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POCalling a function when thread is exiting in PThreads or Windows
 

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  1. POCalling a function when thread is exiting in PThreads or Windows
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    <p>I am creating a C++ library for both Linux (with PThreads) and Windows (with their built-in WinThreads) which can be attached to any program, and needs to have a function called when the thread is exiting, similar to how atexit works for processes. </p> <p>I know of pthread_cleanup_push and pthread_cleanup_pop for pthreads, but these do not work for me since they are macros that add another lexical scope, whereas I want to declare this function the first time my library is called into, and then allow the program itself to run its own code however it needs to. I haven't found anything similar in Windows whatsoever. </p> <p>Note that this doesn't mean I want an outside thread to be alerted when the thread stops, or even that I can change the way the thread will be exited, since that is controlled by the program itself, my library is just attached, along for the ride.</p> <p>So the question is: <strong>What is the best way, in this instance, for me to have a function I've written called when the thread closes, in either Windows or Linux, when I have no control over how the thread is created or destroyed?</strong></p> <p>For example in main program:</p> <pre><code>void* threadFunc(void* arg) { printf("Hello world!\n"); return NULL; } int main(int argc, char** argv) { int numThreads = 1; pid_t* pids = NULL; pids = (pid_t*) calloc(sizeof(pid_t), numThreads); pthread_create(&amp;ntid, NULL, threadFunc, &amp;nVal); pthreads[0] = ntid; pthread_join(pthreads[0], NULL); return 0; } </code></pre> <p>In library:</p> <pre><code>void callMeOnExit() { printf("Exiting Thread!\n"); } </code></pre> <p>I would want for callMeOnExit to be called when the thread reaches return NULL; in this case, as well as when the main thread reaches the return 0;. Wrapping pthread_exit would work for other cases, and could be a solution, but I'd like a better one if possible.</p> <p>If anyone has any ideas on how I might be able to do this, that would be great!</p>
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    1. USDave McGinnis
    1. USDave McGinnis
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    1. COYou're creating a C++ library? Well not to be rude, but if you're asking something of this nature instead of reading the relevant specification rigorously then maybe you should just use boost or qt. There are already libraries that do what you want. A one man library is about is realistic as a one man boat crew-that amount of work is impossible if you're going to deliver the features you're talking about. What it sounds like would be applicable is if you wrote a wrapper class this specific work-not a library.
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      1. USAdam Miller
    2. COHowever, for an answer, or perhaps to get a feel of what you are wanting to do: a wrapper class could hide the complexity and manage the creation and starting of the threads and be platform agnostic. I'm sure there's some way that you could make the wrapper class call the function that you want before starting and again/a different function when it exits.
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      1. USAdam Miller
    3. COThe Windows `DLL_THREAD_DETACH` messages sent to a DLL's `Dllmain()` function may help, but I think there are a lot of possible pitfalls as well.
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      1. USMichael Burr
 

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