QSemaphore ¶

概要 ¶

详细描述 ¶

A semaphore is a generalization of a mutex. While a mutex can only be locked once, it’s possible to acquire a semaphore multiple times. Semaphores are typically used to protect a certain number of identical resources.

信号量支持 2 基础操作 acquire() and release() :

• acquire( n ) 试着获得 n resources. If there aren’t that many resources available, the call will block until this is the case.

• release( n ) 释放 n 资源。

There’s also a tryAcquire() function that returns immediately if it cannot acquire the resources, and an available() function that returns the number of available resources at any time.

范例：

sem = QSemaphore(5)      # sem.available() == 5
sem.acquire(3)           # sem.available() == 2
sem.acquire(2)           # sem.available() == 0
sem.release(5)           # sem.available() == 5
sem.release(5)           # sem.available() == 10
sem.tryAcquire(1)        # sem.available() == 9, returns true
sem.tryAcquire(250)      # sem.available() == 9, returns false
											

信号量的典型应用程序是用于控制由生产者线程和消费者线程共享的循环缓冲的访问。 信号量范例 shows how to use QSemaphore to solve that problem.

信号量的非计算范例是在餐馆用餐。采用餐厅中的椅子数初始信号量。当人们到达时，他们想要座位。由于座无虚席， available() is decremented. As people leave, the available() is incremented, allowing more people to enter. If a party of 10 people want to be seated, but there are only 9 seats, those 10 people will wait, but a party of 4 people would be seated (taking the available seats to 5, making the party of 10 people wait longer).

另请参阅

QSemaphoreReleaser QMutex QWaitCondition QThread 信号量范例

class QSemaphore ( [ n=0 ] ) ¶

param n

int

Creates a new semaphore and initializes the number of resources it guards to n (by default, 0).

另请参阅

release() available()

PySide2.QtCore.QSemaphore. acquire ( [ n=1 ] ) ¶

参数

n – int

Tries to acquire n resources guarded by the semaphore. If n > available() , this call will block until enough resources are available.

另请参阅

release() available() tryAcquire()

PySide2.QtCore.QSemaphore. available ( ) ¶

返回类型

int

Returns the number of resources currently available to the semaphore. This number can never be negative.

另请参阅

acquire() release()

PySide2.QtCore.QSemaphore. release ( [ n=1 ] ) ¶

参数

n – int

发行 n resources guarded by the semaphore.

This function can be used to “create” resources as well. For example:

sem = QSemaphore(5)     # a semaphore that guards 5 resources
sem.acquire(5)          # acquire all 5 resources
sem.release(5)          # release the 5 resources
sem.release(10)         # "create" 10 new resources
											

QSemaphoreReleaser 是 RAII wrapper around this function.

另请参阅

acquire() available() QSemaphoreReleaser

PySide2.QtCore.QSemaphore. tryAcquire ( [ n=1 ] ) ¶

参数

n – int

返回类型

bool

Tries to acquire n resources guarded by the semaphore and returns true on success. If available() < n , this call immediately returns false without acquiring any resources.

范例：

sem = QSemaphore(5)      # sem.available() == 5
sem.tryAcquire(250)      # sem.available() == 5, returns false
sem.tryAcquire(3)        # sem.available() == 2, returns true
											

另请参阅

acquire()

PySide2.QtCore.QSemaphore. tryAcquire ( n , timeout ) ¶

参数

• n – int

• timeout – int

返回类型

bool

Tries to acquire n resources guarded by the semaphore and returns true on success. If available() < n , this call will wait for at most timeout milliseconds for resources to become available.

Note: Passing a negative number as the timeout is equivalent to calling acquire() , i.e. this function will wait forever for resources to become available if timeout is negative.

范例：

sem = QSemaphore(5)             # sem.available() == 5
sem.tryAcquire(250, 1000)       # sem.available() == 5, waits 1000 milliseconds and returns false
sem.tryAcquire(3, 30000)        # sem.available() == 2, returns true without waiting
											

另请参阅

acquire()