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POEnsuring task execution order in threadpool
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copied!<p>I have been reading about the thread-pool pattern and I can't seem to find the usual solution for the following problem.</p> <p>I sometimes want tasks to be executed serially. For example, I read chunks of text from a file and for some reason I need the chunks to be processed in that order. So basically I want to eliminate concurrency <strong>for some of the tasks</strong>.</p> <p>Consider this scenario where the tasks with <code>*</code> need to be processed in the order they were pushed in. The other tasks can be processed in any order.</p> <pre><code>push task1 push task2 push task3 * push task4 * push task5 push task6 * .... and so on </code></pre> <p>In the context of a thread-pool, without this constraint, a single queue of pending tasks works fine but clearly here it doesn't.</p> <p>I thought about having <em>some of the threads</em> operate on a thread-specific queue and the others on the "global" queue. Then, in order to execute some of the tasks serially, I simply have to push them onto a queue where a single thread looks. It <em>does</em> sounds a bit clumsy.</p> <p>So, the real question in this long story: how would you solve this ? <strong>How would you ensure those tasks are ordered</strong>?</p> <h3>EDIT</h3> <p>As a more general problem, suppose the scenario above becomes</p> <pre><code>push task1 push task2 ** push task3 * push task4 * push task5 push task6 * push task7 ** push task8 * push task9 .... and so on </code></pre> <p>What I mean is that the tasks within a group should be executed sequentially, but the groups themselves can mix. So you can have <code>3-2-5-4-7</code> for example.</p> <p>One other thing to note is that I don't have access to all the tasks in a group upfront (and I can't wait for all of them to arrive before starting the group).</p> <p>Thank you for your time.</p>

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