From d9584646389001606626e1517ea6abb5e38ca455 Mon Sep 17 00:00:00 2001
From: Vladyslav Karpenko <klarpen@gmail.com>
Date: Tue, 14 Feb 2023 17:22:40 +0200
Subject: [PATCH] Enhance livelock example

More complex but clear to notice livelock test:
- 7 threads
- 6 of it executes high frequency loop
- last 7th thread executes low frequency loop with long running process
- initial 10 times frequency difference do not lead to livelock
- comment with proposal to make frequency difference 100 times higher
which will lead to livelock

Signed-off-by: Vladyslav Karpenko <klarpen@gmail.com>
---
 JavaScript/3-livelock.js | 41 +++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/JavaScript/3-livelock.js b/JavaScript/3-livelock.js
index 70ce7bd..373df06 100644
--- a/JavaScript/3-livelock.js
+++ b/JavaScript/3-livelock.js
@@ -3,6 +3,8 @@
 const threads = require('node:worker_threads');
 const { Worker, isMainThread } = threads;
 
+const THREADS_COUNT = 7;
+
 const LOCKED = 0;
 const UNLOCKED = 1;
 
@@ -37,24 +39,49 @@ if (isMainThread) {
   const mutex1 = new Mutex(buffer, 0, true);
   const mutex2 = new Mutex(buffer, 4, true);
   console.dir({ mutex1, mutex2 });
-  new Worker(__filename, { workerData: buffer });
-  new Worker(__filename, { workerData: buffer });
+  for (let i = 0; i < THREADS_COUNT; i++) new Worker(__filename, { workerData: buffer });
 } else {
   const { threadId, workerData } = threads;
   const mutex1 = new Mutex(workerData);
   const mutex2 = new Mutex(workerData, 4);
 
-  const loop = () => {
+  const lowFrequencyLoop = (delay) => {
+    mutex1.enter(() => {
+      console.log(`Some useful processing from worker${threadId} based on data locked by mutex1`);
+      mutex2.enter(() => {
+        console.log(`Some useful processing from worker${threadId} based on data locked by mutex2`);
+        setTimeout(() => {
+          mutex1.leave();
+          console.log(`Left mutex1 from worker${threadId} after some useful process has been done`);
+          mutex2.leave();
+          console.log(`Left mutex2 from worker${threadId} after some useful process has been done`);
+          setTimeout(lowFrequencyLoop, delay, delay);
+        }, 2000);
+      });
+    });
+  };
+
+  const highFrequencyLoop = (delay) => {
     mutex1.enter(() => {
       console.log(`Entered mutex1 from worker${threadId}`);
-      if (mutex1.leave()) console.log(`Left mutex1 from worker${threadId}`);
+      mutex1.leave();
+      console.log(`Left mutex1 from worker${threadId}`);
     });
     mutex2.enter(() => {
       console.log(`Entered mutex2 from worker${threadId}`);
-      if (mutex2.leave()) console.log(`Left mutex2 from worker${threadId}`);
+      mutex2.leave();
+      console.log(`Left mutex2 from worker${threadId}`);
     });
-    setTimeout(loop, 0);
+    setTimeout(highFrequencyLoop, delay, delay);
   };
-  loop();
 
+  if (threadId === THREADS_COUNT) {
+    // Only one thread executes low frequent process
+    lowFrequencyLoop(1000);
+  } else {
+    // All other threads executes high frequent processes
+    highFrequencyLoop(100);
+    // Try to change delay between iterations to 1 ms
+    // Look out how livelock preventing useful low frequent process to get access on data locked by Mutex
+  }
 }