QMutex 類

The QMutex class provides access serialization between threads. 更多...

頭：	#include <QMutex>

注意： 此類的所有函數綫程安全 .

公共類型

enum	RecursionMode { Recursive, NonRecursive }

公共函數

	QMutex (RecursionMode mode = NonRecursive)
	~QMutex ()
void	lock ()
bool	tryLock ()
bool	tryLock (int timeout )
void	unlock ()

詳細描述

The QMutex class provides access serialization between threads.

The purpose of a QMutex is to protect an object, data structure or section of code so that only one thread can access it at a time (this is similar to the Java synchronized 關鍵詞)。通常使用互斥最好采用 QMutexLocker 因為這使之能輕鬆確保鎖定和解鎖的一緻履行。

例如，假定有方法每 2 行嚮用戶打印消息：

int number = 6;
void method1()
{
    number *= 5;
    number /= 4;
}
void method2()
{
    number *= 3;
    number /= 2;
}

若連續調用這 2 方法，會發生以下：

// method1()
number *= 5;        // number is now 30
number /= 4;        // number is now 7
// method2()
number *= 3;        // number is now 21
number /= 2;        // number is now 10

若從 2 綫程同時調用這 2 方法，就會産生以下序列：

// Thread 1 calls method1()
number *= 5;        // number is now 30
// Thread 2 calls method2().
//
// Most likely Thread 1 has been put to sleep by the operating
// system to allow Thread 2 to run.
number *= 3;        // number is now 90
number /= 2;        // number is now 45
// Thread 1 finishes executing.
number /= 4;        // number is now 11, instead of 10

若添加互斥，應該獲得希望結果：

QMutex mutex;
int number = 6;
void method1()
{
    mutex.lock();
    number *= 5;
    number /= 4;
    mutex.unlock();
}
void method2()
{
    mutex.lock();
    number *= 3;
    number /= 2;
    mutex.unlock();
}

那麼僅一綫程可以修改 編號 在任何給定時間且結果是正確的。當然，這是通俗範例，但適用於事情需要按特定序列發生的任何其它情況。

當調用 lock () 在綫程中，其它綫程試著調用 lock () 在同一位置將阻塞，直到綫程獲得鎖調用 unlock ()。非阻塞替代 lock () 是 tryLock ().

另請參閱 QMutexLocker , QReadWriteLock , QSemaphore ，和 QWaitCondition .

成員類型文檔編製

enum QMutex:: RecursionMode

常量	值	描述
`QMutex::Recursive`	`1`	In this mode, a thread can lock the same mutex multiple times and the mutex won't be unlocked until a corresponding number of unlock () 調用已做齣。
`QMutex::NonRecursive`	`0`	In this mode, a thread may only lock a mutex once.

另請參閱 QMutex ().

成員函數文檔編製

QMutex:: QMutex ( RecursionMode mode = NonRecursive)

構造新的互斥。互斥是在解鎖狀態下創建的。

若 mode is QMutex::Recursive , a thread can lock the same mutex multiple times and the mutex won't be unlocked until a corresponding number of unlock () calls have been made. The default is QMutex::NonRecursive .

另請參閱 lock () 和 unlock ().

QMutex:: ~QMutex ()

銷毀互斥。

警告： 銷毀鎖定互斥可能導緻未定義行為。

void QMutex:: lock ()

Locks the mutex. If another thread has locked the mutex then this call will block until that thread has unlocked it.

Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a 遞歸互斥。若此互斥是非遞歸互斥，此函數將 dead-lock when the mutex is locked recursively.

另請參閱 unlock ().

bool QMutex:: tryLock ()

Attempts to lock the mutex. If the lock was obtained, this function returns true. If another thread has locked the mutex, this function returns false immediately.

If the lock was obtained, the mutex must be unlocked with unlock () 在另一綫程可以成功鎖定它之前。

Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a 遞歸互斥。若此互斥是非遞歸互斥，此函數將 always return false when attempting to lock the mutex recursively.

另請參閱 lock () 和 unlock ().

bool QMutex:: tryLock ( int timeout )

這是重載函數。

Attempts to lock the mutex. This function returns true if the lock was obtained; otherwise it returns false. If another thread has locked the mutex, this function will wait for at most timeout milliseconds for the mutex to become available.

注意：傳遞負數作為 timeout 相當於調用 lock (), i.e. this function will wait forever until mutex can be locked if timeout 為負。

If the lock was obtained, the mutex must be unlocked with unlock () 在另一綫程可以成功鎖定它之前。

另請參閱 lock () 和 unlock ().

void QMutex:: unlock ()

Unlocks the mutex. Attempting to unlock a mutex in a different thread to the one that locked it results in an error. Unlocking a mutex that is not locked results in undefined behavior.

另請參閱 lock ().