pthread_cond_timedwait call is not working with mutex locking mechanism - c

Question

I have a logging application. In which after specific time (user configureable time) i need to close the current log file and and create a new log file and log the data.
There are 2 critical sections of code in my program.
Writing the data to file (in while(1))
Close and open the new file
Whenever time expires i need to stop the logging to the file and close it & open the new log file and start logging.
For this purpose i have created a sample application exactly same as my application, but instead of file operation here am doing with printf.
I am using pthread_cond_timedwait call to handle the timer related operation. Here is my sample code -
#include <stdio.h>
#include <sys/time.h>
#include <errno.h>
#include <pthread.h>
/* For safe condition variable usage, must use a boolean predicate and */
/* a mutex with the condition. */
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
#define WAIT_TIME_SECONDS 10
void *threadfunc(void *parm)
{
int rc;
struct timespec abstime;
struct timeval now;
/* Usually worker threads will loop on these operations */
while (1) {
rc = gettimeofday(&now, NULL);
/* Convert from timeval to timespec */
abstime.tv_sec = now.tv_sec + WAIT_TIME_SECONDS;
abstime.tv_nsec = (now.tv_usec + 1000UL * WAIT_TIME_SECONDS) * 1000UL;
abstime.tv_sec += abstime.tv_nsec / (1000 * 1000 * 1000);
abstime.tv_nsec %= (1000 * 1000 * 1000);
printf("Thread blocked\n");
pthread_mutex_lock(&mutex);
rc = pthread_cond_timedwait(&cond, &mutex, &abstime);
pthread_mutex_unlock(&mutex);
printf("Wait timed out!\n");
/* critical section of code */
pthread_mutex_lock(&lock);
printf("Thread consumes work here\n");
pthread_mutex_unlock(&lock);
}
return NULL;
}
int main(int argc, char **argv)
{
int rc=0;
pthread_t threadid;
rc = pthread_create(&threadid, NULL, threadfunc, NULL);
if (rc != 0) {
printf("Thread creation failed err:%d\n", errno);
return -1;
}
while (1) {
/* critical section of code */
sleep(1);
pthread_mutex_lock(&lock);
printf("One work item to give to a thread\n");
pthread_mutex_unlock(&lock);
}
printf("Wait for threads and cleanup\n");
pthread_join(threadid, NULL);
pthread_cond_destroy(&cond);
pthread_mutex_destroy(&mutex);
printf("Main completed\n");
return 0;
}
This code is not working. Whenever pthread_cond_timedwait expires threadfunc function should acquire mutex lock and it needs print the statements. After printing am releasing the mutex. But it is not happening. Control is never transfered from main() to threadfunc. Whats is going wrong here?
But instead of mutex if i use a variable to do the handling of critical section of code am able to do it. Say -
static int stop = 0; // take a global variable
//inside threadfunc
/* critical section of code */
stop = 1; //Replace pthread_mutex_lock with this
printf("Thread consumes work here\n");
stop = 0; //Replace pthread_mutex_unlock with this
//in main()
while (1) {
/* critical section of code */
sleep(1);
if (!stop)
printf("One work item to give to a thread\n");
}
This approach is working fine.
When i am using more then one mutex in my code am not able to implement this. What is the real thing happening behind? Am i missing anything while am using mutex to handle critical section of a code?
Thanks in advance!