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(Setting an Alarm): Document that SA_RESTART must not be set when y sycall has to be interrupted.

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Ulrich Drepper 2002-08-26 01:13:25 +00:00
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manual/time.texi
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@ -2301,6 +2301,15 @@ could cause the timer to expire before your program establishes the
handler. In this case it would be terminated, since termination is the
default action for the alarm signals. @xref{Signal Handling}.
To be able to use the alarm function to interrupt a system call which
might block otherwise indefinitely it is important to @emph{not} set the
@code{SA_RESTART} flag when registering the signal handler using
@code{sigaction}. When not using @code{sigaction} things get even
uglier: the @code{signal} function has to fixed semantics with respect
to restarts. The BSD semantics for this function is to set the flag.
Therefore, if @code{sigaction} for whatever reason cannot be used, it is
necessary to use @code{sysv_signal} and not @code{signal}.
The @code{setitimer} function is the primary means for setting an alarm.
This facility is declared in the header file @file{sys/time.h}. The
@code{alarm} function, declared in @file{unistd.h}, provides a somewhat