I am starting to learn signal handling in Linux and have been trying out some simple codes to deal with SIGALRM. The code shown below sets a timer to count down. When the timer is finished a SIGALRM is produced. The handler for the signal just increments a variable called count. This is repeated until the user hits ‘q’ in the keyboard. The code is shown below:
The problem I am facing is this, when I set the timer for 1000000usec it works fine (i.e 1sec). However if I keep reducing the usec time to 100000, 10000, 1000 etc the timing seems to be too slow. The count variable is not being incremented as fast as it should be. Why is this? I have a hunch I am doing some silly mistake here but I am not sure what it is.
Any help would be greatly appreciated.
Hi,
Just a thought but i might be totally wrong/out of subject: i suspect it has to do with linux timer resolution which is at 10ms (or not?) so no matter how small you set your interval your code will only be ran every 10ms ...
PS.: You query remind me of a "nice surprise" when i was working with timer on linux
HI,
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Hi folks
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Guys,
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Hi guys,
this is my first posting, so at first hi to everyone! ;)
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hi friends i have a problem in signal handling ...
let me explain my problem clearly..
i have four process ..
main process forks two child process and each child process again forks another new process respectively...
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Discussion started by: senvenugopal
2 Replies
LEARN ABOUT BSD
setitimer
GETITIMER(2) System Calls Manual GETITIMER(2)NAME
getitimer, setitimer - get/set value of interval timer
SYNOPSIS
#include <sys/time.h>
#define ITIMER_REAL 0 /* real time intervals */
#define ITIMER_VIRTUAL 1 /* virtual time intervals */
#define ITIMER_PROF 2 /* user and system virtual time */
getitimer(which, value)
int which;
struct itimerval *value;
setitimer(which, value, ovalue)
int which;
struct itimerval *value, *ovalue;
DESCRIPTION
The system provides each process with three interval timers, defined in <sys/time.h>. The getitimer call returns the current value for the
timer specified in which in the structure at value. The setitimer call sets a timer to the specified value (returning the previous value
of the timer if ovalue is nonzero).
A timer value is defined by the itimerval structure:
struct itimerval {
struct timeval it_interval; /* timer interval */
struct timeval it_value; /* current value */
};
If it_value is non-zero, it indicates the time to the next timer expiration. If it_interval is non-zero, it specifies a value to be used
in reloading it_value when the timer expires. Setting it_value to 0 disables a timer. Setting it_interval to 0 causes a timer to be dis-
abled after its next expiration (assuming it_value is non-zero).
Time values smaller than the resolution of the system clock are rounded up to this resolution (on the VAX, 10 milliseconds).
The ITIMER_REAL timer decrements in real time. A SIGALRM signal is delivered when this timer expires.
The ITIMER_VIRTUAL timer decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered
when it expires.
The ITIMER_PROF timer 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 ITIMER_PROF timer expires, the
SIGPROF signal is delivered. Because this signal may interrupt in-progress system calls, programs using this timer must be prepared to
restart interrupted system calls.
NOTES
Three macros for manipulating time values are defined in <sys/time.h>. Timerclear sets a time value to zero, timerisset tests if a time
value is non-zero, and timercmp compares two time values (beware that >= and <= do not work with this macro).
NOTES (PDP-11)
On the PDP-11, setitimer rounds timer values up to seconds resolution. (This saves some space and computation in the overburdened PDP-11
kernel.)
RETURN VALUE
If the calls succeed, a value of 0 is returned. If an error occurs, the value -1 is returned, and a more precise error code is placed in
the global variable errno.
ERRORS
The possible errors are:
[EFAULT] The value parameter specified a bad address.
[EINVAL] A value parameter specified a time was too large to be handled.
SEE ALSO sigvec(2), gettimeofday(2)4.2 Berkeley Distribution August 26, 1985 GETITIMER(2)