Updates from lab.

semaphore.h

@@ -45,7 +45,7 @@ private:
   /* -- INTERNAL DATA STRUCTURES
      You may need to change them to fit your implementation. */
 
-  int             value;
+  int value;
   pthread_mutex_t m;
   pthread_cond_t  c;
 
@@ -53,18 +53,25 @@ public:
 
   /* -- CONSTRUCTOR/DESTRUCTOR */
 
-  Semaphore(int _val){value = _val;}
+  Semaphore(int _val){
+    value = _val;
+    pthread_mutex_init(&m);
+    pthread_cond_init(&c);
+  }
 
   ~Semaphore(){}
 
   /* -- SEMAPHORE OPERATIONS */
 
-  int P(){
+  int P() {
     //This is to lock the Semaphore.
     pthread_mutex_lock( &m );
     
-    //Wait until condition, basically wait until signaled.
-    pthread_cond_wait( &c, &m );
+    --value;
+    //If counter is negative, wait until condition, basically wait until signaled.
+    if(value < 0) {
+      pthread_cond_wait( &c, &m );
+    }
 
     //Some code here.
 
@@ -72,7 +79,17 @@ public:
     pthread_mutex_unlock( &m );
   }
       //;
-  int V();
+  int V() {
+    pthread_mutex_lock( &m );
+    
+    ++value;
+
+    if(value <= 0) {
+      pthread_cond_signal( &c );
+    }
+    
+    pthread_mutex_unlock( &m );
+  }
 };
 
 /*