Paul Brook wrote:
I think it still suffers from the same race condition so today it
wouldn't work. You could fix the bottom half scheduling though so that
you could safely schedule a bottom half from a signal handler (using
roughly the same trick).
Fwiw, it's perfectly sensible to have a single pipe which is shared by
all signal handlers, just used to say "check for work flags set".
And if you need the main loop to be able to distinguish signals coming
out of the pipe, then just write the signum into the pipe as a byte,
instead of a single dummy byte. Or even write the whole 'siginfo_t'
struct passed to the signal handler, and read it out in sizeof(siginfo_t)
sized chunks for processing.
I don't think this will works. If the pipe buffer gets full the write will
either block or you'll loose signals.
When using the pipe as a simple semaphore all you care about is the presence
or absence of data. It doesn't matter if subsequent writes loose data (e.g.
by not retrying a nonblocking write) as long as a write to an empty pipe
succeeds.
Yup. You need to use a global flag to distinguish the type of signal.
Regards,
Anthony Liguori
Paul
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