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//frameworks/base/core/java/android/view/Surface.java
public class Surface implements Parcelable {
    public Canvas lockCanvas(Rect inOutDirty)
            throws Surface.OutOfResourcesException, IllegalArgumentException {
        synchronized (mLock) {
            checkNotReleasedLocked();
            if (mLockedObject != 0) {
                // Ideally, nativeLockCanvas() would throw in this situation and prevent the
                // double-lock, but that won't happen if mNativeObject was updated.  We can't
                // abandon the old mLockedObject because it might still be in use, so instead
                // we just refuse to re-lock the Surface.
                throw new IllegalArgumentException("Surface was already locked");
            }
            mLockedObject = nativeLockCanvas(mNativeObject, mCanvas, inOutDirty);
            return mCanvas;
        }
    }
}

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//frameworks/base/core/java/android/view/Surface.java
public class Surface implements Parcelable {
    public void unlockCanvasAndPost(Canvas canvas) {
        synchronized (mLock) {
            checkNotReleasedLocked();
 
 
            if (mHwuiContext != null) {
                mHwuiContext.unlockAndPost(canvas);
            } else {
                unlockSwCanvasAndPost(canvas);
            }
        }
    }
}