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<html> |
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<head> |
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<meta http-equiv="Content-Language" content="en-us"> |
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<title>Ant User Manual</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: |
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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 depenency 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 sitiuation, the parallel task will also fail.</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 capabale 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 © 2000,2001 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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Conor MacNeill