Can't acquire semaphore in the function called by QtConcurrent::map

QSemaphore semaphore(1);

void worker(int value) {
    qDebug() << value << "entry";
    semaphore.acquire();
    semaphore.release();
    qDebug() << value << "exit";
}

void SemaphoreTest::bug() // A unit test function
{
    int count = 4;
    QList<int> input;
    for (int i = 0 ;i < count;i++) {
        input << i;
    }

    semaphore.acquire();

    QFuture<void> future = QtConcurrent::map(input, worker);

    QEventLoop loop;
    QTimer::singleShot(1000, [&]() {
        loop.quit();
    });
    loop.exec();

    qDebug() << "release semaphore in main thread";
    semaphore.release();

    QTRY_COMPARE(future.isFinished(), true);
}

// The order of number is not important
QDEBUG : SemaphoreTest::bug() 3 entry
QDEBUG : SemaphoreTest::bug() 0 entry
QDEBUG : SemaphoreTest::bug() 2 entry
QDEBUG : SemaphoreTest::bug() 1 entry
QDEBUG : SemaphoreTest::bug() release semaphore in main thread
QDEBUG : SemaphoreTest::bug() 0 exit
QDEBUG : SemaphoreTest::bug() 3 exit
QDEBUG : SemaphoreTest::bug() 2 exit
QDEBUG : SemaphoreTest::bug() 1 exit
PASS : SemaphoreTest::bug()

QDEBUG : SemaphoreTest::bug() 0 entry
QDEBUG : SemaphoreTest::bug() 1 entry
QDEBUG : SemaphoreTest::bug() 2 entry
QDEBUG : SemaphoreTest::bug() 3 entry
QDEBUG : SemaphoreTest::bug() release semaphore in main thread
QDEBUG : SemaphoreTest::bug() 0 exit
FAIL! : SemaphoreTest::bug() Compared values are not the same
Actual (((future.isFinished()))): 0
Expected (true) : 1
Loc: [../semaphore/tst_semaphoretest.cpp(52)]
PASS : SemaphoreTest::cleanupTestCase()