From 380c6b7622d8204597b6b23365953ad0ceeb7c9f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Moritz=20=27Morty=27=20Str=C3=BCbe?= <morty@gmx.net>
Date: Tue, 14 Oct 2014 11:09:21 +0200
Subject: [PATCH] Make Random thread safe

---
 .../java/org/contikios/cooja/SafeRandom.java  | 87 +++++++++++++++++++
 .../java/org/contikios/cooja/Simulation.java  |  3 +-
 2 files changed, 89 insertions(+), 1 deletion(-)
 create mode 100644 tools/cooja/java/org/contikios/cooja/SafeRandom.java

diff --git a/tools/cooja/java/org/contikios/cooja/SafeRandom.java b/tools/cooja/java/org/contikios/cooja/SafeRandom.java
new file mode 100644
index 000000000..5dee9c1be
--- /dev/null
+++ b/tools/cooja/java/org/contikios/cooja/SafeRandom.java
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2014, Friedrich-Alexander University Erlangen-Nuremberg.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the university nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ */
+
+package org.contikios.cooja;
+
+import java.util.Random;
+
+/**
+ * This ensures that the functions of the random number generator are
+ * only called by the the thread initializing a simulation or the
+ * simulation thread itself.
+ * Rationale: By allowing another thread to use the random number 
+ * generator concurrency is intruduced, thus it can not be guaranteed 
+ * that simulations are reproduceable.
+ *
+ */
+public class SafeRandom extends Random {
+  
+  Simulation sim = null;
+  Thread initThread = null;
+  
+  private void assertSimThread() {
+    // It we are in the simulation thread everything is fine (the default)
+    // sim can be null, because setSeed is called by the super-constructor.
+    if(sim != null && !sim.isSimulationThread()) {
+      // The thread initializing the simulation might differ from the simulation thread.
+      // If they are the same that is ok, too.
+      if(initThread == null) initThread = Thread.currentThread();
+      if(Thread.currentThread() == initThread ) return;
+      throw new RuntimeException("A random-function was not called from the simulation thread. This can break things!");
+    }
+  }
+  
+  public SafeRandom(Simulation sim) {
+    // assertSimThread is called by the super-constructor.
+    super();
+    this.sim = sim;
+  }
+  
+  public SafeRandom(Simulation sim, long seed) {
+    // assertSimThread is called by the super-constructor.
+    super(seed);
+    this.sim = sim;
+  }
+  
+  synchronized public void setSeed(long seed) {
+    assertSimThread();
+    super.setSeed(seed);
+  }
+  
+  /*
+   * This function is called by all functions returning random numbers
+   * @see java.util.Random#next(int)
+   */
+  protected int next(int bits) {
+    assertSimThread();
+    return super.next(bits);
+  }
+  
+}
diff --git a/tools/cooja/java/org/contikios/cooja/Simulation.java b/tools/cooja/java/org/contikios/cooja/Simulation.java
index 293a4c2c2..18dfa7fe8 100644
--- a/tools/cooja/java/org/contikios/cooja/Simulation.java
+++ b/tools/cooja/java/org/contikios/cooja/Simulation.java
@@ -93,7 +93,7 @@ public class Simulation extends Observable implements Runnable {
 
   private long maxMoteStartupDelay = 1000*MILLISECOND;
 
-  private Random randomGenerator = new Random();
+  private SafeRandom randomGenerator;
 
   private boolean hasMillisecondObservers = false;
   private MillisecondObservable millisecondObservable = new MillisecondObservable();
@@ -322,6 +322,7 @@ public class Simulation extends Observable implements Runnable {
    */
   public Simulation(Cooja cooja) {
     this.cooja = cooja;
+    randomGenerator = new SafeRandom(this);
   }
 
   /**