update forking example

forking/mutexes.c

@@ -8,45 +8,26 @@
 #include <stdbool.h>
 #include <time.h>
 
-// WARNING: This example does not work, I couldn't figure out why the child process goes into a deadlock on `pthread_mutex_lock`
+// WARNING: This example does not work, I couldn't figure out why the lock does not work correcly.
+// The final counter result should not change, but it does.
 
 struct shared_data {
   pthread_mutex_t mutex;
   int counter;
 };
 
-void milli_sleep(int milliseconds) {
-  struct timespec ts;
-  ts.tv_sec = milliseconds / 1000;
-  ts.tv_nsec = (milliseconds % 1000) * 1000000;
-  nanosleep(&ts, &ts);
-}
-
-float random_float() {
-  return (float)rand()/(float)RAND_MAX;
-}
-
-int random_range(int from, int to) {
-  return random_float()*(to-from) + from;
-}
-
 void run(const char *name, struct shared_data *data) {
-  printf("[%s] started, mutex: %p\n", name, &data->mutex);
+  for (int i = 0; i < 10000; i++) {
-  for (int i = 0; i < 10; i++) {
     if (pthread_mutex_lock(&data->mutex) != 0) {
       perror("pthread_mutex_lock");
     }
 
-    int counter = data->counter;
+    data->counter++;
-    milli_sleep(random_range(0, 100));
-    data->counter = counter + 1;
-    printf("[%s] counter is %d\n", name, counter + 1);
 
     if (pthread_mutex_unlock(&data->mutex) != 0) {
       perror("pthread_mutex_unlock");
     }
   }
-  printf("[%s] finished\n", name);
 }
 
 int main() {
@@ -75,5 +56,7 @@ int main() {
 
   int child_status;
   waitpid(pid, &child_status, 0);
+
+  printf("Counter is %d\n", shared_data->counter);
 }