vault backup: 2025-03-17 10:04:23

Concurrent Systems/notes/4b - Monitors.md

@@ -1,4 +1,3 @@
-### Monitors
 Semaphores are hard to use in practice because quite low level Monitors provide an easier definition of concurrent objects at the level of Prog. Lang.
 
 It guarantees mutual exclusion.
@@ -109,7 +108,7 @@ operation end_read() :=
 
 operation begin_write() :=
 	WW++
-	if (AR+AW != 0) then
+	if (AR + AW != 0) then
 		CW.wait()
 	AW++
 	WW--
@@ -145,15 +144,16 @@ operation end_read() :=
 
 operation begin_write() :=
 	WW++
-	if (AR+AW != 0) then
+	if (AR + AW != 0) then
 		CW.wait()
 	AW++
 	WW--
 
 operation end_write() :=
 	AW--
-	if WW > 0 then
-		CW.signal()
-	else
+	if WR > 0 then
 		CR.signal()
+	else
+		CW.signal()
 ```
+This way nobody gets starved forever.

Concurrent Systems/notes/4c - Dining Philosophers.md

@@ -0,0 +1,6 @@
+The first real practical example of a concurrent system.
+
+- $N$ philosophers seated around a circular table
+- one chopstick between each pair of philosophers
+- a philosophers must pick up its two nearest chopsticks in order to eat
+- a philosoph