Introduce write lock for mDragState (7a5d007a) · Commits · e / os / android_frameworks_base

services/core/java/com/android/server/wm/DragDropController.java

+214 −165

Original line number	Diff line number	Diff line
		@@ -52,6 +52,8 @@ class DragDropController {

		/**
		* Drag state per operation.
		* Needs a lock of {@code WindowManagerService#mWindowMap} to read this. Needs both locks of
		* {@code mWriteLock} and {@code WindowManagerService#mWindowMap} to update this.
		* The variable is cleared by {@code #onDragStateClosedLocked} which is invoked by DragState
		* itself, thus the variable can be null after calling DragState's methods.
		*/
		@@ -59,6 +61,38 @@ class DragDropController {

		private WindowManagerService mService;
		private final Handler mHandler;
		/**
		* Lock to preserve the order of state updates.
		* The lock is used to process drag and drop state updates in order without having the window
		* manager lock.
		*
		* Suppose DragDropController invokes a callback method A, then processes the following update
		* A'. Same for a callback method B and the following update B'. The callback wants
		* DragDropController to processes the updates in the order of A' then B'.
		*
		* Without mWriteLock: the following race can happen.
		*
		* 1. Thread a calls A.
		* 2. Thread b calls B.
		* 3. Thread b acquires the window manager lock
		* 4. thread b processes the update B'
		* 5. Thread a acquires the window manager lock
		* 6. thread a processes the update A'
		*
		* With mWriteLock we can ensure the order of A' and B'
		*
		* 1. Thread a acquire mWriteLock
		* 2. Thread a calls A
		* 3. Thread a acquire the window manager lock
		* 4. Thread a processes A'
		* 5. Thread b acquire mWriteLock
		* 6. Thread b calls B
		* 7. Thread b acquire the window manager lock
		* 8. Thread b processes B'
		*
		* Don't acquire the lock while holding the window manager lock, otherwise it causes a deadlock.
		*/
		private final Object mWriteLock = new Object();

		boolean dragDropActiveLocked() {
		return mDragState != null;
		@@ -85,8 +119,7 @@ class DragDropController {
		+ " asbinder=" + window.asBinder());
		}

		IBinder token = null;

		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (dragDropActiveLocked()) {
		Slog.w(TAG_WM, "Drag already in progress");
		@@ -110,10 +143,11 @@ class DragDropController {
		}
		surface.setAlpha(alpha);

		if (SHOW_TRANSACTIONS) Slog.i(TAG_WM, " DRAG " + surface + ": CREATE");
		if (SHOW_TRANSACTIONS)
		Slog.i(TAG_WM, " DRAG " + surface + ": CREATE");
		outSurface.copyFrom(surface);
		final IBinder winBinder = window.asBinder();
		token = new Binder();
		IBinder token = new Binder();
		mDragState = new DragState(mService, token, surface, flags, winBinder);
		mDragState.mPid = callerPid;
		mDragState.mUid = callerUid;
		@@ -122,10 +156,10 @@ class DragDropController {

		// 5 second timeout for this window to actually begin the drag
		sendTimeoutMessage(MSG_DRAG_START_TIMEOUT, winBinder);
		}

		return token;
		}
		}
		}

		boolean performDrag(IWindow window, IBinder dragToken,
		int touchSource, float touchX, float touchY, float thumbCenterX, float thumbCenterY,
		@@ -134,6 +168,7 @@ class DragDropController {
		Slog.d(TAG_WM, "perform drag: win=" + window + " data=" + data);
		}

		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (mDragState == null) {
		Slog.w(TAG_WM, "No drag prepared");
		@@ -187,8 +222,7 @@ class DragDropController {

