multithreaded task-queue

gistfile1.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

struct queue_obj { struct queue_obj *next; void *obj_to_free; };

struct queue_obj* firstElement;
struct queue_obj* lastElement;

long goal;

void *consumer(void *arg) {
    long freed = 0;
    while (freed < goal) {
        if (firstElement->obj_to_free != NULL) {
            freed++;
        }
        free(firstElement->obj_to_free);
        firstElement->obj_to_free = NULL;
        if (firstElement->next) {
            struct queue_obj* oldFirstElement = firstElement;
            firstElement = firstElement->next;
            free(oldFirstElement);
        } else {
            usleep(5000);
        }
    }
    free(firstElement);
    return NULL;
}

// produce must always be called from the same thread
void produce(void *obj_to_free) {
    struct queue_obj* new_obj = malloc(sizeof(*new_obj));
    new_obj->next = NULL;
    new_obj->obj_to_free = obj_to_free;
    lastElement->next = new_obj;
    lastElement = new_obj;
}

int main(int argc, char *argv[]) {
    goal = strtol(argv[1], NULL, 10);

    pthread_t thread;
    pthread_create(&thread, NULL, consumer, NULL);

    firstElement = lastElement = malloc(sizeof(*firstElement));
    firstElement->next = NULL;
    firstElement->obj_to_free = NULL;

    long i;
    void *garbage;
    for (i = 0; i < goal; i++) {
        garbage = malloc(1);
        produce(garbage);
    }

    pthread_join(thread, NULL);
    return 0;
}

// $ cc main.c -o main && valgrind --leak-check=full --show-reachable=yes ./main 10000
// ==7359== Memcheck, a memory error detector
// ==7359== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
// ==7359== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
// ==7359== Command: ./main 10000
// ==7359==
// --7359-- run: /usr/bin/dsymutil "./main"
// warning: no debug symbols in executable (-arch x86_64)
// ==7359==
// ==7359== HEAP SUMMARY:
// ==7359==     in use at exit: 25,602 bytes in 373 blocks
// ==7359==   total heap usage: 20,450 allocs, 20,077 frees, 201,562 bytes allocated
// ==7359==
// ==7359== LEAK SUMMARY:
// ==7359==    definitely lost: 0 bytes in 0 blocks
// ==7359==    indirectly lost: 0 bytes in 0 blocks
// ==7359==      possibly lost: 0 bytes in 0 blocks
// ==7359==    still reachable: 0 bytes in 0 blocks
// ==7359==         suppressed: 25,602 bytes in 373 blocks
// ==7359==
// ==7359== For counts of detected and suppressed errors, rerun with: -v
// ==7359== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 15 from 15)