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reader_writer.c
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reader_writer.c
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#include <semaphore.h>
#include <stdio.h>
#include <stdbool.h>
#include <pthread.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#define NUM_READERS 15
#define NUM_WRITERS 2
#define MAX_WAITING_TIME 10
#define MAX_READING_TIME 2
#define MAX_WRITING_TIME 8
sem_t sem_w;
sem_t sem_r;
int active_readers;
void* reader(void* p) {
int reader_id = *((int*)p);
while(true) {
sleep(rand()%MAX_WAITING_TIME);
sem_wait(&sem_r);
if(active_readers == 0) {
sem_wait(&sem_w);
}
active_readers += 1;
sem_post(&sem_r);
printf("reader %d started reading...\n", reader_id);
sleep(rand()%MAX_READING_TIME);
printf("... reader %d ended reading\n", reader_id);
sem_wait(&sem_r);
active_readers -= 1;
if(active_readers == 0) {
sem_post(&sem_w);
}
sem_post(&sem_r);
}
}
void* writer(void* p) {
int reader_id = *((int*)p);
while(true) {
sleep(rand()%MAX_WAITING_TIME);
sem_wait(&sem_w);
printf("\twriter %d started writing...\n", reader_id);
sleep(rand()%MAX_WRITING_TIME);
printf("\t... writer %d ended writing\n", reader_id);
sem_post(&sem_w);
}
}
int main() {
srand(time(NULL));
sem_init(&sem_w, 0, 1);
sem_init(&sem_r, 0, 1);
pthread_t readers[NUM_READERS];
for(int i = 0; i < NUM_READERS; i++) {
int* arg = malloc(sizeof(int));
*arg = i; //PASS READER ID TO THREAD
if(pthread_create(&readers[i], NULL, reader, arg) != 0) {
fprintf(stderr, "Error creating reader thread\n");
return 1;
}
}
pthread_t writers[NUM_WRITERS];
for(int i = 0; i < NUM_WRITERS; i++) {
int* arg = malloc(sizeof(int));
*arg = i;
if(pthread_create(&writers[i], NULL, writer, arg) != 0) {
fprintf(stderr, "Error creating writer thread\n");
return 1;
}
}
for(int i = 0; i < NUM_READERS; i++) {
if(pthread_join(readers[i], NULL) != 0) {
fprintf(stderr, "Error joining reader thread\n");
return 1;
}
}
for(int i = 0; i < NUM_WRITERS; i++) {
if(pthread_join(writers[i], NULL) != 0) {
fprintf(stderr, "Error joining writer thread\n");
return 1;
}
}
sem_destroy(&sem_w);
sem_destroy(&sem_r);
return 0;
}