android: Java-based launcher thread

base/android/java/src/org/chromium/base/JavaHandlerThread.java

Index: base/android/java/src/org/chromium/base/JavaHandlerThread.java
diff --git a/base/android/java/src/org/chromium/base/JavaHandlerThread.java b/base/android/java/src/org/chromium/base/JavaHandlerThread.java
index cd057282b88513b4cc48d3d70b16978b9ac58849..cb44008539f3ae25ed6dbd45d14b9e64c88fa47d 100644
--- a/base/android/java/src/org/chromium/base/JavaHandlerThread.java
+++ b/base/android/java/src/org/chromium/base/JavaHandlerThread.java
@@ -8,19 +8,24 @@ import android.annotation.TargetApi;
 import android.os.Build;
 import android.os.Handler;
 import android.os.HandlerThread;
+import android.os.Looper;
 
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 
 /**
- * This class is an internal detail of the native counterpart.
- * It is instantiated and owned by the native object.
+ * Thread in Java with an Anroid Handler. This class is not thread safe.
  */
 @JNINamespace("base::android")
-class JavaHandlerThread {
-    final HandlerThread mThread;
+public class JavaHandlerThread {
+    private final HandlerThread mThread;
+    private boolean mStarted;
 
-    private JavaHandlerThread(String name) {
+    /**
+     * Construct a java-only instance. Can be connected with native side later.
+     * Useful for cases where a java thread is needed before native library is loaded.
+     */
+    public JavaHandlerThread(String name) {
         mThread = new HandlerThread(name);
     }
 
@@ -29,9 +34,19 @@ class JavaHandlerThread {
         return new JavaHandlerThread(name);
     }
 
-    @CalledByNative
-    private void start(final long nativeThread, final long nativeEvent) {
+    public Looper getLooper() {

[agrieve, 2017/03/28 19:59:32]

super nit: Might make more sense to expose this by having JavaHandlerThread
extend HandlerThread. Normally I prefer composition, but from the name I think
one would expect JavaHandlerThread instanceof HandlerThread.

[boliu, 2017/03/28 23:30:52]

I think composition is still better, to hide things. Eg I deliberately didn't
expose stop in java, so only native code can explicitly stop it.

I'm sure there are arguments for others :p

+        return mThread.getLooper();
+    }
+
+    public void maybeStart() {
+        if (mStarted) return;

[agrieve, 2017/03/28 19:59:32]

nit: I think you could do away with mStarted by checking:

mThread.getState() != Thread.State.NEW

[boliu, 2017/03/28 23:30:52]

Done.

         mThread.start();
+        mStarted = true;
+    }
+
+    @CalledByNative
+    private void startAndInitialize(final long nativeThread, final long nativeEvent) {
+        maybeStart();
         new Handler(mThread.getLooper()).post(new Runnable() {
             @Override
             public void run() {
@@ -43,6 +58,7 @@ class JavaHandlerThread {
     @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
     @CalledByNative
     private void stop(final long nativeThread, final long nativeEvent) {
+        assert mStarted;
         final boolean quitSafely = Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR2;
         new Handler(mThread.getLooper()).post(new Runnable() {
             @Override