Task – Threads

Create a program that has an array of numbers of length N. The program should create M threads, each of which will process N/M items in the array. In this case, the “processing” is simply a matter of squaring the numbers. When all threads are complete, the program should display the complete contents of the array.

Solution

Square.cc

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

#include <unistd.h>

void *process_thread( void *ptr );

//N

int numItems=100;

//M

int numThreads=50;

//A counter just to uniquely ID the threads for output

int threadCount=0;

pthread_mutex_t mx = PTHREAD_MUTEX_INITIALIZER;

int main(int argc,char* argv[]){

pthread_t threads[numThreads]; //Store thread IDs

int vals[numItems];

for(int i=0;i<numItems;i++){ //Fill with numbers

vals[i]=i;

}

for(int i=0;i<numThreads;i++){

pthread_create(

&threads[i],

NULL, process_thread,(void*) &vals[i*(numItems/numThreads)]

);

}

for(int i=0;i<numThreads;i++){

pthread_join( threads[i], NULL);

}

return 0;

}

void *process_thread( void *ptr ){

pthread_mutex_lock(&mx);

int myID=threadCount++;

printf(“Thread number %d initialisedn”,myID);

//sleep(1);

for(int i=0;i<(numItems/numThreads);i++){

printf(“(Thread %d) Processing item: was %d “,myID,((int*)ptr)[i]);

//Alternative way to address elements

//printf(“(Thread %d) Processing item: was %d “,myID,*((int*)(ptr+i*sizeof(int))));

//Square the values

((int*)ptr)[i] *= ((int*)ptr)[i];

//No need to worry about other threads printing in between due to the mutex

printf(“now %d n”,((int*)ptr)[i]);

}

//printf(“Val:%dtID:%dn”,val,*((int*)(ptr)));

pthread_mutex_unlock(&mx);

}

Lab Evidence

Source code, with sensible comments showing how the task is complete.

Output of the program showing the threads completing the problem.