Android EGL: Synchronize calls to eglSwapBuffers and eglMakeCurrent

webrtc/api/java/android/org/webrtc/EglBase.java

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 package org.webrtc;
 
 import android.graphics.SurfaceTexture;
 import android.view.Surface;
 
 import javax.microedition.khronos.egl.EGL10;
 
 
 /**
  * Holds EGL state and utility methods for handling an egl 1.0 EGLContext, an EGLDisplay,
  * and an EGLSurface.
  */
 public abstract class EglBase {
   // EGL wrapper for an actual EGLContext.
   public static class Context {
   }
 
+  // According to the documentation, EGL can be used from multiple threads at the same time if each
+  // thread has its own EGLContext, but in practice it deadlocks on some devices when doing this.
+  // Therefore, synchronize on this global lock before calling dangerous EGL functions that might
+  // deadlock. See https://bugs.chromium.org/p/webrtc/issues/detail?id=5702 for more info.
+  public static final Object lock = new Object();
+
   // These constants are taken from EGL14.EGL_OPENGL_ES2_BIT and EGL14.EGL_CONTEXT_CLIENT_VERSION.
   // https://android.googlesource.com/platform/frameworks/base/+/master/opengl/java/android/opengl/EGL14.java
   // This is similar to how GlSurfaceView does:
   // http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/opengl/GLSurfaceView.java#760
   private static final int EGL_OPENGL_ES2_BIT = 4;
   // Android-specific extension.
   private static final int EGL_RECORDABLE_ANDROID = 0x3142;
 
   public static final int[] CONFIG_PLAIN = {
     EGL10.EGL_RED_SIZE, 8,
@@ skipping 75 matching lines @@
 
   public abstract void release();
 
   public abstract void makeCurrent();
 
   // Detach the current EGL context, so that it can be made current on another thread.
   public abstract void detachCurrent();
 
   public abstract void swapBuffers();
 }