Actually, thinking about this a bit more, that might not even be
necessary. Is SIGPIPE-via-(read|write) synchronous or asynchronous?
(I.e., is the SIGPIPE guaranteed to arrive during the offending system
call?) I was thinking not, but maybe yes. I can't seem to find a
straight answer. A lot of documents seem to confuse thread-directed and
synchronous, when they're not quite the same thing. SIGALRM-via-alarm()
is thread-directed but obviously asynchronous.
SIGPIPE is a sychronous signal that is called during the read() in libpq. I am not sure what thread-directed is.
Ahh, then the usage in libpq is safe; sorry for the false alarm. The concerns about signal safety are really only for async signals, as the behavior is undefined only when one async signal-unsafe function is called from a signal interrupting another:
"In the presence of signals, all functions defined by this volume of IEEE Std 1003.1-2001 shall behave as defined when called from or interrupted by a signal-catching function, with a single exception: when a signal interrupts an unsafe function and the signal-catching function calls an unsafe function, the behavior is undefined."
thread-directed, by the way, simply means that the signal is directed at a specific thread, not just some thread in the process that doesn't have it masked. It's the difference between kill() and pthread_kill(). AFAIK, all synchronous signals are thread-directed, but not all thread-directed signals are synchronous.
Here the signal is synchronous, so the signal is guaranteed to happen at a safe point (during the read()), so there's no problem.
Thanks, Scott Lamb
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