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PR: 5020 Reported By: jesse.glick@netbeans.com (Jesse Glick) git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@271131 13f79535-47bb-0310-9956-ffa450edef68
84 lines
3.2 KiB
HTML
84 lines
3.2 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Language" content="en-us">
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<title>Parallel Task</title>
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</head>
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<body>
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<h2>Parallel</h2>
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<h3>Description</h3>
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<p>Parallel is a container task - it can contain other Ant tasks. Each nested
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task within the parallel task will be executed in its own thread. </p>
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<p>Parallel tasks have a number of uses in an Ant build file including:</p>
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<ul>
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<li>Taking advantage of available processing resources to reduce build time</li>
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<li>Testing servers, where the server can be run in one thread and the test
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harness is run in another thread.</li>
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</ul>
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<p>Care must be taken when using multithreading to ensure the tasks within the
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threads do not interact. For example, two javac compile tasks which write
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classes into the same destination directory may interact where one tries to
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read a class for dependency information while the other task is writing the
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class file. Be sure to avoid these types of interactions within a
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<parallel> task</p>
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<p>The parallel task has no attributes and does not support any nested
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elements apart from Ant tasks. Any valid Ant task may be embedded within a
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parallel task, including other parallel tasks.</p>
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<p>Note that while the tasks within the parallel task are being run, the main
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thread will be blocked waiting for all the child threads to complete.</p>
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<p>If any of the tasks within the <parallel> task fails, the remaining
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tasks in other threads will continue to run until all threads have completed.
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In this situation, the parallel task will also fail.</p>
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<p>The parallel task may be combined with the <a href="sequential.html">
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sequential</a> task to define sequences of tasks to be executed on each thread
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within the parallel block</p>
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<h3>Examples</h3>
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<pre>
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<parallel>
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<wlrun ...>
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<sequential>
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<sleep seconds="30"/>
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<junit ...>
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<wlstop/>
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</sequential>
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</parallel>
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</pre>
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<p>This example represents a typical pattern for testing a server application.
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In one thread the server is started (the wlrun task). The other thread consists
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of a three tasks which are performed in sequence. The sleep task is used to
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give the server time to come up. Another task which is capable of validating
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that the server is available could be used in place of the sleep task. The
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test harness is then run. Once the tests are complete, the server is stopped
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(using wlstop in this example), allowing both threads to complete. The
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parallel task will also complete at this time and the build will then
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continue.</p>
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<pre>
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<parallel>
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<javac ...> <!-- compiler servlet code -->
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<wljspc ...> <!-- precompile JSPs -->
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</parallel>
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</pre>
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<p>This example shows two independent tasks being run to achieve better
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resource utilization during the build. In this instance, some servlets are being
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compiled in one thead and a set of JSPs is being precompiled in another. As
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noted above, you need to be careful that the two tasks are independent, both in
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terms of their dependencies and in terms of their potential interactions in
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Ant's external environment.</p>
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<hr>
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<p align="center">Copyright © 2001 Apache Software Foundation. All rights
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Reserved.</p>
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</body>
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</html>
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