vault backup: 2025-03-12 12:19:27

Concurrent Systems/notes/4 - Semaphores.md

@@ -162,18 +162,26 @@ producer A:
 - ...
 - writes at BUF[n], so IN becomes 0
 
+**Now there are no free slots.**
+
 consumer A:
 - starts reading BUF[0], now OUT is 1
+	- it is a sloooooooooow consumer
 
 consumer B:
-- finds OUT at 1
-- sets OUT at 2 and starts reading
-- finishes reading
+- finds OUT at 1, sets OUT at 2 and starts reading
+- finishes reading (before consumer A)
 - sets EMPTY[1] <- tt
+- calls `FREE.up()`
 
-consumer A:
-- finishes reading (finally)
-- sets EMPTY[0] <- tt
+producer A:
+- as consumer B called `FREE.up()`, the producer can finally produce
+- remember, IN is set to 0!
+- so producer A will write at `BUF[0]`
+- but wait! Consumer B is still reading there
+- **Producer A doesn't give a fuck.**
+	![[Pasted image 20250312121828.png|200]]
+	*don't be like Producer A, be more like Bob*