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

.obsidian/workspace.json

@@ -13,12 +13,12 @@
             "state": {
               "type": "markdown",
               "state": {
-                "file": "Concurrent Systems/notes/4b -.md",
+                "file": "Concurrent Systems/notes/4c - Dining Philosophers.md",
                 "mode": "source",
                 "source": false
               },
               "icon": "lucide-file",
-              "title": "4b -"
+              "title": "4c - Dining Philosophers"
             }
           }
         ]
@@ -34,9 +34,9 @@
               "type": "pdf",
               "state": {
                 "file": "Concurrent Systems/slides/class 4.pdf",
-                "page": 16,
+                "page": 17,
                 "left": -27,
-                "top": 130,
+                "top": 78,
                 "zoom": 0.5754156769596199
               },
               "icon": "lucide-file-text",
@@ -218,8 +218,9 @@
   },
   "active": "6edd4157a160e462",
   "lastOpenFiles": [
+    "Concurrent Systems/notes/4b - Monitors.md",
+    "Concurrent Systems/notes/4c - Dining Philosophers.md",
     "Concurrent Systems/slides/class 4.pdf",
-    "Concurrent Systems/notes/4b -.md",
     "Concurrent Systems/slides/class 5.pdf",
     "HCIW/slides/4 HUI2016-6-forcefeedback.pdf",
     "HCIW/slides/3b Haptic slides.pdf",

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