77 lines
1.7 KiB
C
77 lines
1.7 KiB
C
/*
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* pthreads6.c - Shows the problems that can happen due to the fact
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* that thread routine parameters are pointers to memory
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* locations. Threads can easily affect other threads
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* memory.
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*
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* NOTE: Context switches between threads can happen when unexpected
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*/
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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// Function to check if a number is prime
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// Returns 1 if prime, 0 if not prime
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int is_prime(int v)
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{
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for (int i = 2; i < v; i++)
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{
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if (v % i == 0)
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{
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return 0;
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}
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}
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return 1;
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}
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// Thread routine
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// calls is_prime to check if the input argument is prime
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// Modifies the input parameter by dereferencing the pointer
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//
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// NOTE: that parameters and return value are pointers
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void *thread_routine(void *args)
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{
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int *val = (int *)args;
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if (is_prime(*val))
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{
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printf("THREAD %lu FOUND that %d is prime %p\n", pthread_self(), *val, val);
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*val = 1;
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}
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else
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{
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printf("THREAD %lu FOUND that %d is not prime %p\n", pthread_self(), *val, val);
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*val = 0;
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}
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return NULL;
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}
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int main()
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{
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int val = 0;
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// Create 10 threads
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pthread_t thr[10];
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for (int i = 0; i < 10; i++)
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{
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// NOTE: there is a single memory location for val which is passed to all threads
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val = i + 2;
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if (pthread_create(&thr[i], NULL, thread_routine, (void *)&val) == -1)
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{
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printf("COULD NOT CREATE A THREAD\n");
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exit(EXIT_FAILURE);
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}
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}
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// Wait for threads to finish
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for (int i = 0; i < 10; i++)
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{
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pthread_join(thr[i], NULL);
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}
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// Return success
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return 0;
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}
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