Dialog internal.

Dialog internally holds a PhoneWindow, which is the same as an Activity's root view hierarchy.

    Dialog(@NonNull Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
...
        mWindowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

        final Window w = new PhoneWindow(mContext);
        mWindow = w;
        w.setCallback(this);
        w.setOnWindowDismissedCallback(this);
        w.setWindowManager(mWindowManager, null, null);
        w.setGravity(Gravity.CENTER);

        mListenersHandler = new ListenersHandler(this);
    }

Here is an short doc for the token in WindowManager.LayoutParams, this is for later reference. in another word, the token for LayoutParams is the token for the ActivityRecord this can be deduced from ActivityThread.destroyAcitivty

       /**
         * The general type of window.  There are three main classes of
         * window types:
         * <ul>
         * <li> <strong>Application windows</strong> (ranging from
         * {@link #FIRST_APPLICATION_WINDOW} to
         * {@link #LAST_APPLICATION_WINDOW}) are normal top-level application
         * windows.  For these types of windows, the {@link #token} must be
         * set to the token of the activity they are a part of (this will
         * normally be done for you if {@link #token} is null).
         * <li> <strong>Sub-windows</strong> (ranging from
         * {@link #FIRST_SUB_WINDOW} to
         * {@link #LAST_SUB_WINDOW}) are associated with another top-level
         * window.  For these types of windows, the {@link #token} must be
         * the token of the window it is attached to.
         * <li> <strong>System windows</strong> (ranging from
         * {@link #FIRST_SYSTEM_WINDOW} to
         * {@link #LAST_SYSTEM_WINDOW}) are special types of windows for
         * use by the system for specific purposes.  They should not normally
         * be used by applications, and a special permission is required
         * to use them.
         * </ul>

When the Dialog is going to be shown, its DecorView will be added into WMS, and so the ViewRootImpl and LayoutParam are created for this special window, however, the LayoutParam share the same token as ActivityRecord

Dialog will be dismissed in the case of calling dismiss(), this can be done safely from UI thread, or another thread with Looper installed.

    public void dismiss() {
        if (Looper.myLooper() == mHandler.getLooper()) {
            dismissDialog();
        } else {
            mHandler.post(mDismissAction);
        }
    }

in both case, dismissDialog will get called, it will try to remove the mDecor from window manager immediately

    void dismissDialog() {
        if (mDecor == null || !mShowing) {
            return;
        }

        if (mWindow.isDestroyed()) {
            Log.e(TAG, "Tried to dismissDialog() but the Dialog's window was already destroyed!");
            return;
        }

        try {
            mWindowManager.removeViewImmediate(mDecor);
        } finally {
            if (mActionMode != null) {
                mActionMode.finish();
            }
            mDecor = null;
            mWindow.closeAllPanels();
            onStop();
            mShowing = false;

            sendDismissMessage();
        }
    }

The real handler for mWindowManager is WindowManagerGlobal

    public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }

Here is where you may see the poplular Exception thrown by findViewLocked, ironically, the Exception is not captured/handled.

The exception

java.lang.IllegalArgumentException: View not attached to window manager
    at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:356)
    at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:201)
    at android.view.Window$LocalWindowManager.removeView(Window.java:400)
    at android.app.Dialog.dismissDialog(Dialog.java:268)
    at android.app.Dialog.access$000(Dialog.java:69)
    at android.app.Dialog$1.run(Dialog.java:103)
    at android.app.Dialog.dismiss(Dialog.java:252)
    at xxx.onPostExecute(xxx$1.java:xxx)

The location cause the exception is:

    private int findViewLocked(View view, boolean required) {
        final int index = mViews.indexOf(view);
        if (required && index < 0) {
            throw new IllegalArgumentException("View=" + view + " not attached to window manager");
        }
        return index;
    }

Why the index can be negative ?, i.e. no such DecorView exists ?

This is because corresponding View RootViewImpl LayoutParam are moved away from WMS in a different path, by triggering handleDestroyActivity, either destroy or relaunch the activity.

    private void handleDestroyActivity(IBinder token, boolean finishing,
            int configChanges, boolean getNonConfigInstance) {
            ...
                WindowManagerGlobal.getInstance().closeAll(token,
                        r.activity.getClass().getName(), "Activity");
            ...
    }

WindowManagerGlobal will handle it like

    private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }

later on the mDiyViews will be destroyed, if all this happenef before you trying to dismiss the dialog manually, the findViewLocked will return -1, and crash.