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On non-Linux POSIX, TriggerFd used a pipe. The qnx_pipes branch uses a Unix domain socketpair instead, which is what QNX and macOS need for the same poll behavior as eventfd.
macOS keeps the pipe. A socketpair was slower there when a publish wakes another thread, and QNX is the platform whose pipe service needs the socketpair.
dallison
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Summary
cpp_toolbeltto10e2b042cb0e4602b8362d50612abf3c8b681ecc(dallison/cpp_toolbelt#32).TriggerFdis a Unix domain socketpair on QNX and a pipe on macOS and other POSIX systems. Linux stays oneventfd.POLLOUTwhile it is open, andco20_rpcwaits on that fd forPOLLIN.On macOS, six opt rounds of
//client:latency_testshowed the socketpair slower when a publish wakes another thread (MultithreadedReliableLatency+11.7%,MultithreadedUnreliableLatency+21.2%) and about the same on a single thread. That is why this pin leaves macOS on the pipe.Test plan
10e2b04and the source keepssocketpairunder__QNX__/__QNXNTO__andpipeotherwise.//toolbelt:triggerfd_testin cpp_toolbelt passed on macOS, which builds the pipe path.