readme

Author: wolfram77

MCSLock.java

@@ -33,8 +33,9 @@ protected QNode initialValue() {
     };
   }
 
-  // 1. When thread wants to access critical section,
-  //    it stands at the end of the queue (FIFO).
+  // 1. When thread wants to access critical
+  //    section, it stands at the end of the
+  //    queue (FIFO).
   // 2a. If there is no one in queue, it goes head
   //     with its critical section.
   // 2b. Otherwise, it locks itself and asks the

README.md

@@ -0,0 +1,49 @@
+MCS Queue Lock maintains a linked-list for
+threads waiting to enter critical section (CS).
+
+Each thread that wants to enter CS joins at the
+end of the queue, and waits for the thread
+infront of it to finish its CS.
+So, it locks itself and asks the thread infront
+of it, to unlock it when he's done. Atomics
+instructions are used when updating the shared
+queue. Corner cases are also takes care of.
+
+As each thread waits (spins) on its own "locked"
+field, this type of lock is suitable for
+cache-less NUMA architectures.
+
+```java
+1. When thread wants to access critical
+   section, it stands at the end of the
+   queue (FIFO).
+2a. If there is no one in queue, it goes head
+    with its critical section.
+2b. Otherwise, it locks itself and asks the
+    thread infront of it to unlock it when its
+    done with CS.
+```
+
+```java
+1. When a thread is done with its critical
+   section, it needs to unlock any thread
+   standing behind it.
+2a. If there is a thread standing behind,
+    then it unlocks him.
+2b. Otherwise it tries to mark queue as empty.
+     If no one is joining, it leaves.
+2c. If there is a thread trying to join the
+    queue, it waits until he is done, and then
+    unlocks him, and leaves.
+```
+
+See [MCSLock.java] for code, [Main.java] for test, and [repl.it] for output.
+
+[MCSLock.java]: https://repl.it/@wolfram77/mcs-lock#MCSLock.java
+[Main.java]: https://repl.it/@wolfram77/mcs-lock#Main.java
+[repl.it]: https://mcs-lock.wolfram77.repl.run
+
+
+### references
+
+- [The Art of Multiprocessor Programming :: Maurice Herlihy, Nir Shavit](https://dl.acm.org/doi/book/10.5555/2385452)