C++11 allows the use of atomics in signal handlers, and with the advent of C++ 17 the signal handler feature was again improved. The std::atomic_flag is an atomic boolean type that is guaranteed to be lock-free and can be used in signal handlers. Moreover, the <csignal> header in C++ has an integer type std::sig_atomic_t that can be accessed as an atomic entity even in the presence of asynchronous interrupts made by signals. In this post, we explain how to use atomic_flag in C++.
How to allow atomics use in C++ signal handlers?
The <csignal> header in C++ (or signal.h in C) has an an integer type std::sig_atomic_t that can be accessed as an atomic entity even in the presence of asynchronous interrupts made by signals. In this post, we explain how to allow atomics use in C++ signal handlers.
Here is how we can use it:
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#include <csignal> volatile sig_atomic_t flag = 0; |
Is there a full example of how to use atomics in C++ signal handlers?
Here is an example that has a signal handler and uses sig_atomic_t flag from <csignal>
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#include <iostream> #include <csignal> volatile sig_atomic_t flag = 0; void handler(int signum) { flag = 1 ; } bool signal_check() { if ( signal( SIGINT, handler) == SIG_ERR ) { return false; } if (flag) std::cout << "Flag ON (signal received)\n"; else std::cout << "Flag OFF (signal not received)\n"; return true; } int main(void) { bool b; b = signal_check(); std::cout << "Signal Check:" << b << std::endl; raise (SIGINT); b = signal_check(); std::cout << "Signal Check:" << b << std::endl; system("pause"); return 0; } |
The output will be as follows:
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Flag OFF (signal not received) Signal Check:1 Flag ON (signal received) Signal Check:1 Press any key to continue . . . |
For more information on this feature, see Allow atomics use in signal handlers Proposal document.
If you want to know more about signals and error handlers, I recommend you “CERT C Coding Standard, Second Edition, The: 98 Rules for Developing Safe, Reliable, and Secure Systems”.
https://www.informit.com/store/cert-c-coding-standard-second-edition-98-rules-for-9780321984043
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