std::sig_atomic_t
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  <csignal>
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|   typedef /* unspecified */ sig_atomic_t;  | 
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An integer type which can be accessed as an atomic entity even in the presence of asynchronous interrupts made by signals.
Notes
Until C++11, which introduced std::atomic and std::atomic_signal_fence, about the only thing a strictly conforming program could do in a signal handler was to assign a value to a volatile static std::sig_atomic_t variable and promptly return.
See also
|    sets a signal handler for particular signal   (function)  | |
|    (C++11)  | 
   fence between a thread and a signal handler executed in the same thread   (function)  |