Linux C setitimer Usage instructions __linux

Turn from: http://blog.csdn.net/lixianlin/article/details/25604779

In Linux C programming, Setitimer is a relatively common function, can be used to realize the delay and timing of the function, the Internet has a variety of sporadic usage instructions, have only mentioned the individual usage, today, the practice of sorting out a more detailed:

Header files to be introduced when using:[CPP]View plain copy #include <sys/time.h> setitimer function prototype:[CPP]View plain copy int setitimer (int which, const struct itimerval *new_value, struct itimerval); Where the which parameter represents the type, the optional values are:Itimer_real: In the real time of the system, it sends out the SIGALRM signal.itimer_virtual: The process is calculated by the time it takes in the user state to send a SIGVTALRM signal.itimer_prof: The process in the user state and the kernel state of the time to calculate, it sends out the SIGPROF signal. followed by the New_value and Old_value are itimerval structures, first look at the definition of the ITIMERVAL structure:[CPP]View plain copy struct Itimerval {struct timeval it_interval;/* Next value */struct timeval;      /* Current value */};         struct Timeval {time_t tv_sec;        /* seconds * * suseconds_t tv_usec;   /* microseconds */}; Itimeval is also composed of two timeval structures, Timeval contains tv_sec and tv_usec, where tv_se is seconds and tv_usec is microseconds (i.e. 1/1000000 seconds).

The New_value parameter is used to set the timer, It_interval is the time interval, it_value is the delay length, the following example indicates that after the Setitimer method call succeeds, the delay of 1 microseconds triggers a SIGALRM signal. The SIGALRM signal is triggered once every 200 milliseconds.

SetTimer work mechanism is, first to It_value Countdown, when the it_value for zero trigger signal, and then reset to It_interval, continue to the It_value countdown, has been such a cycle down.

Based on this mechanism, Setitimer can be used both for delay execution and timed execution.

if the It_value is 0 does not trigger the signal, so to be able to trigger the signal, It_value is greater than 0, if the it_interval is zero, will only delay, will not be timed (that is, only one signal will be triggered).

The Old_value parameter, usually not used, is set to NULL, which is used to store the New_value value set when the last Setitimer call was made.

Here is a simple example of use:
[CPP] View plain copy #include  <stdio.h>   #include  <signal.h>   #include   <sys/time.h>      Void signalhandler (int signo)    {       switch  (signo) {           case  SIGALRM:               printf (" caught the sigalrm signal!\n ");                break;      }  }      int  Main (int argc, char *argv[])    {       signal (SIGALRM,  signalhandler);          struct itimerval new_value,  old_value;       new_value.it_value.tv_sec = 0;        new_value.it_value.tv_usec = 1;       new_value.it_interval.tv_ sec = 0;       new_value.it_interval.tv_usec = 200000;        setitimer (Itimer_real, &new_value, &old_value);              for (;;);                return 0;  }