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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 handler. In this case it would be terminated, since termination is the
default action for the alarm signals. @xref{Signal Handling}. 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. 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 This facility is declared in the header file @file{sys/time.h}. The
@code{alarm} function, declared in @file{unistd.h}, provides a somewhat @code{alarm} function, declared in @file{unistd.h}, provides a somewhat