alarm.3

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)alarm.3	2.1	3/10/87
.TH alarm 3 
.SH Name
alarm \- schedule signal after specified time
.SH Syntax
.nf
.B #include <unistd.h>
.PP
.B unsigned alarm(\fIseconds\fP)
.br
.B unsigned \fIseconds\fP;
.fi
.SH Description
.NXR "alarm subroutine (standard C)"
.NXR "subroutine" "executing at specified time"
.NXA "alarm subroutine (standard C)" "sleep subroutine (standard C)"
The
.PN alarm
subroutine
causes signal SIGALRM, see 
.MS signal 3 ,
to be sent to the invoking process
in a number of seconds given by the argument.
Unless caught or ignored, the signal terminates the process.
.PP
The 
.PN alarm 
requests are not stacked.  Successive calls reset the alarm clock.
If the argument is 0, any 
.PN alarm 
request is canceled.
Because of scheduling delays,
resumption of execution of when the signal is
caught may be delayed an arbitrary amount.
The longest specifiable delay time is 100000000 seconds. Values larger
than 100000000 will be silently rounded down to 100000000.
.PP
The return value is the amount of time
previously remaining in the alarm clock.
.SH Environment
When your program is compiled using the System V environment,
.PN alarm
rounds up any positive fraction of a second to the next second. 
.PP
When your program is compiled using the POSIX environment,
.PN alarm
takes a parameter of type unsigned, and returns a value of type
unsigned.
.SH See Also
getitimer(2), sigpause(2), sigvec(2), signal(3), sleep(3)