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POset flag in signal handler
 

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    <p>In C++11, what is the safest (and perferrably most efficient) way to execute unsafe code on a signal being caught, given a type of request-loop (as part of a web request loop)? For example, on catching a SIGUSR1 from a linux command line: <code>kill -30 &lt;process pid&gt;</code></p> <p>It is acceptable for the 'unsafe code' to be run on the next request being fired, and no information is lost if the signal is fired multiple times before the unsafe code is run.</p> <p>For example, my current code is:</p> <pre><code>static bool globalFlag = false; void signalHandler(int sig_num, siginfo_t * info, void * context) { globalFlag = true; } void doUnsafeThings() { // thigns like std::vector push_back, new char[1024], set global vars, etc. } void doRegularThings() { // read filesystem, read global variables, etc. } void main(void) { // set up signal handler (for SIGUSR1) ... struct sigaction sigact; sigact.sa_sigaction = onSyncSignal; sigact.sa_flags = SA_RESTART | SA_SIGINFO; sigaction(SIGUSR1, &amp;sigact, (struct sigaction *)NULL); // main loop ... while(acceptMoreRequests()) { // blocks until new request received if (globalFlag) { globalFlag = false; doUnsafeThings(); } doRegularThings(); } } </code></pre> <p>where I know there could be problems in the main loop testing+setting the globalFlag boolean.</p> <p>Edit: The <code>if (globalFlag)</code> test will be run in a fairly tight loop, and an 'occasional' false negative is acceptable. However, I suspect there's no optimisation over Basile Starynkevitch's solution anyway?</p>
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    1. COI don't think that `c++11` knows about signals. It is an operating system thing (so Posix or Linux).
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      1. USBasile Starynkevitch
    2. CO@BasileStarynkevitch very true. I just tagged this as c++11 in case there are some cleaner workarounds (for managing the flag) specific to c++11. Seems the problem had been solved in POSIX long ago :-)
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    3. COYou should explain what `acceptMoreRequests` does. Where are you calling `poll` (or the nearly obsolete `select`) to multiplex?
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      1. USBasile Starynkevitch
 

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