ConnectBG handles asynchronous connects by spinning up a background thread to call ::connect(). We kick that thread out of connect, after a timeout, by calling close. This isn't safe because:
Thread A: Your call to Socket::connect()
Thread B: BG connector for A
Thread C: Unrelated thread calling Socket::connect()
Thread D: BG connector for C
Thread A Thread B Thread C Thread D
Start Thread B
connect(N)
Wait 4.9999 seconds
get EINTR
Trigger timeout
shutdown(N)
close(N)
N = socket()
connect(N)
connect(N)
errno == EISCONN
Which can lead us to connect a fd to the wrong endpoint.
We can work around this by only calling shutdown from the parent thread, waiting for the child to join, then calling close.
- is duplicated by
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SERVER-13375 don't rely on ConnectBG thread for nonblocking connect
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- Closed
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- is related to
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SERVER-27358 Socket::connect expects _timeout field to be in milliseconds
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- Closed
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