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Example 3 - Thread Argument Passing (Incorrect)
This example performs argument passing incorrectly. It passes the address of variable t, which is shared memory space and visible to all threads. As the loop iterates, the value of this memory location changes, possibly before the created threads can access it.

int rc;
long t;

for(t=0; t<NUM_THREADS; t++) 
{
   printf("Creating thread %ld\n", t);
   rc = pthread_create(&threads[t], NULL, PrintHello, (void *) &t);
   ...
}

Creating thread 0
Creating thread 1
...
Creating thread 7
Hello from thread 140737488348392
Hello from thread 140737488348392
...
Hello from thread 140737488348392
Hello from thread 140737488348392

void *PrintHello(void *threadid) {
    long * tid;
    tid = (long *)threadid;
    printf("Hello World! It's me, thread #%ld!\n", *tid);
    pthread_exit(NULL);
}

int main() {
    pthread_t threads[NUM_THREADS];
    int rc;
    long t;
    for (t = 0; t < NUM_THREADS; t++)
    {
        printf("In main: creating thread %ld\n", t);
        /* Don't try to access memory location of t! 
         * It constantly changes as the loop goes! 
         * Possibly before the created threads can access it
         */
        rc = pthread_create(&threads[t], NULL, PrintHello, (void *) &t);
        if (rc)
        {
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }
    }

    /* Last thing that main() should do */
    pthread_exit(NULL);
    return 0;
}

In main: creating thread 0
In main: creating thread 1
Hello World! It's me, thread #1!
In main: creating thread 2
Hello World! It's me, thread #2!
In main: creating thread 3
Hello World! It's me, thread #3!
In main: creating thread 4
Hello World! It's me, thread #4!
Hello World! It's me, thread #5!