vault backup: 2025-03-12 10:54:27

.obsidian/workspace.json

@@ -36,7 +36,7 @@
                 "file": "Concurrent Systems/slides/class 4.pdf",
                 "page": 4,
                 "left": -23,
-                "top": 342,
+                "top": 187,
                 "zoom": 0.652019002375297
               },
               "icon": "lucide-file-text",

Concurrent Systems/notes/4 - Semaphores.md

@@ -71,4 +71,21 @@ Same as before but we use test&set to actually ensure MUTEX (of course we could
 It's a shared FIFO buffer of size k.
 - `BUF[0,…,k-1]`: generic registers (not even safe) accessed in MUTEX
 - `IN/OUT` : two variables pointing to locations in `BUF` to (circularly) insert/remove items, both initialized at 0
-- `FREE/BUSY`: two semaphores that count thew number of free/busy cells of BUF, initialized at k and 0 respectively.
+- `FREE/BUSY`: two semaphores that count thew number of free/busy cells of `BUF`, initialized at k and 0 respectively.
+
+```
+B.produce(v) :=
+	FREE.down() # blocking if FREE becomes negative
+	BUF[IN] <- v
+	IN <- (IN+1) mod k # mod k since it is circular
+	BUSY.up() # "there is something to consume"
+	return
+
+B.consume() :=
+	BUSY.down() # it blocks if there is nothing to consume
+	tmp <- BUF[OUT]
+	OUT <- (OUT+1) mod k
+	FREE.up()
+	return tmp
+```
+