Open System Services Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

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alarm(3) OSS Library Calls Reference Manual

NAME

alarm - Sets or changes the timeout value for interval timers

LIBRARY

G-series native Guardian processes: system library

G-series native OSS processes: system library

H-series and J-series native Guardian processes: implicit libraries

H-series and J-series OSS processes: implicit libraries

32-bit H-series and J-series OSS processes that use the POSIX User Thread Model library: |

/G/system/zdllnnn/zputdll

64-bit H-series and J-series OSS processes that use the POSIX User Thread Model library: |

/G/system/zdllnnn/yputdll

SYNOPSIS

#include <unistd.h>

unsigned int alarm(

unsigned int seconds);

PARAMETERS

seconds Speciﬁes the number of real-time seconds before the timer expires. Any value

greater than the system maximum of 0x7FFFFFFF one-hundredths of a second

is reduced to the system maximum without informing the caller.

DESCRIPTION

The alarm( ) function is used to obtain notiﬁcation of a timeout after the number of real-time

seconds speciﬁed by the seconds parameter have elapsed.

When the number of seconds speciﬁed by the seconds parameter have elapsed, a SIGALRM sig-

nal is sent to the process. The receipt of this signal might be delayed because of scheduling

conﬂicts.

Each call to alarm( ) overrides any previous setting. Calling alarm( ) with the value 0 (zero) in

the seconds parameter cancels the timer.

Use From a Threaded Application

The thread-aware alarm( ) function instructs the alarm clock of the calling thread to send a

SIGALRM signal to the process after the number of real-time seconds speciﬁed by the seconds

parameter have elapsed. If the value of seconds parameter is 0 (zero), any previously set alarm is

cancelled and no new alarm is scheduled. Each call to the alarm( ) function from a thread super-

cedes any previous calls from the same thread. If the same thread calls the alarm( ) function

multiple times, the value of the seconds parameter from the most recent call is used.

The thread-aware behavior for this function is always enabled in the POSIX User Thread (PUT)

library.

Use From the Guardian Environment

The actions of this function are undeﬁned if it is called from a TNS or accelerated Guardian pro-

cess or from any privileged process.

NOTES

To use the alarm( ) functionality in a threaded application that uses the Standard POSIX Threads

library, see spt_alarm(2).

To use this function in a threaded application that uses the POSIX User Thread Model library on

systems running H06.21 or later RVUs or J06.10 or later RVUs, you must perform all of the fol-

lowing tasks to make the function thread-aware in a multi-threaded application:

• Compile the application using the _PUT_MODEL_ feature test macro or equivalent

compiler command option.

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