From 7bd4a2750253a2049a5ad0cff171eb4f6beb57ff Mon Sep 17 00:00:00 2001
From: "fischman@webrtc.org"
 <fischman@webrtc.org@4adac7df-926f-26a2-2b94-8c16560cd09d>
Date: Tue, 4 Mar 2014 18:17:55 +0000
Subject: [PATCH] VideoCaptureAndroid: don't deliver frames after
 stopCapture().

Because stopCapture() and onPreviewFrame() are called on different threads, and
are both synchronized, it's possible for onPreviewFrame() to commence execution
after stopCapture() has completed, causing a SEGV because the native code is no
longer prepared to accept frames.
Clarify the contract around synchronized methods in this class to hopefully
avoid similar bugs in future.

BUG=2947
R=henrike@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9339004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5639 4adac7df-926f-26a2-2b94-8c16560cd09d
---
 .../videoengine/VideoCaptureAndroid.java      | 26 +++++++++++++------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/webrtc/modules/video_capture/android/java/src/org/webrtc/videoengine/VideoCaptureAndroid.java b/webrtc/modules/video_capture/android/java/src/org/webrtc/videoengine/VideoCaptureAndroid.java
index 691531f873..dfe63adfe6 100644
--- a/webrtc/modules/video_capture/android/java/src/org/webrtc/videoengine/VideoCaptureAndroid.java
+++ b/webrtc/modules/video_capture/android/java/src/org/webrtc/videoengine/VideoCaptureAndroid.java
@@ -31,7 +31,9 @@ import android.view.SurfaceHolder.Callback;
 // the entry points to this class are all synchronized.  This shouldn't present
 // a performance bottleneck because only onPreviewFrame() is called more than
 // once (and is called serially on a single thread), so the lock should be
-// uncontended.
+// uncontended.  Note that each of these synchronized methods must check
+// |camera| for null to account for having possibly waited for stopCapture() to
+// complete.
 public class VideoCaptureAndroid implements PreviewCallback, Callback {
   private final static String TAG = "WEBRTC-JC";
 
@@ -149,7 +151,13 @@ public class VideoCaptureAndroid implements PreviewCallback, Callback {
   private native void ProvideCameraFrame(
       byte[] data, int length, long captureObject);
 
-  public synchronized void onPreviewFrame(byte[] data, Camera camera) {
+  public synchronized void onPreviewFrame(byte[] data, Camera callbackCamera) {
+    if (camera == null) {
+      return;
+    }
+    if (camera != callbackCamera) {
+      throw new RuntimeException("Unexpected camera in callback!");
+    }
     ProvideCameraFrame(data, data.length, native_capturer);
     camera.addCallbackBuffer(data);
   }
@@ -184,10 +192,11 @@ public class VideoCaptureAndroid implements PreviewCallback, Callback {
 
   public synchronized void surfaceCreated(SurfaceHolder holder) {
     Log.d(TAG, "VideoCaptureAndroid::surfaceCreated");
+    if (camera == null) {
+      return;
+    }
     try {
-      if (camera != null) {
-        camera.setPreviewDisplay(holder);
-      }
+      camera.setPreviewDisplay(holder);
     } catch (IOException e) {
       throw new RuntimeException(e);
     }
@@ -195,10 +204,11 @@ public class VideoCaptureAndroid implements PreviewCallback, Callback {
 
   public synchronized void surfaceDestroyed(SurfaceHolder holder) {
     Log.d(TAG, "VideoCaptureAndroid::surfaceDestroyed");
+    if (camera == null) {
+      return;
+    }
     try {
-      if (camera != null) {
-        camera.setPreviewDisplay(null);
-      }
+      camera.setPreviewDisplay(null);
     } catch (IOException e) {
       throw new RuntimeException(e);
     }