1500); // finish concurrent, waitingThread++
    qDebug() << "After expiry: ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == -1 == allThreads(1) - expiredThreads(1) - waitingThreads(1) + reservedThreads(0)

    
    // In the next QtConcurrent::run(...), QThreadPool thinks there is a thread waiting to be used
    // and so will decrement the waitingThreads count, and then enqueue the task (thus calling wakeOne()). 
    // However, there are no threads actually running/waiting, and so nothing will happen. 
    QtConcurrent::run(&foo); 
    ::Sleep(500); 
    
    if (fooCallCounter != 3) {
        qDebug() << "Foo was not called the third time. fooCallCounter:" << fooCallCounter;
    }
    
    qDebug() << "Before forth call to run(): ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 0 == allThreads(1) - expiredThreads(1) - waitingThreads(0) + reservedThreads(0)
    
    // Now that waitingThreads is back to the correct value, we can start new tasks again. BOTH calls to foo should be run now.
    QtConcurrent::run(&foo); 
    ::Sleep(500); 
    if (fooCallCounter != 4) {
        qDebug() << "Unexpected value for fooCallCounter:" << fooCallCounter;
    }
    
    qDebug() << "After forth call to run(): ThreadPool.activeThreadCount():" << QThreadPool:: globalInstance()->activeThreadCount(); // activeThreadCount == 0 == allThreads(1) - expiredThreads(0) - waitingThreads(1) + reservedThreads(0)

	return 0;
}