docs/manual/CoreTasks/parallel.html - ant - Git at Google

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 <h2>Parallel</h2>
 <h3>Description</h3>
 <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:
 <ul>
 <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>
 </ul>

 <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 dependency 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 situation, the parallel task will also fail.</p>

 <p>The parallel task may be combined with the <a href="sequential.html">
 sequential</a> task to define sequences of tasks to be executed on each thread
 within the parallel block</p>

 <h3>Examples</h3>
 <pre>
 &lt;parallel&gt;
   &lt;wlrun ...&gt;
   &lt;sequential&gt;
     &lt;sleep seconds=&quot;30&quot;/&gt;
     &lt;junit ...&gt;
     &lt;wlstop/&gt;
   &lt;/sequential&gt;
 &lt;/parallel&gt;
 </pre>
 <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 capable 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
 continue.</p>

 <pre>
 &lt;parallel&gt;
   &lt;javac ...&gt; &lt;!-- compiler servlet code --&gt;
   &lt;wljspc ...&gt; &lt;!-- precompile JSPs --&gt;
 &lt;/parallel&gt;
 </pre>

 <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>
 <hr>
 <p align="center">Copyright &copy; 2000,2001 Apache Software Foundation. All rights
 Reserved.</p>
 </body>
 </html>
	<html>

	<head>
	<meta http-equiv="Content-Language" content="en-us">
	<title>Ant User Manual</title>
	</head>

	<body>

	<h2>Parallel</h2>
	<h3>Description</h3>
	<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:
	<ul>
	<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>
	</ul>

	<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 dependency information while the other task is writing the
	class file. Be sure to avoid these types of interactions within a
	<parallel> 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 <parallel> task fails, the remaining
	tasks in other threads will continue to run until all threads have completed.
	In this situation, the parallel task will also fail.</p>

	<p>The parallel task may be combined with the <a href="sequential.html">
	sequential</a> task to define sequences of tasks to be executed on each thread
	within the parallel block</p>

	<h3>Examples</h3>
	<pre>
	<parallel>
	<wlrun ...>
	<sequential>
	<sleep seconds="30"/>
	<junit ...>
	<wlstop/>
	</sequential>
	</parallel>
	</pre>
	<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 capable 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
	continue.</p>

	<pre>
	<parallel>
	<javac ...> <!-- compiler servlet code -->
	<wljspc ...> <!-- precompile JSPs -->
	</parallel>
	</pre>

	<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>
	<hr>
	<p align="center">Copyright © 2000,2001 Apache Software Foundation. All rights
	Reserved.</p>
	</body>
	</html>