Usage sample of unix signal to handle function call with a timeout value.

Suppose a function "fun" can be blocked, and the its caller hope it will be returned back if "fun" is running too much long; in other words, "fun()" can be overwritten with "fun(int timeout)"

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <time.h>

#include <assert.h>

#include <signal.h>

#include <setjmp.h>

sigjmp_buf run_with_timeout_env;

void

abort_run_with_timeout (int sig)

{

assert (sig == SIGALRM);

siglongjmp (run_with_timeout_env, -1);

}

void fun(int secs)

{

printf("[%d] sleep %d seconds, start.../n",time(NULL), secs);

sleep(secs);

printf("[%d] sleep %d seconds, end/n",time(NULL), secs);

}

int main(int argc, char* argv[])

{

signal (SIGALRM, abort_run_with_timeout);

if (sigsetjmp(run_with_timeout_env,1) != 0)

{

printf("[%d] here longjmp returned./n",time(NULL)); // "fun()" will be return in 2 seconds, so it must come here.

signal (SIGALRM, SIG_DFL);

return 1;

}

printf("[%d] start a 2 seconds alarm./n",time(NULL));

alarm (2); // a alarm signal will be invoked within 2 seconds.

printf("[%d] start calling user funcation./n",time(NULL));

fun(5); // this require the function "fun" will return in 5 seconds, as we know there is a 2-seconds alarm signl

printf("[%d] clear alarm./n",time(NULL));

alarm (0);

printf("[%d] restore signal function back./n",time(NULL));

signal (SIGALRM, SIG_DFL);

}

The program is compiled under Solaris 5.10, Sun Studio 11

#:cc alarm.c

#:./a.out

[1263108032] start a 2 seconds alarm.

[1263108032] start calling user funcation.

[1263108032] sleep 5 seconds, start...

[1263108034] here longjmp returned.