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:
Code:
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/time.h>
#include <stdlib.h>
void my_action(int);
int count = 0;
int main(int argc, char** argv)
{
struct sigaction sigalrm_action;
struct itimerval timer;
timer.it_interval.tv_sec = 0; //Deal only in usec
timer.it_interval.tv_usec = 1000;
timer.it_value.tv_sec = 0; //Deal only in usec
timer.it_value.tv_usec = 1000;
sigalrm_action.sa_handler = my_action;
sigemptyset(&sigalrm_action.sa_mask);
sigalrm_action.sa_flags = 0;
sigaction(SIGALRM, &sigalrm_action, 0);
printf("Hit any key to start, q to exit\n");
getchar();
if(setitimer(ITIMER_REAL, &timer,NULL) != 0){
perror("Error starting timer");
exit(1);
}
while(getchar()!= 'q');
printf("Bye bye\n");
return 0;
}
void my_action(int signum)
{
count++;
printf("Count is %d\n", count);
}
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,
I need to handle SIGUSR2 signal in my application to change the state of the application dynamically. I have implemented the signal handler. However the application is able to catch only one SIGUSR2 signal. The second SIGUSR2 signal causes the application to crash. This is happning only with... (3 Replies)
Hi folks
I'm trying to write a signal handler (in c on HPUX) that will catch the child process launched by execl when it's finished so that I can check a compliance file.
The signal handler appears to catch the child process terminating however when the signal handler completes the parent... (3 Replies)
Guys,
I'm doing signal handling in Perl. I'm trying to catch ^C signal inside the script.
There two scripts : one shell script and one perl script.
The shell script calls the perl script.
For e.g. shell script a.sh and perl scipt sig.pl.
Shell script a.sh looks something like this :... (6 Replies)
Hi,
I have a main loop which calls a sub loop, which finally returns to the main loop itself. The main loop runs when a flag is set. Now, I have a signal handler for SIGINT, which resets the flag and thus stops the main loop. Suppose I send SIGINT while the program is in subloop, I get an error... (1 Reply)
Hi guys,
this is my first posting, so at first hi to everyone! ;)
I have a problem with ucontext_t in connection with signal handling. I want to simulate a preemptive scheduler. I am using the iTimer with ITIMER_PROF, to schedule the interrupts. You find the code below:
#include <stdio.h>... (18 Replies)
I am trying to write a small program where I can send signals and then ask for an action to be triggered if that signal is received. For example, here is an example where I am trying to write a programme that will say you pressed ctrl*c when someone presses ctrl+c. My questions are what you would... (1 Reply)
i wrote handler for sigsegv such that i can allocate memory for a variable to which
sigsegv generated for illlegal acces of memory.
my code is
#include <signal.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char *j;
void segv_handler(int dummy)
{
j=(char *)malloc(10);
... (4 Replies)
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...
the problem is whenever i kill the child process it is reforking and the... (2 Replies)
Discussion started by: senvenugopal
2 Replies
LEARN ABOUT MOJAVE
setitimer
GETITIMER(2) BSD System Calls Manual GETITIMER(2)NAME
getitimer, setitimer -- get/set value of interval timer
SYNOPSIS
#include <sys/time.h>
#define ITIMER_REAL 0
#define ITIMER_VIRTUAL 1
#define ITIMER_PROF 2
int
getitimer(int which, struct itimerval *value);
int
setitimer(int which, const struct itimerval *restrict value, struct itimerval *restrict 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 non-nil).
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 disabled
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 (typically 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).
RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to
indicate the error.
ERRORS
getitimer() and setitimer() will fail if:
[EFAULT] The value parameter specified a bad address.
[EINVAL] The value parameter specified a time that was too large to be handled or not in the canonical form.
[EINVAL] The which parameter was invalid.
SEE ALSO gettimeofday(2), select(2), sigaction(2)HISTORY
The getitimer() function call appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 4.2 Berkeley Distribution
05-27-2008
