Enabling thread concurrency in Posix Threads.

["Shivakumar Patil" <bond_isct@hotmail.com>]

Hi There,


        I have Potato 2.2.19 kernel and the following packages installed 
libc6-dev 2.2.5-4,
libpth-dev   1.4.1-2 and glibc-doc 2.2.5-4.  I was trying to understand the 
concepts of threads on linux. I executed a program from Stevens book and is 
attached to this mail. On the commandline I passed the following arguments.

               The first argument being the executable , then no of items 
to be processed , no of threads that are used to process these items. 
Following is the output. From the this output , It seems to me that only one 
thread is performing and rest of them are not allowed to run. The 
Set_concurrency() method uses pthread_setconcurrency() internally, so I 
donot where the problem is and I am linking the obj with pthread library.




~/unpv22e/mutex$ ./prodcons1 100 10
In void Set_concurrency(int level)
count[0] = 100
count[1] = 0
count[2] = 0
count[3] = 0
count[4] = 0
count[5] = 0
count[6] = 0
count[7] = 0
count[8] = 0
count[9] = 0

                  Can anybody suggest me where the problem is?









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/* include main */
#include	"unpipc.h"

#define	MAXNITEMS 		1000000
#define	MAXNTHREADS			100

int		nitems;			/* read-only by producer and consumer */
struct {
  pthread_mutex_t	mutex;
  int	buff[MAXNITEMS];
  int	nput;
  int	nval;
} shared = { PTHREAD_MUTEX_INITIALIZER };

void	*produce(void *), *consume(void *);

int
main(int argc, char **argv)
{
	int			i, nthreads, count[MAXNTHREADS];
	pthread_t	tid_produce[MAXNTHREADS], tid_consume;

	if (argc != 3)
		err_quit("usage: prodcons1 <#items> <#threads>");
	nitems = min(atoi(argv[1]), MAXNITEMS);
	nthreads = min(atoi(argv[2]), MAXNTHREADS);

	Set_concurrency(nthreads);
	for (i = 0; i < nthreads; i++) {
		count[i] = 0;
		Pthread_create(&tid_produce[i], NULL, produce, &count[i]);
	}

	for (i = 0; i < nthreads; i++) {
		Pthread_join(tid_produce[i], NULL);
		printf("count[%d] = %d\n", i, count[i]);	
	}

	Pthread_create(&tid_consume, NULL, consume, NULL);
	Pthread_join(tid_consume, NULL);

	exit(0);
}
/* end main */

/* include produce */
void *
produce(void *arg)
{
	for ( ; ; ) {
		if (shared.nput >= nitems) {
			return(NULL);		/* array is full, we're done */
		}
		shared.buff[shared.nput] = shared.nval;
		shared.nput++;
		shared.nval++;
		*((int *) arg) += 1;
	}
}

void *
consume(void *arg)
{
	int		i;

	for (i = 0; i < nitems; i++) {
		if (shared.buff[i] != i)
			printf("buff[%d] = %d\n", i, shared.buff[i]);
	}
	return(NULL);
}
/* end produce */