thread pool approach

This is a discussion on thread pool approach within the C Programming forums, part of the General Programming Boards category; I have written a demo program below for a thread pool. Do you guys think this is the best approach ...

  1. #1
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    thread pool approach

    I have written a demo program below for a thread pool. Do you guys think this is the best approach for initializing a thread pool, using it to do work, and then cancelling it? I have tested this code and it appears to work. I was just wondering if there is a better approach or if I should change anything.

    Code:
    #define num_workers 5
    pthread_t workers[num_workers];
    pthread_cond_t  available;;		
    pthread_mutex_t lock;
    
    void* doing_stuff();
    
    void cleanup_handler(void *arg) 
    {
      pthread_mutex_unlock(&lock);
    }
    
    int main(int argc, char *argv[])
    {
    	while(1)
    	{
    		pthread_cond_init(&available, NULL);
    	    
    	                if (pthread_mutex_init(&lock, NULL) != 0)
    		{
    			exit(EXIT_FAILURE);
    		}
    		
    		system("clear");
    		
    		printf("\n\n----- Creating threads -----\n\n");
    		int x;
    		for(x =0; x<num_workers; x++)
    		{
    			pthread_create(&workers[x], NULL, doing_stuff, NULL);
    		}
    		
    		sleep(5);
    		
    		printf("\n\n----- Cancelling threads -----\n\n");
    		
    		for(x =0; x<num_workers; x++)
    		{
    			printf("Canceling thread %lu.\n", workers[x]);
    			pthread_cancel(workers[x]);
    		}
    		
    		for(x =0; x<num_workers; x++)
    		{
    			printf("Joining thread %lu.\n", workers[x]);
    			pthread_join(workers[x], NULL);
    		}
    		
    		pthread_mutex_unlock(&lock);
    		pthread_cond_destroy(&available);
    		pthread_mutex_destroy(&lock);
    		
    		sleep(5);
    	}
    	
    	return 0;
    }
    
    void *doing_stuff()
    {
    	printf("Thread %lu has started.\n", pthread_self());
    	pthread_cleanup_push(cleanup_handler, NULL);
    	
    	while(1)
    	{
    		pthread_mutex_lock(&lock);
    		
    		printf("Thread %lu is at wait condition.\n", pthread_self());
    		pthread_cond_wait(&available, &lock); 
    
                                    /* Perform the work */
    		
    		pthread_mutex_unlock(&lock);
    		
    		sleep(5);
    	}
    	pthread_cleanup_pop(0);
    
    	return NULL;
    }

  2. #2
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    Well that's a good start, but it is by no means complete. Now you need to implement the functionality to assign jobs to the thread pool.
    bit∙hub [bit-huhb] n. A source and destination for information.

  3. #3
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    So this is the proper way to cancel threads and wait for them to finish? I know I have to assign jobs still but I have a better understanding of how that will happen. I just wanted to make sure my handler and cancel methodology was correct. Is it ok if I attempt to join each thread when I cancel to ensure that my main routine waits for all threads to finish?

  4. #4
    Registered User Codeplug's Avatar
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    In addition:
    - doing_stuff has the wrong signature
    - main unlocks 'lock' without having locked it
    - don't forget to use a "predicate", associated with the condition, to handle "spurious wakeups" - see the following:
    http://www.opengroup.org/onlinepubs/...#tag_03_515_08
    - cleanup push/pop isn't used correctly - see the following:
    http://www.opengroup.org/onlinepubs/...#tag_03_514_06
    http://www.opengroup.org/onlinepubs/...l#tag_02_09_05
    - and of course, don't skimp on error checking

    gg

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