[Valgrind-users] Scheduler problem

[Sefer T. <se...@ho...>]

Hi!

I've been testing a short threaded program, and I noticed that sleep(x), 
although utilizes no cpu, it schdules poorly (the program slows down almost 
to a halt).

This is a simple threaded queue handler program, which sleeps 2 sec. between 
each update to the queue, however, after 2-3 such updates, the sleep seems 
to triple (or worse) waiting often 10 seconds or more (while being 
completely idle).

This happens to me on Mandrake 9.1 on i686 running valgrind both 1.9.4 and a 
recent snapshot from the CVS.

This might indicate some problem in scheduling blocking commands in general 
(or sleep in particular), after all, why should a sleep(2) wait for 10 
seconds (while the cpu is entirely idle).

If anyone has any ideas or can offer an explanation, I'd appreciate your 
comments.

Thanks,
    Sefer.


####  Makefile
all:
        gcc -g -Wall -D_REENTRANT -o go *.c -lpthread



####  test.c

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



#define MAXT			4
#define MAXD			10



typedef struct
{
	pthread_mutex_t		my_mutex;
	pthread_cond_t		my_cond;
	int			count;
} data_t;




static data_t			gdata[MAXT];




static void data_add(data_t *data)
{
	pthread_mutex_lock(&data->my_mutex);

	while ( data->count >= MAXD ) {
		pthread_cond_wait(&data->my_cond, &data->my_mutex);
	}


	if ( !data->count )
		pthread_cond_signal(&data->my_cond);

	++data->count;

	pthread_mutex_unlock(&data->my_mutex);
}



static void data_remove(data_t *data)
{
	pthread_mutex_lock(&data->my_mutex);

	while ( data->count == 0 ) {
		pthread_cond_wait(&data->my_cond, &data->my_mutex);
	}

	if ( data->count >= MAXD ) pthread_cond_signal(&data->my_cond);
	--data->count;

	pthread_mutex_unlock(&data->my_mutex);
}



static void *thread_proc(void *ptr)
{
	printf("Thread created!\n");

	for ( ; ; ) {
		data_remove((data_t *) ptr);
		printf("Got some data.\n");
	}

	return NULL;
}



static void run()
{
	int i, rc;
	pthread_t tid;

	for ( i = 0; i < MAXT; ++i ) {
		pthread_mutex_init(&gdata[i].my_mutex,  NULL);
		pthread_cond_init(&gdata[i].my_cond, NULL);
		gdata[i].count = 0;

		rc = pthread_create(&tid, NULL, thread_proc, gdata + i);
	}

	for ( ; ; ) {
		data_add(gdata + 0);
		data_add(gdata + 1);
		sleep(2);
	}
}



int main()
{
	run();
	return 0;
}

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