ThreadPool

class ThreadPool(*args, **kwargs)

The GThreadPool struct represents a thread pool.

A thread pool is useful when you wish to asynchronously fork out the execution of work and continue working in your own thread. If that will happen often, the overhead of starting and destroying a thread each time might be too high. In such cases reusing already started threads seems like a good idea. And it indeed is, but implementing this can be tedious and error-prone.

Therefore GLib provides thread pools for your convenience. An added advantage is, that the threads can be shared between the different subsystems of your program, when they are using GLib.

To create a new thread pool, you use new. It is destroyed by free.

If you want to execute a certain task within a thread pool, use push.

To get the current number of running threads you call get_num_threads. To get the number of still unprocessed tasks you call unprocessed. To control the maximum number of threads for a thread pool, you use get_max_threads. and set_max_threads.

Finally you can control the number of unused threads, that are kept alive by GLib for future use. The current number can be fetched with get_num_unused_threads. The maximum number can be controlled by get_max_unused_threads and set_max_unused_threads. All currently unused threads can be stopped by calling stop_unused_threads.

Methods

class ThreadPool

free(immediate: bool, wait_: bool) → None

Frees all resources allocated for pool.

If immediate is True, no new task is processed for pool. Otherwise pool is not freed before the last task is processed. Note however, that no thread of this pool is interrupted while processing a task. Instead at least all still running threads can finish their tasks before the pool is freed.

If @``wait_`` is True, this function does not return before all tasks to be processed (dependent on immediate, whether all or only the currently running) are ready. Otherwise this function returns immediately.

After calling this function pool must not be used anymore.

Parameters:

immediate – should pool shut down immediately?
wait – should the function wait for all tasks to be finished?

get_max_idle_time() → int

This function will return the maximum interval that a thread will wait in the thread pool for new tasks before being stopped.

If this function returns 0, threads waiting in the thread pool for new work are not stopped.

Added in version 2.10.

get_max_threads() → int: Returns the maximal number of threads for pool.

get_max_unused_threads() → int: Returns the maximal allowed number of unused threads.

get_num_threads() → int: Returns the number of threads currently running in pool.

get_num_unused_threads() → int: Returns the number of currently unused threads.

move_to_front(data: None) → bool

Moves the item to the front of the queue of unprocessed items, so that it will be processed next.

Added in version 2.46.

Parameters:: data – an unprocessed item in the pool

push(data: None) → bool

Inserts data into the list of tasks to be executed by pool.

When the number of currently running threads is lower than the maximal allowed number of threads, a new thread is started (or reused) with the properties given to new(). Otherwise, data stays in the queue until a thread in this pool finishes its previous task and processes data.

error can be None to ignore errors, or non-None to report errors. An error can only occur when a new thread couldn’t be created. In that case data is simply appended to the queue of work to do.

Before version 2.32, this function did not return a success status.

Parameters:: data – a new task for pool

set_max_idle_time(interval: int) → None

This function will set the maximum interval that a thread waiting in the pool for new tasks can be idle for before being stopped. This function is similar to calling stop_unused_threads() on a regular timeout, except this is done on a per thread basis.

By setting interval to 0, idle threads will not be stopped.

The default value is 15000 (15 seconds).

Added in version 2.10.

Parameters:: interval – the maximum interval (in milliseconds) a thread can be idle

set_max_threads(max_threads: int) → bool

Sets the maximal allowed number of threads for pool. A value of -1 means that the maximal number of threads is unlimited. If pool is an exclusive thread pool, setting the maximal number of threads to -1 is not allowed.

Setting max_threads to 0 means stopping all work for pool. It is effectively frozen until max_threads is set to a non-zero value again.

A thread is never terminated while calling func, as supplied by new(). Instead the maximal number of threads only has effect for the allocation of new threads in push(). A new thread is allocated, whenever the number of currently running threads in pool is smaller than the maximal number.

error can be None to ignore errors, or non-None to report errors. An error can only occur when a new thread couldn’t be created.

Before version 2.32, this function did not return a success status.

Parameters:: max_threads – a new maximal number of threads for pool, or -1 for unlimited

set_max_unused_threads(max_threads: int) → None

Sets the maximal number of unused threads to max_threads. If max_threads is -1, no limit is imposed on the number of unused threads.

The default value is 2.

Parameters:: max_threads – maximal number of unused threads

stop_unused_threads() → None: Stops all currently unused threads. This does not change the maximal number of unused threads. This function can be used to regularly stop all unused threads e.g. from timeout_add().

unprocessed() → int: Returns the number of tasks still unprocessed in pool.

Fields

class ThreadPool

exclusive: Are all threads exclusive to this pool

func: The function to execute in the threads of this pool

user_data: The user data for the threads of this pool