		// Make the surface visible at the proper location
		final SurfaceControl surfaceControl = mDragState.mSurfaceControl;
		if (SHOW_LIGHT_TRANSACTIONS) Slog.i(
		TAG_WM, ">>> OPEN TRANSACTION performDrag");
		if (SHOW_LIGHT_TRANSACTIONS) Slog.i(TAG_WM, ">>> OPEN TRANSACTION performDrag");
		mService.openSurfaceTransaction();
		try {
		surfaceControl.setPosition(touchX - thumbCenterX,
		@@ -198,12 +232,14 @@ class DragDropController {
		surfaceControl.show();
		} finally {
		mService.closeSurfaceTransaction("performDrag");
		if (SHOW_LIGHT_TRANSACTIONS) Slog.i(
		TAG_WM, "<<< CLOSE TRANSACTION performDrag");
		if (SHOW_LIGHT_TRANSACTIONS) {
		Slog.i(TAG_WM, "<<< CLOSE TRANSACTION performDrag");
		}
		}

		mDragState.notifyLocationLocked(touchX, touchY);
		}
		}

		return true; // success!
		}
		@@ -214,6 +250,7 @@ class DragDropController {
		Slog.d(TAG_WM, "Drop result=" + consumed + " reported by " + token);
		}

		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (mDragState == null) {
		// Most likely the drop recipient ANRed and we ended the drag
		@@ -238,16 +275,19 @@ class DragDropController {
		return; // !!! TODO: throw here?
		}


		mDragState.mDragResult = consumed;
		mDragState.endDragLocked();
		}
		}
		}

		void cancelDragAndDrop(IBinder dragToken) {
		if (DEBUG_DRAG) {
		Slog.d(TAG_WM, "cancelDragAndDrop");
		}

		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (mDragState == null) {
		Slog.w(TAG_WM, "cancelDragAndDrop() without prepareDrag()");
		@@ -265,6 +305,7 @@ class DragDropController {
		mDragState.cancelDragLocked();
		}
		}
		}

		/**
		* Handles motion events.
		@@ -274,6 +315,7 @@ class DragDropController {
		* @param newY Y coordinate value in dp in the screen coordinate
		*/
		void handleMotionEvent(boolean keepHandling, float newX, float newY) {
		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (!dragDropActiveLocked()) {
		// The drag has ended but the clean-up message has not been processed by
		@@ -289,6 +331,7 @@ class DragDropController {
		}
		}
		}
		}

		void dragRecipientEntered(IWindow window) {
		if (DEBUG_DRAG) {
		@@ -348,20 +391,23 @@ class DragDropController {
		if (DEBUG_DRAG) {
		Slog.w(TAG_WM, "Timeout starting drag by win " + win);
		}
		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		// !!! TODO: ANR the app that has failed to start the drag in time
		if (mDragState != null) {
		mDragState.closeLocked();
		}
		}
		}
		break;
		}

		case MSG_DRAG_END_TIMEOUT: {
		IBinder win = (IBinder) msg.obj;
		final IBinder win = (IBinder) msg.obj;
		if (DEBUG_DRAG) {
		Slog.w(TAG_WM, "Timeout ending drag to win " + win);
		}
		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		// !!! TODO: ANR the drag-receiving app
		if (mDragState != null) {
		@@ -369,22 +415,24 @@ class DragDropController {
		mDragState.endDragLocked();
		}
		}
		}
		break;
		}

		case MSG_TEAR_DOWN_DRAG_AND_DROP_INPUT: {
		if (DEBUG_DRAG)
		Slog.d(TAG_WM, "Drag ending; tearing down input channel");
		DragState.InputInterceptor interceptor = (DragState.InputInterceptor) msg.obj;
		if (interceptor != null) {
		final DragState.InputInterceptor interceptor =
		(DragState.InputInterceptor) msg.obj;
		if (interceptor == null) return;
		synchronized (mService.mWindowMap) {
		interceptor.tearDown();
		}
		}
		break;
		}

		case MSG_ANIMATION_END: {
		synchronized (mWriteLock) {
		synchronized (mService.mWindowMap) {
		if (mDragState == null) {
		Slog.wtf(TAG_WM, "mDragState unexpectedly became null while " +
		@@ -393,6 +441,7 @@ class DragDropController {
		}
		mDragState.closeLocked();
		}
		}
		break;
		}
		}