123 lines
2.7 KiB
C
123 lines
2.7 KiB
C
#include <sys/mman.h>
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#include <fcntl.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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#include <pthread.h>
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#include <stdbool.h>
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#define SHM_NAME "/shared_memory"
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struct shared_data {
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pthread_mutex_t mutex;
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int counter;
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};
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struct shm_shared_data {
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int shm_fd;
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struct shared_data *shared_data;
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};
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void increment_counter(struct shared_data *data) {
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for (int i = 0; i < 100000; i++) {
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if (pthread_mutex_lock(&data->mutex) != 0) {
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perror("pthread_mutex_lock");
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}
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data->counter++;
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if (pthread_mutex_unlock(&data->mutex) != 0) {
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perror("pthread_mutex_unlock");
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}
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}
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}
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struct shm_shared_data shared_data_open() {
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struct shared_data *shared_data;
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// Create or open a shared memory object
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int shm_fd = shm_open(SHM_NAME, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
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if (shm_fd == -1) {
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perror("shm_open");
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exit(EXIT_FAILURE);
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}
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int shm_size = sizeof(struct shared_data);
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if (ftruncate(shm_fd, shm_size) == -1) {
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perror("ftruncate");
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exit(EXIT_FAILURE);
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}
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// Map the shared memory object into the process's address space
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shared_data = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
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if (shared_data == MAP_FAILED) {
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perror("mmap");
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exit(EXIT_FAILURE);
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}
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struct shm_shared_data shm_shared_data = {
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.shm_fd = shm_fd,
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.shared_data = shared_data
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};
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return shm_shared_data;
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}
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void shared_data_close(struct shm_shared_data shm_data) {
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// Unmap the shared memory and close the file descriptor
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if (munmap(shm_data.shared_data, sizeof(struct shared_data)) == -1) {
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perror("munmap");
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exit(EXIT_FAILURE);
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}
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if (close(shm_data.shm_fd) == -1) {
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perror("close");
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exit(EXIT_FAILURE);
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}
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}
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void *thread_callback(void *p) {
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struct shm_shared_data shm_data = shared_data_open();
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increment_counter(shm_data.shared_data);
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shared_data_close(shm_data);
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return NULL;
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}
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int main() {
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struct shm_shared_data shm_data = shared_data_open();
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pthread_mutexattr_t mutex_attr;
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pthread_mutexattr_init(&mutex_attr);
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pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED);
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if (pthread_mutex_init(&shm_data.shared_data->mutex, &mutex_attr) < 0) {
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printf("Failed to initialise mutex\n");
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return -1;
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}
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pthread_t thread1;
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pthread_create(&thread1, NULL, thread_callback, NULL);
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pthread_t thread2;
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pthread_create(&thread2, NULL, thread_callback, NULL);
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pthread_join(thread1, NULL);
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pthread_join(thread2, NULL);
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printf("Counter is %d\n", shm_data.shared_data->counter);
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shared_data_close(shm_data);
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// Unlink the shared memory object (aka delete shared memory)
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if (shm_unlink(SHM_NAME) == -1) {
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perror("shm_unlink");
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exit(EXIT_FAILURE);
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}
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return 0;
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}
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