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

threads-sema/zemaphore.h

@@ -0,0 +1,37 @@
+#ifndef __zemaphore_h__
+#define __zemaphore_h__
+
+typedef struct __Zem_t {
+    int value;
+    pthread_cond_t  cond;
+    pthread_mutex_t lock;
+} Zem_t;
+
+void Zem_init(Zem_t *z, int value) {
+    z->value = value;
+    Cond_init(&z->cond);
+    Mutex_init(&z->lock);
+}
+
+void Zem_wait(Zem_t *z) {
+    Mutex_lock(&z->lock);
+    while (z->value <= 0)
+	Cond_wait(&z->cond, &z->lock);
+    z->value--;
+    Mutex_unlock(&z->lock);
+}
+
+void Zem_post(Zem_t *z) {
+    Mutex_lock(&z->lock);
+    z->value++;
+    Cond_signal(&z->cond);
+    Mutex_unlock(&z->lock);
+}
+
+typedef Zem_t sem_t;
+
+#define Sem_wait(s)    Zem_wait(s)
+#define Sem_post(s)    Zem_post(s)
+#define Sem_init(s, v) Zem_init(s, v)
+
+#endif // __zemaphore_h__