From b0a41846813be1a4248e717539efc20acadd1719 Mon Sep 17 00:00:00 2001
From: Marco Realacci <marco@marcorealacci.me>
Date: Mon, 17 Mar 2025 09:34:23 +0100
Subject: [PATCH] vault backup: 2025-03-17 09:34:23

---
 .obsidian/workspace.json         |  8 ++++----
 Concurrent Systems/notes/4b -.md | 12 +++++++++++-
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/.obsidian/workspace.json b/.obsidian/workspace.json
index 611348c..e6a430b 100644
--- a/.obsidian/workspace.json
+++ b/.obsidian/workspace.json
@@ -34,9 +34,9 @@
               "type": "pdf",
               "state": {
                 "file": "Concurrent Systems/slides/class 4.pdf",
-                "page": 12,
+                "page": 13,
                 "left": -27,
-                "top": 16,
+                "top": 96,
                 "zoom": 0.5754156769596199
               },
               "icon": "lucide-file-text",
@@ -216,10 +216,10 @@
       "companion:Toggle completion": false
     }
   },
-  "active": "6edd4157a160e462",
+  "active": "071b6cd23e4b1e9d",
   "lastOpenFiles": [
-    "Concurrent Systems/slides/class 4.pdf",
     "Concurrent Systems/notes/4b -.md",
+    "Concurrent Systems/slides/class 4.pdf",
     "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 -.md
index 0909ae3..6c99f96 100644
--- a/Concurrent Systems/notes/4b -.md	
+++ b/Concurrent Systems/notes/4b -.md	
@@ -25,5 +25,15 @@ monitor RNDV :=
 		B.signal()
 		return
 ```
-The last process wakes up one of the others... Then he wakes up another one etc...
+The last process wakes up one of the others, then he wakes up another one etc...
+Of course, `signal()` will have no effect on the last process who calls it.
 
+#### Monitor implementation through semaphores
+*Hoare semantics*
+
+- A semaphore MUTEX init at 1 (to guarantee mutex in the monitor)
+- For every condition C, a semaphore SEMC init at 0 and an integer $N_{C}$ init at 0 (to store and count the number of suspended processes on the given condition)
+- A semaphore PRIO init at 0 and an integer $N_{PR}$ init at 0 (to store and count the number of processes that have performed a signal, and so have priority to re-enter the monitor)
+
+1. Every monitor operation starts with `MUTEX.down()` and ends with `if NPR > 0 then PRIO.up() else MUTEX.up()`
+2. 
\ No newline at end of file