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# 8.9. `mutex` — Mutual exclusion support

2.6 版後已棄用: The `mutex` module has been removed in Python 3.

The `mutex` module defines a class that allows mutual-exclusion via acquiring and releasing locks. It does not require (or imply) `threading` or multi-tasking, though it could be useful for those purposes.

The `mutex` module defines the following class:

class `mutex.``mutex`

  Create a new (unlocked) mutex.

  A mutex has two pieces of state — a 「locked」 bit and a queue. When the mutex is not locked, the queue is empty. Otherwise, the queue contains zero or more `(function, argument)` pairs representing functions (or methods) waiting to acquire the lock. When the mutex is unlocked while the queue is not empty, the first queue entry is removed and its `function(argument)` pair called, implying it now has the lock.

  Of course, no multi-threading is implied – hence the funny interface for `lock()`, where a function is called once the lock is acquired.

## 8.9.1. Mutex Objects

`mutex` objects have following methods:

`mutex.``test`()

  Check whether the mutex is locked.

`mutex.``testandset`()

  「Atomic」 test-and-set, grab the lock if it is not set, and return `True`, otherwise, return `False`.

`mutex.``lock`(function, argument)

  Execute `function(argument)`, unless the mutex is locked. In the case it is locked, place the function and argument on the queue. See `unlock()` for explanation of when `function(argument)` is executed in that case.

`mutex.``unlock`()

  Unlock the mutex if queue is empty, otherwise execute the first element in the queue.