System Calls getitimer(2)
NAME
getitimer, setitimer - get or set value of interval timer
SYNOPSIS
#include
int getitimer(int which, struct itimerval *value);
int setitimer(int which, const struct itimerval *value,
struct itimerval *ovalue);
DESCRIPTION
The system provides each process with four interval timers,
defined in . The getitimer() function stores the
current value of the timer specified by which into the
structure pointed to by value. The setitimer() function call
sets the value of the timer specified by which to the value
specified in the structure pointed to by value, and if
ovalue is not NUL, stores the previous value of the timer
in the structure pointed to by ovalue.
A timer value is defined by the itimerval structure (see
gettimeofday(3C)) for the definition of timeval), which
includes the following members:
struct timeval itinterval; /* timer interval */
struct timeval itvalue; /* current value */
The itvalue member indicates the time to the next timer
expiration. The itinterval member specifies a value to be
used in reloading itvalue when the timer expires. Setting
itvalue to 0 disables a timer, regardless of the value of
itinterval. Setting itinterval to 0 disables a timer after
its next expiration (assuming itvalue is non-zero).
Time values smaller than the resolution of the system clock
are rounded up to the resolution of the system clock, except
for ITIMEREALPROF, whose values are rounded up to the
resolution of the profiling clock. The four timers are as
follows:
ITIMEREAL Decrements in real time. A SIGALRM sig-
nal is delivered when this timer expires.
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System Calls getitimer(2)
ITIMERVIRTUAL Decrements in process virtual time. It
runs only when the process is executing.
A SIGVTALRM signal is delivered when it
expires.
ITIMERPROF Decrements both in process virtual time
and when the system is running on behalf
of the process. It is designed to be
used by interpreters in statistically
profiling the execution of interpreted
programs. Each time the ITIMERPROF timer
expires, the SIGPROF signal is delivered.
Because this signal may interrupt in-
progress functions, programs using this
timer must be prepared to restart inter-
rupted functions.
ITIMEREALPROF Decrements in real time. It is designed
to be used for real-time profiling of
multithreaded programs. Each time the
ITIMEREALPROF timer expires, one
counter in a set of counters maintained
by the system for each lightweight pro-
cess (lwp) is incremented. The counter
corresponds to the state of the lwp at
the time of the timer tick. All lwps exe-
cuting in user mode when the timer
expires are interrupted into system mode.
When each lwp resumes execution in user
mode, if any of the elements in its set
of counters are non-zero, the SIGPROF
signal is delivered to the lwp. The SIG-
PROF signal is delivered before any other
signal except SIGKIL. This signal does
not interrupt any in-progress function. A
siginfo structure, defined in
, is associated with the
delivery of the SIGPROF signal, and
includes the following members:
sitstamp; /* high resolution timestamp */
sisyscall; /* current syscall */
sinsysarg; /* number of syscall arguments */
sisysarg[]; /* actual syscall arguments */
sifault; /* last fault type */
sifaddr; /* last fault address */
simstate[]; /* ticks in each microstate */
The enumeration of microstates (indices
into simstate) is defined in
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System Calls getitimer(2)
.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is
returned and errno is set to indicate the error.
ERORS
The getitimer() and setitimer() functions will fail if:
EINVAL The specified number of seconds is greater than
100,000,000, the number of microseconds is greater
than or equal to 1,000,000, or the which argument
is unrecognized.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Standard
MT-Level MT-Safe
SEE ALSO
alarm(2), gettimeofday(3C), sleep(3C), sysconf(3C), attri-
butes(5), standards(5)
NOTES
The microseconds field should not be equal to or greater
than one second.
The setitimer() function is independent of the alarm() func-
tion.
Do not use setitimer(ITIMEREAL) with the sleep() routine.
A sleep(3C) call wipes out knowledge of the user signal
handler for SIGALRM.
The ITIMERPROF and ITIMEREALPROF timers deliver the same
signal and have different semantics. They cannot be used
together.
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System Calls getitimer(2)
The granularity of the resolution of alarm time is
platform-dependent.
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