CODEWITHSUNDEEP
cpthreads
oomkiller
oomkiller

Reputation: 179

Pthread passing arguments

char buff[MAX_SIZE];

int main() {

    pthread_t thread[3];

    char message1 = 17;  //17 = 0x11
    char message2 = 18;
    char message3 = 19;
    char message4 = 20;

    int iret[3];
    int k;

    char message[] = {17, 18,19,20};

    /*THIS IS WORKING  

    iret[0] = pthread_create( &thread[0], NULL, write_to_buffer, (void*) &message1);
    iret[1] = pthread_create( &thread[1], NULL, write_to_buffer, (void*) &message2);
    iret[2] = pthread_create( &thread[2], NULL, write_to_buffer, (void*) &message3);
    iret[3] = pthread_create( &thread[3], NULL, write_to_buffer, (void*) &message4);
    */


    /* BUT THIS IS NOT 

    iret[0] = pthread_create( &thread[0], NULL, write_to_buffer, (void*) message);
    iret[1] = pthread_create( &thread[1], NULL, write_to_buffer, (void*) (message+1));
    iret[2] = pthread_create( &thread[2], NULL, write_to_buffer, (void*) (message+2));
    iret[3] = pthread_create( &thread[3], NULL, write_to_buffer, (void*) (message+3));

    */

    for(k=0;k<=3;k++)   {
        pthread_join( thread[k], NULL);
    }


    //rest of main

}


void *write_to_buffer( void *ptr ) {

    while(1)    {
        pthread_mutex_lock(&my_mutex);


        char *message;
        message = (char *) ptr;

        //when passing by array I'm unable to get the value in the message variable

        printf("\nMeeee = %#x  ", *(char*)ptr);



        //REST OF THE FUNCTION //logic to write to buffer

        pthread_mutex_unlock(&my_mutex);

        //SOME LOGIC I OMMITED HERE
        //to return if(indexx >= MAX_SIZE) return(NULL);        
    }   
}

the problem i'm facing is that when i'm passing the array element i'm unable to capture the value in the thread function. but when i'm passing address of message1, message2, message3, and message4 i'm able to get the value passed in thread function

Upvotes: 0

Views: 1392

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409176

You have a couple of cases of undefined behavior in your code. You declare the thread and iret arrays of size three, but create four threads thereby overwriting beyond the bounds of these arrays. This might affect the result of your program and its output, as it might cause the data you pass to be overwritten.

Upvotes: 1

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