To suspend a thread

[meetParantapa]

Is there any function to suspend a thread just like sleep() function. sleep(k) function is invoked inside a process to suspend the current process for 'k' seconds. I want a similar function but for thread level which can be invoked from the thread itself.

#include <pthread.h>
#include <stdio.h>

void  func(void) {
	while (1) {  
		int data = rand()%100;
		printf("Current data is %d ...\n",data);
		
		/* here the thread should be suspended for 3 sec */
	}
}

int main(void) {
    pthread_t thread1;

    srand(time(NULL));

    printf("\n");

    /* Spawn the Thread */
    pthread_create( &thread1, NULL, func, NULL );

    /* to join the thread */
    pthread_join( thread1, NULL );

    printf("\n");

    return 0;
}

[dwks]

sleep() does work on a thread-level basis, just as you want. If one thread is sleeping then another can continue execution.

What are you trying to do, exactly?

[meetParantapa]

Actually, I was implementing a reader's writer's problem, where each reader and writer will be a separate thread. I want the threads to be suspended for a random time. I have tried the sleep(). But it is resulting problems. Threads are supposed to print after reading or writing and this print operation is kept in critical section and hence protected by the semaphore (see the code below). But this printing operation is not executed in proper order.

void *READER(void *arg)
{
	while(1) {
		Lamport_Bakery_read_count(0);	/* waiting for 'read_count' */
		
		read_count++;
		if(read_count == 1)
			Lamport_Bakery_write_access(0);	/* waiting for 'write_access' */

		Exit_for_read_count(0);	/* signal on 'read_count' */

		/* READ OPERATION */
		printf("Reader 1 read %u ... \n",data);
		fflush(stdout);
		        
		Lamport_Bakery_read_count(0);	/* waiting for 'read_count' */

		read_count--;
		if(read_count == 0)
			Exit_for_write_access(0);	/* signal on 'write_access' */

		Exit_for_read_count(0);	/* signal on 'read_count' */
		
		/* threads is to be suspended here */
	}
}

void *WRITER(void *arg)
{
	while (1) {  
		Lamport_Bakery_write_access(3);	/* waiting for 'write_access' */
		
		/* WRITE OPERATION */
		data = rand()%100;
		printf("Writer 3 wrote %d ...\n",data);
		fflush(stdout);
		//sleep(3);
		
		Exit_for_write_access(3);	/* signal on 'write_access' */
		
		usleep(rand()%3000 + 500);
	}
}

[Codeplug]

Assuming that Lamport_Bakery_XXX and Exit_for_XXX are implemented using proper synchronization (via pthread_mutex_t etc.), the biggest issue I see is that multiple READER's can starve all WRITER's due to read_count never reaching 0.

Lamport's bakery algorithm, Dekker's algorithm, Peterson's algorithm, etc - None of these can be implemented in pure C. The assumptions these algorithms make do not hold under modern compilers and hardware.

So if Lamport_Bakery_XXX and Exit_for_XXX don't seem to be providing mutual exclusion, that's probably because they aren't.

gg

[meetParantapa]

Thanks to you all.
I have found the solution. sleep() may be implemented at process level. But for thread level blocking, it may be better to use pthread_cond_timedwait(). Please see this or this for detailed information.

Thank you again for helping.

[Codeplug]

>> sleep() may be implemented at process level.
Wrong.

http://www.opengroup.org/onlinepubs/...ons/sleep.html

If the system if Posix compliant, then it's at the thread level.

gg