race condition during termination process
- From: "briggs" <dae.keun.lee@xxxxxxxxx>
- Date: 10 Mar 2006 05:33:18 -0800
Have you ever heard about lupg's multithread tutorials?
This is the tutorial's URL:
http://users.actcom.co.il/~choo/lupg/tutorials/multi-thread/multi-thread.html
There are 2 exercise at the last part of chapter 7.7(Threads
Cancellation - A Complete Example) of that tutorial.
The first exercise is:
Exercise: Our Last Program contains some possible race condition during
its termination process. Can you see what this race is all about? Can
you offer a complete solution to this problem? (hint - think of what
happens to threads deleted using 'delete_handler_thread()').
But I couldn't find the cause of race condition and the solution.
Following program is basically almost same as "Their Last Program":
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#define LOOP_COUNT 600
pthread_mutex_t lock = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
pthread_cond_t radio = PTHREAD_COND_INITIALIZER;
int request_finished = 0;
/* The count of requests that worker thread handled. */
int request_index;
/* The count of requests that main thread made. */
int request_count;
void
cleanup_thr(void *arg)
{
pthread_mutex_unlock(&lock);
}
void*
construct_thr(void *arg)
{
pthread_cleanup_push(cleanup_thr, arg);
pthread_mutex_lock(&lock);
while (1) {
/* If there is any request not yet handled, */
if (request_index < request_count) {
request_index++;
}
else {
/* If there are no more newly created requests */
if (request_finished) {
pthread_mutex_unlock(&lock);
pthread_exit(NULL);
}
else {
pthread_cond_wait(&radio, &lock);
}
}
}
/* Never reached */
pthread_mutex_unlock(&lock);
pthread_cleanup_pop(0);
return (void *) NULL;
}
int
main()
{
int i, j, k;
int thr_id[LOOP_COUNT];
pthread_t thr_pool[LOOP_COUNT];
void *rv;
for (i = 0, j = 0, k = 0; i < LOOP_COUNT; i++) {
/* Make requests as many as LOOP_COUNT */
pthread_mutex_lock(&lock);
request_count++;
pthread_cond_signal(&radio);
pthread_mutex_unlock(&lock);
/* Cancel the oldest thread */
/* Cancellation is done by 2% chance of the time */
if (rand() % 100 < 2) {
if (k < j) {
pthread_cancel(thr_pool[k++]);
}
}
/* Create thread */
/* Creation is done by 5% chance of the time */
if (rand() % 100 < 5) {
thr_id[j] = j;
pthread_create(&thr_pool[j], NULL, construct_thr, (void *)
&thr_id[j]);
j++;
}
}
/* Notify all threads that there are "No More Newly created
Requests" */
pthread_mutex_lock(&lock);
request_finished = 1;
pthread_cond_broadcast(&radio);
pthread_mutex_unlock(&lock);
/* Waiting for each thread exiting */
for (i = k; i < j; i++) {
pthread_join(thr_pool[i], &rv);
/* But, pthread_join() never returns. */
/* Some threads never wake up! */
/* Is this race condition? */
/* Is it related with pthread_cancel() -- as lupg tutorial's hint
said? */
}
return 0;
}
.
- Follow-Ups:
- Re: race condition during termination process
- From: briggs
- Re: race condition during termination process
- Prev by Date: Re: Question about STL containers in multithreaded environment
- Next by Date: Please help with first multi-thread app
- Previous by thread: Re: Multithreading model: can it be selected?
- Next by thread: Re: race condition during termination process
- Index(es):
Relevant Pages
|
