73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
/*
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* pthreads5.c - Shows a problem that can happen with parameters
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* passed to thread routines due to the fact that
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* the parameter must be a pointer. The referenced
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* location must be valid for the entire life of the
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* thread.
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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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//
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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\n", pthread_self(), *val);
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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\n", pthread_self(), *val);
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}
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return NULL;
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}
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// start_thread
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// Creates a new thread and returns the thread ID
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//
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// NOTE: the parameter to the thread is created on the stack
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// the address becomes invalid when the function returns
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pthread_t start_thread(int val)
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{
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pthread_t thr;
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printf("Before thread creation val=%d\n", val);
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if (pthread_create(&thr, 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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return thr;
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}
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int main()
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{
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pthread_t thr1 = start_thread(2);
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pthread_t thr2 = start_thread(100);
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pthread_join(thr1, NULL);
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pthread_join(thr2, NULL);
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return 0;
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}
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