pthread_join receiving results from function in a array

Question

I'm working with pthreads in C and have run into problems(again). I am trying to send results as an array of a function to my main thread.

This code finds the largest value for each worker(1worker/row) and saves the indexes for that value. So far so good. I will explain my problem below this function. This code does what i want.

for (i = first; i <= last; i++){
    for (j = 0; j < size; j++){
    total += matrix[i][j];
        if(matrix[i][j] > biggest){
    biggest = matrix[i][j]; 
    x=i;
    y=j;
    maxValueResult[1]=i;
    maxValueResult[2]=j;
    }else if(matrix[i][j] < smallest){  
    smallest = matrix[i][j];
            indexes[2]=i;
            indexes[3]=j;   
}
} 
}      
    maxValueResult[0]=biggest;
    maxValueResult[1]=x;
    maxValueResult[2]=y;
printf("Results: maxValue: %d cord[%d,%d]\n",maxValueResult[0],maxValueResult[1],maxValueResult[2]);

return *maxValueResult;

My problem is when i recive the results in pthread_join only maxValueResult[0] works, from maxValueResult[1] and maxValueResult[2] i only get addresses or something. before: " return *maxValueResult;" all three values are correct, looking something like this: "Results: maxValue: 95 cord[3,3]"

Here is where i call pthread_join:

for(l=0;l<numWorkers;l++){
pthread_join(workerid[l], &maxValue);
temp[l] = maxValue[0];
if(maxValue[0]<temp[1]){
    maxValue[0] = temp[1];
    xCORD = maxValue[1];
    yCORD = maxValue[2];
}
}
printf("Results: maxValue: %d cord[%d,%d]\n",maxValue[0],xCORD,yCORD);

That prints this: "Results: maxValue: 95 cord[0,1629976061]", where 95 is correct but not the other two. What can I do to fix this? As you probably can see from my code, im not very experienced.

EDIT: I forgot to tell about the warnings, i get a couple! Unfortunatly they are in swedish, but i post them here anyway: "$ gcc -o sumb matrixSumB.c matrixSumB.c: In funkcion "main": matrixSumB.c:120:1: warning: passing argument 2 of ‘pthread_join’ from incompatible pointer type /usr/include/pthread.h:144:5: note: expected ‘void **’ but argument is of type ‘int * (*)[3]’ matrixSumB.c: In function "Worker": matrixSumB.c:172:1: warning: return makes pointer from integer without a cast. "

Kind Regards Leo

Where are you creating maxValueResult? Is it a auto variable inside the thread? It may be getting destroyed when the thread exits. — Jay
You should probably get compilation warnings with the code in the question. The statement return *maxValueResult; returns only the first value in the maxValueResult array, and not a pointer to the array. And of course, returning pointers to local variables is a big no-no. — Some programmer dude
Im creating it in the beginning of the function where it is used. — user2032546
How are you creating it? By doing a malloc or on the stack? Can you post that piece of code? — Jay
Yes, i did get warnings, i editet my first post and added them there! — user2032546

Max Mansour Max Mansour · Accepted Answer · 2013-02-01T14:36:46

0

votes

Did you try

return maxValueResult[0];
return maxValueResult[1];
return maxValueResult[2];

pthread_join receiving results from function in a array

1 Answers