QThreadPool ¶

概要 ¶

详细描述 ¶

QThreadPool manages and recyles individual QThread objects to help reduce thread creation costs in programs that use threads. Each Qt application has one global QThreadPool object, which can be accessed by calling globalInstance() .

To use one of the QThreadPool threads, subclass QRunnable 和实现 run() 虚函数。然后创建该类的对象并把它传递给 start() .

class HelloWorldTask(QRunnable):
    def run(self):
        print "Hello world from thread", QThread.currentThread()
hello = HelloWorldTask()
# QThreadPool takes ownership and deletes 'hello' automatically
QThreadPool.globalInstance().start(hello)
											

QThreadPool deletes the QRunnable 默认情况下是自动的。使用 setAutoDelete() to change the auto-deletion flag.

QThreadPool supports executing the same QRunnable 多次通过调用 tryStart (this) 从 run() . If autoDelete is enabled the QRunnable 将被删除当最后一个线程退出 run 函数时。调用 start() multiple times with the same QRunnable when autoDelete is enabled creates a race condition and is not recommended.

Threads that are unused for a certain amount of time will expire. The default expiry timeout is 30000 milliseconds (30 seconds). This can be changed using setExpiryTimeout() . Setting a negative expiry timeout disables the expiry mechanism.

调用 maxThreadCount() to query the maximum number of threads to be used. If needed, you can change the limit with setMaxThreadCount() 。默认 maxThreadCount() is idealThreadCount() 。 activeThreadCount() function returns the number of threads currently doing work.

reserveThread() function reserves a thread for external use. Use releaseThread() when your are done with the thread, so that it may be reused. Essentially, these functions temporarily increase or reduce the active thread count and are useful when implementing time-consuming operations that are not visible to the QThreadPool .

注意： QThreadPool is a low-level class for managing threads, see the Qt Concurrent module for higher level alternatives.

另请参阅

QRunnable

class QThreadPool ( [ parent=None ] ) ¶

param parent

QObject

构造线程池采用给定 parent .

PySide2.QtCore.QThreadPool. activeThreadCount ( ) ¶

返回类型

int

PySide2.QtCore.QThreadPool. cancel ( runnable ) ¶

参数

runnable – QRunnable

注意

此函数被弃用。

use tryTake() instead, but note the different deletion rules.

移除指定 runnable from the queue if it is not yet started. The runnables for which runnable->autoDelete() 返回 true are deleted.

另请参阅

start() tryTake()

PySide2.QtCore.QThreadPool. clear ( ) ¶

Removes the runnables that are not yet started from the queue. The runnables for which runnable->autoDelete() 返回 true are deleted.

另请参阅

start()

PySide2.QtCore.QThreadPool. expiryTimeout ( ) ¶

返回类型

int

另请参阅

setExpiryTimeout()

static PySide2.QtCore.QThreadPool. globalInstance ( ) ¶

返回类型

QThreadPool

返回全局 QThreadPool 实例。

PySide2.QtCore.QThreadPool. maxThreadCount ( ) ¶

返回类型

int

另请参阅

setMaxThreadCount()

PySide2.QtCore.QThreadPool. releaseThread ( ) ¶

Releases a thread previously reserved by a call to reserveThread() .

注意

Calling this function without previously reserving a thread temporarily increases maxThreadCount() . This is useful when a thread goes to sleep waiting for more work, allowing other threads to continue. Be sure to call reserveThread() when done waiting, so that the thread pool can correctly maintain the activeThreadCount() .

另请参阅

reserveThread()

PySide2.QtCore.QThreadPool. reserveThread ( ) ¶

Reserves one thread, disregarding activeThreadCount() and maxThreadCount() .

Once you are done with the thread, call releaseThread() to allow it to be reused.

注意

This function will always increase the number of active threads. This means that by using this function, it is possible for activeThreadCount() to return a value greater than maxThreadCount() .

另请参阅

releaseThread()

PySide2.QtCore.QThreadPool. setExpiryTimeout ( expiryTimeout ) ¶

参数

expiryTimeout – int

另请参阅

expiryTimeout()

PySide2.QtCore.QThreadPool. setMaxThreadCount ( maxThreadCount ) ¶

参数

maxThreadCount – int

另请参阅

maxThreadCount()

PySide2.QtCore.QThreadPool. setStackSize ( stackSize ) ¶

参数

stackSize – uint

另请参阅

stackSize()

PySide2.QtCore.QThreadPool. stackSize ( ) ¶

返回类型

uint

另请参阅

setStackSize()

PySide2.QtCore.QThreadPool. start ( runnable [ , priority=0 ] ) ¶

参数

• runnable – QRunnable

• priority – int

Reserves a thread and uses it to run runnable , unless this thread will make the current thread count exceed maxThreadCount() . In that case, runnable is added to a run queue instead. The priority argument can be used to control the run queue’s order of execution.

Note that the thread pool takes ownership of the runnable if runnable->autoDelete() 返回 true ，和 runnable will be deleted automatically by the thread pool after the runnable->run() returns. If runnable->autoDelete() 返回 false , ownership of runnable remains with the caller. Note that changing the auto-deletion on runnable after calling this functions results in undefined behavior.

PySide2.QtCore.QThreadPool. tryStart ( runnable ) ¶

参数

runnable – QRunnable

返回类型

bool

Attempts to reserve a thread to run runnable .

If no threads are available at the time of calling, then this function does nothing and returns false 。否则， runnable is run immediately using one available thread and this function returns true .

Note that on success the thread pool takes ownership of the runnable if runnable->autoDelete() 返回 true ，和 runnable will be deleted automatically by the thread pool after the runnable->run() returns. If runnable->autoDelete() 返回 false , ownership of runnable remains with the caller. Note that changing the auto-deletion on runnable after calling this function results in undefined behavior.

PySide2.QtCore.QThreadPool. tryTake ( runnable ) ¶

参数

runnable – QRunnable

返回类型

bool

Attempts to remove the specified runnable from the queue if it is not yet started. If the runnable had not been started, returns true , and ownership of runnable is transferred to the caller (even when runnable->autoDelete() == true ). Otherwise returns false .

注意

若 runnable->autoDelete() == true , this function may remove the wrong runnable. This is known as the ABA problem : the original runnable may already have executed and has since been deleted. The memory is re-used for another runnable, which then gets removed instead of the intended one. For this reason, we recommend calling this function only for runnables that are not auto-deleting.

另请参阅

start() autoDelete()

PySide2.QtCore.QThreadPool. waitForDone ( [ msecs=-1 ] ) ¶

参数

msecs – int

返回类型

bool

Waits up to msecs milliseconds for all threads to exit and removes all threads from the thread pool. Returns true if all threads were removed; otherwise it returns false 。若 msecs is -1 (the default), the timeout is ignored (waits for the last thread to exit).