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<h1 class="topictitle1">Task Scheduler Summary</h1>
<div><p>The task scheduler works most efficiently for fork-join parallelism with lots of forks, so that the task-stealing can cause sufficient breadth-first behavior to occupy threads, which then conduct themselves in a depth-first manner until they need to steal more work. </p>
<p>The task scheduler is not the simplest possible scheduler because it is designed for speed. If you need to use it directly, it may be best to hide it behind a higher-level interface, as the templates <samp class="codeph">parallel_for</samp>, <samp class="codeph">parallel_reduce</samp>, etc. do. Some of the details to remember are:</p>
<ul type="disc"><li><p>Always use <samp class="codeph">new(<var>allocation_method</var>) <var>T</var></samp> to allocate a <samp class="codeph">task</samp>, where <em>allocation_method</em> is one of the allocation methods of class <samp class="codeph">task</samp>. Do not create local or file-scope instances of a <samp class="codeph">task</samp>.</p>
</li>
<li><p>All siblings should be allocated before any start running, unless you are using <samp class="codeph">allocate_additional_child_of</samp>.</p>
</li>
<li><p>Exploit continuation passing, scheduler bypass, and task recycling to squeeze out maximum performance.</p>
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<li><p>If a task completes, and was not marked for re-execution, it is automatically destroyed. Also, its successor’s reference count is decremented, and if it hits zero, the successor is automatically spawned. </p>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="../tbb_userguide/The_Task_Scheduler.htm">The Task Scheduler</a></div>
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