內容

公共類型
公共函數
詳細描述

QMutex 類

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

頭：	#include <QMutex>
qmake:	QT += core
繼承：	QBasicMutex

所有成員列錶，包括繼承成員

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 (QMutex::RecursionMode mode = NonRecursive)
	~QMutex ()
bool	isRecursive () const
void	lock ()
bool	tryLock (int timeout = 0)
bool	try_lock ()
bool	try_lock_for (std::chrono::duration<Rep, Period> duration )
bool	try_lock_until (std::chrono::time_point<Clock, Duration> timePoint )
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 ().

QMutex is optimized to be fast in the non-contended case. A non-recursive QMutex will not allocate memory if there is no contention on that mutex. It is constructed and destroyed with almost no overhead, which means it is fine to have many mutexes as part of other classes.

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 ( 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. Otherwise a thread may only lock a mutex once. The default is QMutex::NonRecursive .

Recursive mutexes are slower and take more memory than non-recursive ones.

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。

bool QMutex:: isRecursive () const

返迴 true 若互斥是遞歸的。

該函數在 Qt 5.7 引入。

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 ( int timeout = 0)

試圖鎖定互斥。此函數返迴 true 若獲得鎖；否則返迴 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。

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:: try_lock ()

試圖鎖定互斥。此函數返迴 true 若獲得鎖；否則返迴 false .

提供此函數是為兼容標準庫概念 Lockable 。它相當於 tryLock ().

函數返迴 true 若獲得鎖；否則返迴 false

該函數在 Qt 5.8 引入。

bool QMutex:: try_lock_for ( std::chrono::duration < Rep , Period > duration )

試圖鎖定互斥。此函數返迴 true 若獲得鎖；否則返迴 false 。若另一綫程有鎖定互斥，此函數將等待至少 duration 為使互斥變得可用。

注意：傳遞負值持續時間作為 duration 相當於調用 try_lock ()。此行為不同於 tryLock ().

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。

該函數在 Qt 5.8 引入。

另請參閱 lock () 和 unlock ().

bool QMutex:: try_lock_until ( std::chrono::time_point < Clock , Duration > timePoint )

試圖鎖定互斥。此函數返迴 true 若獲得鎖；否則返迴 false . If another thread has locked the mutex, this function will wait at least until timePoint 為使互斥變得可用。

注意：傳遞 timePoint which has already passed is equivalent to calling try_lock ()。此行為不同於 tryLock ().

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。

該函數在 Qt 5.8 引入。

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 ().