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<H3><A NAME="SECTION009541000000000000000"></A><A NAME="semaphore-examples"></A>
<BR>
7.5.4.1 <tt class="class">Semaphore</tt> Example 
</H3>

<P>
Semaphores are often used to guard resources with limited capacity, for
example, a database server.  In any situation where the size of the resource
size is fixed, you should use a bounded semaphore.  Before spawning any
worker threads, your main thread would initialize the semaphore:

<P>
<div class="verbatim"><pre>
maxconnections = 5
...
pool_sema = BoundedSemaphore(value=maxconnections)
</pre></div>

<P>
Once spawned, worker threads call the semaphore's acquire and release
methods when they need to connect to the server:

<P>
<div class="verbatim"><pre>
pool_sema.acquire()
conn = connectdb()
... use connection ...
conn.close()
pool_sema.release()
</pre></div>

<P>
The use of a bounded semaphore reduces the chance that a programming error
which causes the semaphore to be released more than it's acquired will go
undetected.

<P>

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	54	<H3><A NAME="SECTION009541000000000000000"></A><A NAME="semaphore-examples"></A>
	55	<BR>
	56	7.5.4.1 <tt class="class">Semaphore</tt> Example
	57	</H3>
	58
	59	<P>
	60	Semaphores are often used to guard resources with limited capacity, for
	61	example, a database server. In any situation where the size of the resource
	62	size is fixed, you should use a bounded semaphore. Before spawning any
	63	worker threads, your main thread would initialize the semaphore:
	64
65	<P>
66	<div class="verbatim"><pre>
67	maxconnections = 5
68	...
69	pool_sema = BoundedSemaphore(value=maxconnections)
70	</pre></div>
71
72	<P>
73	Once spawned, worker threads call the semaphore's acquire and release
74	methods when they need to connect to the server:
75
76	<P>
77	<div class="verbatim"><pre>
78	pool_sema.acquire()
79	conn = connectdb()
80	... use connection ...
81	conn.close()
82	pool_sema.release()
83	</pre></div>
84
85	<P>
86	The use of a bounded semaphore reduces the chance that a programming error
87	which causes the semaphore to be released more than it's acquired will go
88	undetected.
89
90	<P>
91
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