From 8bb915ce5c8f8c1c5d687c0d0df8e49250cd670a Mon Sep 17 00:00:00 2001
From: Luca Conte <main@lugico.de>
Date: Wed, 23 Apr 2025 23:17:29 +0200
Subject: [PATCH] u06-5

---
 u06-5/Concurrent.java   | 26 ++++++++++++++++++++++++++
 u06-5/SpinLock.java     | 20 ++++++++++++++++++++
 u06-5/SpinLockTest.java | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 82 insertions(+)
 create mode 100644 u06-5/Concurrent.java
 create mode 100644 u06-5/SpinLock.java
 create mode 100644 u06-5/SpinLockTest.java

diff --git a/u06-5/Concurrent.java b/u06-5/Concurrent.java
new file mode 100644
index 0000000..5c35d05
--- /dev/null
+++ b/u06-5/Concurrent.java
@@ -0,0 +1,26 @@
+abstract class Concurrent<ArgType> {
+	private ArgType[] args;
+
+	public Concurrent(ArgType[] args) {
+		this.args = args;
+	}
+
+	void run() {
+		Thread[] threads = new Thread[args.length];
+
+		for (int i = 0; i < args.length; i++) {
+			final ArgType arg = args[i];
+			threads[i] = new Thread(() -> perform(arg));
+			threads[i].start();
+		}
+		for (int i = 0; i < threads.length; i++) {
+			try {
+				threads[i].join();
+			} catch (InterruptedException e) {
+				e.printStackTrace();
+			}
+		}
+	}
+
+	abstract void perform(ArgType arg);
+}
\ No newline at end of file
diff --git a/u06-5/SpinLock.java b/u06-5/SpinLock.java
new file mode 100644
index 0000000..d0014ef
--- /dev/null
+++ b/u06-5/SpinLock.java
@@ -0,0 +1,20 @@
+import java.util.concurrent.atomic.AtomicReference;
+
+class SpinLock {
+	private AtomicReference<Thread> currentThread;
+
+	public SpinLock() {
+		currentThread = new AtomicReference<Thread>(null);
+	}
+
+	public void lock() {
+		Thread thisThread = Thread.currentThread();
+
+		// wait for currentThread to be null to acquire lock
+		while (!currentThread.compareAndSet(null, thisThread));
+	}
+
+	public boolean unlock() {
+		return currentThread.compareAndSet(Thread.currentThread(), null);
+	}
+}
\ No newline at end of file
diff --git a/u06-5/SpinLockTest.java b/u06-5/SpinLockTest.java
new file mode 100644
index 0000000..dd907fb
--- /dev/null
+++ b/u06-5/SpinLockTest.java
@@ -0,0 +1,36 @@
+class SpinLockTest extends Concurrent<SpinLock> {
+	
+	SpinLockTest(SpinLock[] args) {
+		super(args);
+	}
+	protected void perform(SpinLock lock) {
+		System.out.println(Thread.currentThread().getName() + 
+				" wartet auf das Lock...");
+		lock.lock();
+
+		System.out.println(Thread.currentThread().getName() + 
+				" hat das Lock und behält es für etwa 1 Sek....");
+	    try {
+	    	Thread.sleep((long) (500 + Math.random()*1000));
+	    } catch (InterruptedException e) {
+	    	// Beim Schlafen zufaelliger Dauer unterbrochen zu werden ist kein Schaden
+	    }
+
+		if (lock.unlock()) {
+		    System.out.println(Thread.currentThread().getName() + 
+				" hat das von ihm vorher gesperrte Lock freigegeben und endet.");
+		} else {
+			System.out.println(Thread.currentThread().getName() + 
+					" hat das Lock schon freigegeben vorgefunden!?");
+		}
+			
+	}
+	
+	public static void main(String[] args) {
+		SpinLock sl = new SpinLock(); 
+		SpinLock[] locks = {sl, sl, sl, sl, sl}; 
+					       // alle Threads benutzen dasselbe SpinLock sl
+		new SpinLockTest(locks).run();
+	}
+}
+