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| 55 | <H2><A NAME="SECTION009520000000000000000"></A><A NAME="rlock-objects"></A> |
| 56 | <BR> |
| 57 | 7.5.2 RLock Objects |
| 58 | </H2> |
| 59 | |
| 60 | <P> |
| 61 | A reentrant lock is a synchronization primitive that may be |
| 62 | acquired multiple times by the same thread. Internally, it uses |
| 63 | the concepts of ``owning thread'' and ``recursion level'' in |
| 64 | addition to the locked/unlocked state used by primitive locks. In |
| 65 | the locked state, some thread owns the lock; in the unlocked |
| 66 | state, no thread owns it. |
| 67 | |
| 68 | <P> |
| 69 | To lock the lock, a thread calls its <tt class="method">acquire()</tt> method; this |
| 70 | returns once the thread owns the lock. To unlock the lock, a |
| 71 | thread calls its <tt class="method">release()</tt> method. |
| 72 | <tt class="method">acquire()</tt>/<tt class="method">release()</tt> call pairs may be nested; only |
| 73 | the final <tt class="method">release()</tt> (the <tt class="method">release()</tt> of the outermost |
| 74 | pair) resets the lock to unlocked and allows another thread blocked in |
| 75 | <tt class="method">acquire()</tt> to proceed. |
| 76 | |
| 77 | <P> |
| 78 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 79 | <td><nobr><b><tt id='l2h-2722' xml:id='l2h-2722' class="method">acquire</tt></b>(</nobr></td> |
| 80 | <td><var></var><big>[</big><var>blocking<code> = 1</code></var><big>]</big><var></var>)</td></tr></table></dt> |
| 81 | <dd> |
| 82 | Acquire a lock, blocking or non-blocking. |
| 83 | |
| 84 | <P> |
| 85 | When invoked without arguments: if this thread already owns |
| 86 | the lock, increment the recursion level by one, and return |
| 87 | immediately. Otherwise, if another thread owns the lock, |
| 88 | block until the lock is unlocked. Once the lock is unlocked |
| 89 | (not owned by any thread), then grab ownership, set the |
| 90 | recursion level to one, and return. If more than one thread |
| 91 | is blocked waiting until the lock is unlocked, only one at a |
| 92 | time will be able to grab ownership of the lock. There is no |
| 93 | return value in this case. |
| 94 | |
| 95 | <P> |
| 96 | When invoked with the <var>blocking</var> argument set to true, do the |
| 97 | same thing as when called without arguments, and return true. |
| 98 | |
| 99 | <P> |
| 100 | When invoked with the <var>blocking</var> argument set to false, do not |
| 101 | block. If a call without an argument would block, return false |
| 102 | immediately; otherwise, do the same thing as when called |
| 103 | without arguments, and return true. |
| 104 | </dl> |
| 105 | |
| 106 | <P> |
| 107 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 108 | <td><nobr><b><tt id='l2h-2723' xml:id='l2h-2723' class="method">release</tt></b>(</nobr></td> |
| 109 | <td><var></var>)</td></tr></table></dt> |
| 110 | <dd> |
| 111 | Release a lock, decrementing the recursion level. If after the |
| 112 | decrement it is zero, reset the lock to unlocked (not owned by any |
| 113 | thread), and if any other threads are blocked waiting for the lock to |
| 114 | become unlocked, allow exactly one of them to proceed. If after the |
| 115 | decrement the recursion level is still nonzero, the lock remains |
| 116 | locked and owned by the calling thread. |
| 117 | |
| 118 | <P> |
| 119 | Only call this method when the calling thread owns the lock. |
| 120 | Do not call this method when the lock is unlocked. |
| 121 | |
| 122 | <P> |
| 123 | There is no return value. |
| 124 | </dl> |
| 125 | |
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