Merge pull request #363 from bjacob/volatile-disconnect

Make `disconnect` atomic as it's written by a signal handler.
This commit is contained in:
Bartosz Taudul 2022-04-12 21:18:40 +02:00 committed by GitHub
commit 139fad81b9
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@ -4,6 +4,7 @@
# include <unistd.h>
#endif
#include <atomic>
#include <chrono>
#include <inttypes.h>
#include <mutex>
@ -25,11 +26,19 @@
#endif
bool disconnect = false;
// This atomic is written by a signal handler (SigInt). Traditionally that would
// have had to be `volatile sig_atomic_t`, and annoyingly, `bool` was
// technically not allowed there, even though in practice it would work.
// The good thing with C++11 atomics is that we can use atomic<bool> instead
// here and be on the actually supported path.
static std::atomic<bool> s_disconnect { false };
void SigInt( int )
{
disconnect = true;
// Relaxed order is closest to a traditional `volatile` write.
// We don't need stronger ordering since this signal handler doesn't do
// anything else that would need to be ordered relatively to this.
s_disconnect.store(true, std::memory_order_relaxed);
}
[[noreturn]] void Usage()
@ -137,10 +146,15 @@ int main( int argc, char** argv )
const auto t0 = std::chrono::high_resolution_clock::now();
while( worker.IsConnected() )
{
if( disconnect )
// Relaxed order is sufficient here because `s_disconnect` is only ever
// set by this thread or by the SigInt handler, and that handler does
// nothing else than storing `s_disconnect`.
if( s_disconnect.load( std::memory_order_relaxed ) )
{
worker.Disconnect();
disconnect = false;
// Relaxed order is sufficient because only this thread ever reads
// this value.
s_disconnect.store(false, std::memory_order_relaxed );
break;
}
@ -172,7 +186,9 @@ int main( int argc, char** argv )
const auto dur = std::chrono::high_resolution_clock::now() - t0;
if( std::chrono::duration_cast<std::chrono::seconds>(dur).count() >= seconds )
{
disconnect = true;
// Relaxed order is sufficient because only this thread ever reads
// this value.
s_disconnect.store(true, std::memory_order_relaxed );
}
}
}