c - Creating a timeout using time and difftime -

gcc (gcc) 4.6.0 20110419 (red hat 4.6.0-5) 

i trying time of start , end time. , difference between them.

the function have creating api our existing hardware.

the api wait_events take 1 argument time in milli-seconds. trying start before while loop. , using time number of seconds. after 1 iteration of loop time difference , compare difference time out.

many suggestions,

/* wait event specified time out.  * if event occurs before time out return 0  * if event timeouts out before event return -1 */ int wait_events(int timeout_ms) {     time_t start = 0;     time_t end = 0;     double time_diff = 0;     /* convert seconds */     int timeout = timeout_ms / 100;      /* initial time */     start = time(null);     while(true) {         if(open_device_flag == true) {             device_evt.event_id = event_dev_open;             return true;         }         /* end time after each iteration */         end = time(null);         /* difference between times */         time_diff = difftime(start, end);         if(time_diff > timeout) {             /* timed out before getting event */             return false;         }     } } 

the function call this.

int main(void) { #define timeout 500 /* 1/2 sec */     while(true) {         if(wait_events(timeout) != 0) {             /* process incoming event */             printf("event fired\n");         }         else {             printf("event timed out\n");         }     }      return 0; } 

=============== edit updated results ==================

1) no sleep -> 99.7% - 100% cpu 2) setting usleep(10) -> 25% cpu 3) setting usleep(100) -> 13% cpu 3) setting usleep(1000) -> 2.6% cpu 4) setting usleep(10000) -> 0.3 - 0.7% cpu 

you're overcomplicating - simplified:

time_t start = time(); (;;) {     // try     if (time() > start + 5) {         printf("5s timeout!\n");         break;     } } 

time_t should in general int or long int depending on platform counting number of seconds since january 1st 1970.

side note:

int timeout = timeout_ms / 1000; 

one second consists of 1000 milliseconds.

edit - note: you'll have ensure other thread(s) and/or event handling can happen, include kind of thread inactivity (using sleep(), nanosleep() or whatever).