Data commit

Task/Metered-concurrency/C/metered-concurrency.c

@@ -0,0 +1,51 @@
+#include <semaphore.h>
+#include <pthread.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+sem_t sem;
+int count = 3;
+
+/* the whole point of a semaphore is that you don't count it:
+ * p/v are atomic.  Unless it's locked while you are doing
+ * something with the count, the value is only informative */
+#define getcount() count
+void acquire()
+{
+	sem_wait(&sem);
+	count--;
+}
+
+void release()
+{
+	count++;
+	sem_post(&sem);
+}
+
+void* work(void * id)
+{
+	int i = 10;
+	while (i--) {
+		acquire();
+		printf("#%d acquired sema at %d\n", *(int*)id, getcount());
+		usleep(rand() % 4000000); /* sleep 2 sec on average */
+		release();
+		usleep(0);  /* effectively yield */
+	}
+	return 0;
+}
+
+int main()
+{
+	pthread_t th[4];
+	int i, ids[] = {1, 2, 3, 4};
+
+	sem_init(&sem, 0, count);
+
+	for (i = 4; i--;) pthread_create(th + i, 0, work, ids + i);
+	for (i = 4; i--;) pthread_join(th[i], 0);
+	printf("all workers done\n");
+
+	return sem_destroy(&sem);
+}