/********************************************************
* An example source module to accompany...
*
* "Using POSIX Threads: Programming with Pthreads"
* by Brad nichols, Dick Buttlar, Jackie Farrell
* O'Reilly & Associates, Inc.
*
********************************************************
* simple_mutex.c
*
* Simple multi-threaded example with a mutex lock.
* Does the same as the example above (see the link below)
* but with mutual exclusion. Any time a thread starts, it
* request the thread lock. Just one thread is executing
* anytime. The others must wait it to unlock before proceeding.
* quickly comment out by Mij <mij@bitchx.it> for
* http://mij.oltrelinux.com/devel/unixprg/
*
* (also modified a bit on the code itself for clarity and
* expressiveness purposes)
*/
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <pthread.h>
void do_one_thing(int *); /* first thread */
void do_another_thing(int *); /* second thread */
void do_wrap_up(int, int);
int r1 = 0, r2 = 0, r3 = 0;
pthread_mutex_t r3_mutex=PTHREAD_MUTEX_INITIALIZER; /* for mutex locking */
extern int
main(int argc, char **argv)
{
/* thread ids */
pthread_t thread1, thread2;
if (argc > 1)
r3 = atoi(argv[1]);
/* creating the first thread */
if (pthread_create(&thread1,
NULL,
(void *) do_one_thing,
(void *) &r1) != 0)
perror("pthread_create"),exit(1);
/* creating the second thread */
if (pthread_create(&thread2,
NULL,
(void *) do_another_thing,
(void *) &r2) != 0)
perror("pthread_create"),exit(1);
/* expecting the first thread to terminate */
if (pthread_join(thread1, NULL) != 0)
perror("pthread_join"), exit(1);
/* expecting the second thread to terminate */
if (pthread_join(thread2, NULL) != 0)
perror("pthread_join"), exit(1);
do_wrap_up(r1, r2);
return 0;
}
void do_one_thing(int *pnum_times)
{
int i, j, x;
pthread_t ti;
ti = pthread_self(); /* which's our id? */
pthread_mutex_lock(&r3_mutex);
/* this is the segment containing sensitive operations.
* So we need to keep it alone from concurrency for safeness. */
if(r3 > 0) {
x = r3;
r3--;
} else {
x = 1;
}
/* sensitive code end */
pthread_mutex_unlock(&r3_mutex);
for (i = 0; i < 4; i++) {
printf("doing one thing\n");
for (j = 0; j < 10000; j++) x = x + i;
printf("thread %d: got x = %d\n", (int)ti, x);
(*pnum_times)++;
}
}
void do_another_thing(int *pnum_times)
{
int i, j, x;
pthread_t ti;
ti = pthread_self();
pthread_mutex_lock(&r3_mutex);
if(r3 > 0) {
x = r3;
r3--;
} else {
x = 1;
}
pthread_mutex_unlock(&r3_mutex);
for (i = 0; i < 4; i++) {
printf("doing another \n");
for (j = 0; j < 10000; j++) x = x + i;
printf("thread %d: got x = %d\n", (int)ti, x);
(*pnum_times)++;
}
}
void do_wrap_up(int one_times, int another_times)
{
int total;
total = one_times + another_times;
printf("All done, one thing %d, another %d for a total of %d\n",
one_times, another_times, total);
}