Multithreaded FIFO Gate (Python)

2008-09-08T08:29:14-07:00

Python recipe 576418 by Anand (semaphores, synchronization, system, threading). Revision 5.

While programming with multiple threads, sometimes one needs a construct which allows to suspend the execution of a set of running threads. This is normally required by an outside thread which wants to suspend the running threads for performing a specific action. The threads need to resume after the action in the same order in which they got suspended.

A thread gate (or gateway) allows you to do this. It acts like a gate through which only one thread can pass at a time. By default the gate is open, allowing all threads to "enter" the gate. When a thread calls "close", the gate is closed, blocking any threads which make a further call to "enter", till the gate is re-opened by the owner, whence the threads resume the order in which they got blocked.

The real-life parallel for this is a human operated level cross, which allows only one vehicle to pass at a time.

Synchronizing worker threads using a common input source (Python)

2010-08-09T16:24:38-07:00

Python recipe 577350 by Uri Sternfeld (multithreading, synchronization).

This class is used to synchronize worker threads that get their input from a common source that changes over time, and may even be empty on some occasions.

The problem is that the threads are unaware of the existence of other threads, and have no way of knowing whether any new input will be inserted by other threads. Instead of using a separate 'control' thread, or having the threads exit needlessly each time the input source is empty, a WorkersLounge instance can be used to synchronize them.

The commonest example is using a shared Queue.Queue object, where each thread may put additional jobs into it depending on its current job. When the queue is empty, the other threads 'rest' in the 'lounge'. When the last thread with a job is trying to 'rest', all the threads exit. When a thread puts new jobs into the queue, it should wake up any resting thread by calling the 'back_to_work' method.

Decoupled Proxy of a State Bearing Object in a Multiprocessing Environment (Python)

2010-04-08T04:36:05-07:00

Python recipe 577180 by Mateyuzo (access, multiprocessing, process, processing, subprocess, synchronization, syncmanager, threading, __getattribute__). Revision 2.

Describes a simple example of the potential for shared Singleton or Borg object methods to be proxy'd by an object that SyncManger can present to requesting subprocesses.

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