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| 55 | <H1><A NAME="SECTION0081300000000000000000"> |
| 56 | 6.13 <tt class="module">mutex</tt> -- |
| 57 | Mutual exclusion support</A> |
| 58 | </H1> |
| 59 | |
| 60 | <P> |
| 61 | <A NAME="module-mutex"></A> |
| 62 | |
| 63 | <P> |
| 64 | The <tt class="module">mutex</tt> module defines a class that allows mutual-exclusion |
| 65 | via acquiring and releasing locks. It does not require (or imply) |
| 66 | threading or multi-tasking, though it could be useful for |
| 67 | those purposes. |
| 68 | |
| 69 | <P> |
| 70 | The <tt class="module">mutex</tt> module defines the following class: |
| 71 | |
| 72 | <P> |
| 73 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 74 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-1988' xml:id='l2h-1988' class="class">mutex</tt></b>(</nobr></td> |
| 75 | <td><var></var>)</td></tr></table></dt> |
| 76 | <dd> |
| 77 | Create a new (unlocked) mutex. |
| 78 | |
| 79 | <P> |
| 80 | A mutex has two pieces of state -- a ``locked'' bit and a queue. |
| 81 | When the mutex is not locked, the queue is empty. |
| 82 | Otherwise, the queue contains zero or more |
| 83 | <code>(<var>function</var>, <var>argument</var>)</code> pairs |
| 84 | representing functions (or methods) waiting to acquire the lock. |
| 85 | When the mutex is unlocked while the queue is not empty, |
| 86 | the first queue entry is removed and its |
| 87 | <code><var>function</var>(<var>argument</var>)</code> pair called, |
| 88 | implying it now has the lock. |
| 89 | |
| 90 | <P> |
| 91 | Of course, no multi-threading is implied - hence the funny interface |
| 92 | for <tt class="method">lock()</tt>, where a function is called once the lock is |
| 93 | acquired. |
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