made it so that zemaphore is used on mac, semaphore on linux, and other clean up

threads-sema/throttle.c

@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "common_threads.h"
+
+#ifdef linux
+#include <semaphore.h>
+#elif __APPLE__
+#include "zemaphore.h"
+#endif
+
+sem_t s;
+
+void *child(void *arg) {
+    Sem_wait(&s); 
+    printf("child %lld\n", (long long int) arg);
+    sleep(1);
+    Sem_post(&s); 
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+	fprintf(stderr, "usage: throttle <num_threads> <sem_value>\n");
+	exit(1);
+    }
+    int num_threads = atoi(argv[1]);
+    int sem_value = atoi(argv[2]);
+    
+    Sem_init(&s, sem_value); 
+
+    printf("parent: begin\n");
+    pthread_t c[num_threads];
+
+    int i;
+    for (i = 0; i < num_threads; i++) 
+	Pthread_create(&c[i], NULL, child, (void *) (long long int)i);
+
+    for (i = 0; i < num_threads; i++) 
+	Pthread_join(c[i], NULL);
+
+    printf("parent: end\n");
+    return 0;
+}
+