[Android] Fix race condition in BaseTestServer.

net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java

Index: net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java
diff --git a/net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java b/net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java
index a9ca6bd6173c71caa9109e36a93fed265bc5ef00..0d226980d31dd8ddb7b231b5328da5ad466e1ea4 100644
--- a/net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java
+++ b/net/test/android/javatests/src/org/chromium/net/test/BaseTestServer.java
@@ -4,34 +4,69 @@
 
 package org.chromium.net.test;
 
+import org.chromium.base.Log;
+
 import java.util.concurrent.atomic.AtomicBoolean;
 
 /** A base class for simple test servers. */
 public abstract class BaseTestServer implements Runnable {
+    private static final String TAG = Log.makeTag("net.test");
+
     private AtomicBoolean mKeepRunning;
+    private final Object mLock;
+    private boolean mRunning;
 
     /** Creates a test server. */
     public BaseTestServer() {
         mKeepRunning = new AtomicBoolean(true);
+        mLock = new Object();
     }
 
     /** Accepts incoming connections until stopped via stop(). */
     public void run() {
-        mKeepRunning.set(true);
+        serverHasStarted();
 
-        while (mKeepRunning.get()) {
-            accept();
+        try {
+            while (mKeepRunning.get()) {
+                accept();
+            }
+        } finally {
+            serverHasStopped();
         }
     }
 
-    /** Waits for and handles an incoming request. */
-    protected abstract void accept();
+    /** Waits for the server to start. */
+    public void waitForServerToStart() {
+        synchronized (mLock) {
+            while (!mRunning) {
+                try {
+                    mLock.wait();
+                } catch (InterruptedException e) {
+                    Log.e(TAG, "Interrupted while waiting for server to stop.", e);
+                }
+            }
+        }
+    }
 
-    /** Returns the port on which this server is listening for connections. */
-    public abstract int getServerPort();
+    private void serverHasStarted() {
+        synchronized (mLock) {

[mef, 2015/05/07 15:59:56]

If this method is called after waitForServerToStart(), then this will be waiting
for the lock held in waitForServerToStart().

[nyquist, 2015/05/07 16:37:25]

When wait is invoked, the thread releases the lock and suspends execution.

The part inside synchronized(THIS_OBJECT) must match the THIS_OBJECT.wait() and
THIS_OBJECT.notify() for this to work correctly.

See http://developer.android.com/reference/java/lang/Object.html#wait() or 
See https://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html
for some more helpful concurrency documentation.

+            mRunning = true;
+            mLock.notifyAll();
+        }
+    }
 
     /** Stops the server. */
     public void stop() {
         mKeepRunning.set(false);
     }
+
+    /** Waits for and handles an incoming request. */
+    protected abstract void accept();
+
+    private void serverHasStopped() {
+        synchronized (mLock) {
+            mRunning = false;
+            mLock.notifyAll();
+        }
+    }
 }