From 8e1ea33ab8170ecf5b8a988cffc648dd37339d29 Mon Sep 17 00:00:00 2001
From: Marco Realacci <marco@marcorealacci.me>
Date: Mon, 17 Mar 2025 10:04:23 +0100
Subject: [PATCH] vault backup: 2025-03-17 10:04:23

---
 .obsidian/workspace.json                             | 11 ++++++-----
 .../notes/{4b -.md => 4b - Monitors.md}              | 12 ++++++------
 Concurrent Systems/notes/4c - Dining Philosophers.md |  6 ++++++
 3 files changed, 18 insertions(+), 11 deletions(-)
 rename Concurrent Systems/notes/{4b -.md => 4b - Monitors.md} (97%)
 create mode 100644 Concurrent Systems/notes/4c - Dining Philosophers.md

diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index 01f0c24..94c1b9c 100644
--- a/.obsidian/workspace.json
+++ b/.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",
diff --git a/Concurrent Systems/notes/4b -.md b/Concurrent Systems/notes/4b - Monitors.md
similarity index 97%
rename from Concurrent Systems/notes/4b -.md
rename to Concurrent Systems/notes/4b - Monitors.md
index 2b63763..a5362e1 100644
--- a/Concurrent Systems/notes/4b -.md	
+++ b/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.
\ No newline at end of file
diff --git a/Concurrent Systems/notes/4c - Dining Philosophers.md b/Concurrent Systems/notes/4c - Dining Philosophers.md
new file mode 100644
index 0000000..d4c017d
--- /dev/null
+++ b/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
\ No newline at end of file