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Conor MacNeill  committed a49a033

Description of parallel task

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File docs/manual/CoreTasks/parallel.html

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+<meta http-equiv="Content-Language" content="en-us">
+<title>Ant User Manual</title>
+<p>Parallel is a container task - it can contain other Ant tasks. Each nested
+task within the parallel task will be executed in its own thread. </p>
+<p>Parallel tasks have a number of uses in an Ant build file including:
+<li>Taking advantage of available processing resources to reduce build time</li>
+<li>Testing servers, where the server can be run in one thread and the test
+harness is run in another thread.</li>
+<p>Care must be taken when using multithreading to ensure the tasks within the
+threads do not interact. For example, two javac compile tasks which write 
+classes into the same destination directory may interact where one tries to
+read a class for depenency information while the other task is writing the 
+class file. Be sure to avoid these types of interactions within a 
+&lt;parallel&gt; task</p>
+<p>The parallel task has no attributes and does not support any nested 
+elements apart from Ant tasks. Any valid Ant task may be embedded within a 
+parallel task, including other parallel tasks.</p>
+<p>Note that while the tasks within the parallel task are being run, the main 
+thread will be blocked waiting for all the child threads to complete.</p>  
+<p>If any of the tasks within the &lt;parallel&gt; task fails, the remaining 
+tasks in other threads will continue to run until all threads have completed. 
+In this sitiuation, the parallel task will also fail.</p>
+  &lt;wlrun ...&gt;
+  &lt;sequential&gt;
+    &lt;sleep seconds=&quot;30&quot;/&gt;
+    &lt;junit ...&gt;
+    &lt;wlstop/&gt;
+  &lt;/sequential&gt;
+<p>This example represents a typical pattern for testing a server application. 
+In one thread the server is started (the wlrun task). The other thread consists 
+of a three tasks which are performed in sequence. The sleep task is used to 
+give the server time to come up. Another task which is capabale of validating 
+that the server is available could be used in place of the sleep task. The 
+test harness is then run. Once the tests are complete, the server is stopped 
+(using wlstop in this example), allowing both threads to complete. The 
+parallel task will also complete at this time and the build will then 
+  &lt;javac ...&gt; &lt;!-- compiler servlet code --&gt;
+  &lt;wljspc ...&gt; &lt;!-- precompile JSPs --&gt;
+<p>This example shows two independent tasks being run to achieve better 
+resource utilization during the build. In this instance, some servlets are being
+compiled in one thead and a set of JSPs is being precompiled in another. As 
+noted above, you need to be careful that the two tasks are independent, both in 
+terms of their dependencies and in terms of their potential interactions in
+Ant's external environment.</p>
+<p align="center">Copyright &copy; 2000,2001 Apache Software Foundation. All rights

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+<a href="CoreTasks/parallel.html">Parallel</a><br>
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