112 lines
2.7 KiB
C
112 lines
2.7 KiB
C
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// Write a C program to solve the readers and writers Problem.
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#include <stdio.h>
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#include <stdlib.h>
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#include <pthread.h>
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#include <semaphore.h>
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#include <unistd.h>
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#define NUM_READERS 3
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#define NUM_WRITERS 2
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// shared data structure - simple integer
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int shared_data = 0;
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// sync variables
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pthread_mutex_t mutex; // mutex for read_count protection
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sem_t wrt; // semaphore for writer access control
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int read_count = 0; // tracks active readers
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void* reader(void* arg) {
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int id = *((int*)arg);
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while (1) {
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// read delay sim
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sleep(1);
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// critical section entry
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pthread_mutex_lock(&mutex);
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read_count++;
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if (read_count == 1) {
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// first reader blocks writers
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sem_wait(&wrt);
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}
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pthread_mutex_unlock(&mutex);
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// critical section
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printf("Reader %d is reading shared_data = %d\n", id, shared_data);
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sleep(2); // read time sim
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// critical section exit
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pthread_mutex_lock(&mutex);
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read_count--;
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if (read_count == 0) {
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// last reader unblocks writers
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sem_post(&wrt);
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}
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pthread_mutex_unlock(&mutex);
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}
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pthread_exit(NULL);
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}
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void* writer(void* arg) {
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int id = *((int*)arg);
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while (1) {
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// write delay sim
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sleep(3);
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// critical section entry
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sem_wait(&wrt); // exclusive access control
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// critical section
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shared_data += 1;
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printf("Writer %d is writing: shared_data becomes %d\n", id, shared_data);
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sleep(2); // write time sim
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// critical section exit
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sem_post(&wrt);
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}
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pthread_exit(NULL);
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}
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int main(void) {
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pthread_t readers[NUM_READERS], writers[NUM_WRITERS];
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int reader_ids[NUM_READERS], writer_ids[NUM_WRITERS];
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int i;
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// sync init
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pthread_mutex_init(&mutex, NULL);
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sem_init(&wrt, 0, 1); // binary semaphore init
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// reader thread creation
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for (i = 0; i < NUM_READERS; i++) {
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reader_ids[i] = i + 1;
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if (pthread_create(&readers[i], NULL, reader, &reader_ids[i]) != 0) {
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perror("Failed to create reader thread");
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exit(EXIT_FAILURE);
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}
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}
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// writer thread creation
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for (i = 0; i < NUM_WRITERS; i++) {
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writer_ids[i] = i + 1;
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if (pthread_create(&writers[i], NULL, writer, &writer_ids[i]) != 0) {
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perror("Failed to create writer thread");
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exit(EXIT_FAILURE);
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}
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}
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// thread joining
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for (i = 0; i < NUM_READERS; i++) {
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pthread_join(readers[i], NULL);
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}
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for (i = 0; i < NUM_WRITERS; i++) {
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pthread_join(writers[i], NULL);
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}
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// cleanup
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pthread_mutex_destroy(&mutex);
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sem_destroy(&wrt);
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return 0;
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}
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