80 lines
1.8 KiB
C
80 lines
1.8 KiB
C
#include <string.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include <sys/wait.h>
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#include <pthread.h>
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#include <stdbool.h>
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#include <time.h>
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// WARNING: This example does not work, I couldn't figure out why the child process goes into a deadlock on `pthread_mutex_lock`
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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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void milli_sleep(int milliseconds) {
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struct timespec ts;
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ts.tv_sec = milliseconds / 1000;
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ts.tv_nsec = (milliseconds % 1000) * 1000000;
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nanosleep(&ts, &ts);
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}
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float random_float() {
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return (float)rand()/(float)RAND_MAX;
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}
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int random_range(int from, int to) {
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return random_float()*(to-from) + from;
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}
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void run(const char *name, struct shared_data *data) {
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printf("[%s] started, mutex: %p\n", name, &data->mutex);
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for (int i = 0; i < 10; 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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int counter = data->counter;
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milli_sleep(random_range(0, 100));
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data->counter = counter + 1;
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printf("[%s] counter is %d\n", name, counter + 1);
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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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printf("[%s] finished\n", name);
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}
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int main() {
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struct shared_data *shared_data = mmap(NULL, sizeof(struct shared_data), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
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if (shared_data == NULL) {
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perror("mmap");
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return -1;
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}
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if (pthread_mutex_init(&shared_data->mutex, NULL) < 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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shared_data->counter = 0;
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int pid = fork();
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if (pid == 0) {
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srand(time(NULL)+1);
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run("Child ", shared_data);
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return 0;
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} else {
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srand(time(NULL)+2);
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run("Parent", shared_data);
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}
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int child_status;
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waitpid(pid, &child_status, 0);
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}
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