POSIX - Hot to check if detached thread is still active


 
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# 8  
Old 09-08-2008
What type of synchronization do you suggest?

I would like to remind you that if thread is terminated due some problem (memory or something like that) synchronization might fail as well.

Also, if I use phtread_join, after thread is terminated, resources will still be occupied until main program is finished.
Since my program is in the endless loop I decide to use detached threads, in order to free resources and make room for new ones.
# 9  
Old 09-08-2008
I'm suggesting that you consider at least something like a shared memory array instead of an internal array, so you have to have a way to communicate. Assuming you need to track what is going on. You can create non-detached threads and still not have to call pthread_join until you know the thread has ended.

Include some timing component in the array - a start time in epoch seconds maybe.
After some ridiculous amount of time has elapsed, like 30 minutes, call pthread_cancel on the offending thread_id. Then open up the slot for reuse.

If threads are dumping core or corrupting memory then this will not fix the problem.
Only code changes can fix that.
# 10  
Old 09-08-2008
The normal threaded way to do what is suggested is to create a monitor thread for notification and use pthread_cond primitives for the synchronization.
Example code follows.
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <time.h>

#define MAXTHREAD 5
#define FIRE 20

typedef struct msg {
pthread_t tnum;
} M;

/*global*/
pthread_cond_t alert = PTHREAD_COND_INITIALIZER;
pthread_mutex_t alertmtx = PTHREAD_MUTEX_INITIALIZER;
static M foo;
void *monitor(void *);
void *do_random(void *);

#define liveloop() {while (1) {sleep(1);}}

int main(void) {
int y = 0;
pthread_t monthread;
pthread_t t[MAXTHREAD];

                       srand(time(NULL));
                       if (pthread_create(&monthread,NULL,monitor,NULL) != 0) {perror("pthread_create()"); return -1;}
                       while (y < MAXTHREAD) {
                                             pthread_create(&t[y],NULL,do_random,NULL);
                                             y++;
                       }
                       liveloop();
}

 void *monitor(void *arg) {

               pthread_mutex_lock(&alertmtx);
               while (1) {
                         pthread_cond_wait(&alert,&alertmtx);
                         printf("Received notification from thread id: %d.\n",foo.tnum);
               }
               pthread_mutex_unlock(&alertmtx);
}
 
void *do_random(void *arg) {
int r;
time_t beg, end;
              pthread_detach(pthread_self());
              r = (int)(1 + rand() % FIRE);       
              end = beg = time(NULL);
              end += r;
              for (;;) {
                  while (end > beg) {
                        beg = time(NULL);
                        sleep(1);
                  }
                  pthread_mutex_lock(&alertmtx);
                  foo.tnum = pthread_self();
                  pthread_cond_signal(&alert);
                  end += r;
                  pthread_mutex_unlock(&alertmtx);
              }
}

Except, instead of liveloop in main(), you'd join on the monitoring thread which would exit the process group in case of calamitous error.

Last edited by ramen_noodle; 09-08-2008 at 05:08 PM..
# 11  
Old 09-09-2008
Quote:
Originally Posted by orangem
What type of synchronization do you suggest?

I would like to remind you that if thread is terminated due some problem (memory or something like that) synchronization might fail as well.

Also, if I use phtread_join, after thread is terminated, resources will still be occupied until main program is finished.
Since my program is in the endless loop I decide to use detached threads, in order to free resources and make room for new ones.
I agree with jim's post. The resources used by each of the created threads can be freed even if the thread is not created as detached. After each thread finishes its task its attribute must be destroyed and pthread_join()'ed to the others to release the resources.
# 12  
Old 09-09-2008
Both ways would work for the op. it seems to me one involves creation of a state machine and the other depends on avoiding serialization blocks imposed by pthread_join.
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