vault backup: 2025-03-12 11:09:27

Concurrent Systems/notes/4 - Semaphores.md

@@ -101,7 +101,7 @@ B.consume() :=
 B.produce(v) :=
 	FREE.down()
 	SP.down()
-	while not EMPTY[in] do
+	while not EMPTY[in] do # there is at least an EMPTY cell, otherwise it would have been blocked
 		IN <- (IN+1) mod k
 	i <- IN
 	EMPTY[IN] <- ff
@@ -111,5 +111,16 @@ B.produce(v) :=
 	BUSY.up()
 	return
 
-
+B.consume() :=
+	BUSY.down()
+	SC.down()
+	while not FULL[OUT] do
+		OUT <- (OUT+1) mod k
+	o <- OUT
+	FULL[OUT] <- ff
+	SC.up()
+	tmp <- BUF[o]
+	EMPTY[o] <- tt
+	FREE.up()
+	return tmp		
 ```