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| <h3 id="why-isnt-pthread_exit-used-to-exit-a-thread">Why isn’t pthread_exit() used to exit a thread?</h3> |
| <p><code>thread_do</code> used to use pthread_exit(). However that resulted in |
| hard times of testing for memory leaks. The reason is that on pthread_exit() |
| not all memory is freed bt pthread (probably for future threads or false |
| belief that the application is terminating). For these reasons a simple return |
| is used.</p> |
| <p>Interestingly using <code>pthread_exit()</code> results in much more memory being allocated.</p> |
| <h3 id="why-do-you-use-sleep-after-calling-thpool_destroy">Why do you use sleep() after calling thpool_destroy()?</h3> |
| <p>This is needed only in the tests. The reason is that if you call thpool_destroy |
| and then exit immediately, maybe the program will exit before all the threads |
| had the time to deallocate. In that way it is impossible to check for memory |
| leaks.</p> |
| <p>In production you don’t have to worry about this since if you call exit, |
| immediately after you destroyed the pool, the threads will be freed |
| anyway by the OS. If you either way destroy the pool in the middle of your |
| program it doesn’t matter again since the program will not exit immediately |
| and thus threads will have more than enough time to terminate.</p> |
| <h3 id="why-does-wait-use-all-my-cpu">Why does wait() use all my CPU?</h3> |
| <p>Normally <code>wait()</code> will spike CPU usage to full when called. This is normal as long as it doesn’t last for more than 1 second. The reason this happens is that <code>wait()</code> goes through various phases of polling (what is called smart polling).</p> |
| <ul> |
| <li>Initially there is no interval between polling and hence the 100% use of your CPU.</li> |
| <li>After that the polling interval grows exponentially.</li> |
| <li>Finally after x seconds, if there is still work, polling falls back to a very big interval.</li> |
| </ul> |
| <p>The reason <code>wait()</code> works in this way, is that the function is mostly used when someone wants to wait for some calculation to finish. So if the calculation is assumed to take a long time then we don’t want to poll too often. Still we want to poll fast in case the calculation is a simple one. To solve these two problems, this seemingly awkward behaviour is present.</p> |
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