Work around one Android bug and document another

* etc/PROBLEMS (Runtime problems specific to Android): Document
deficiency of "Android Keyboard (AOSP)."

* java/org/gnu/emacs/EmacsView.java (showOnScreenKeyboard):
Revert yesterday's change.

* java/org/gnu/emacs/EmacsWindow.java (toggleOnScreenKeyboard):
Sync with the UI thread after displaying the on-screen keyboard.

2 files changed, 23 insertions, 13 deletions

diff --git a/java/org/gnu/emacs/EmacsView.java b/java/org/gnu/emacs/EmacsView.java
index db270b796e8..244a3a02166 100644
--- a/java/org/gnu/emacs/EmacsView.java
+++ b/java/org/gnu/emacs/EmacsView.java
@@ -777,15 +777,6 @@ public final class EmacsView extends ViewGroup
 
     imManager.showSoftInput (this, 0);
     isCurrentlyTextEditor = true;
-
-    /* The OS text editing widget unconditionally reports the current
-       values of the selection to the input method after calls to
-       showSoftInput, which is redundant if inputConnection exists but
-       is now relied upon in such circumstances by the OS's default
-       input method, and must therefore be faithfully reproduced on our
-       part.  */
-    if (inputConnection != null)
-      EmacsNative.requestSelectionUpdate (window.handle);
   }
 
   public void
diff --git a/java/org/gnu/emacs/EmacsWindow.java b/java/org/gnu/emacs/EmacsWindow.java
index 483ba0dbced..5a4e04ae169 100644
--- a/java/org/gnu/emacs/EmacsWindow.java
+++ b/java/org/gnu/emacs/EmacsWindow.java
@@ -20,12 +20,16 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 package org.gnu.emacs;
 
 import java.lang.IllegalStateException;
+
 import java.util.ArrayList;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.ListIterator;
-import java.util.LinkedHashMap;
 import java.util.Map;
 
+import java.util.concurrent.Callable;
+import java.util.concurrent.FutureTask;
+
 import android.app.Activity;
 
 import android.content.ClipData;
@@ -1620,23 +1624,38 @@ public final class EmacsWindow extends EmacsHandleObject
   public void
   toggleOnScreenKeyboard (final boolean on)
   {
+    FutureTask<Void> task;
+
     /* Even though InputMethodManager functions are thread safe,
        `showOnScreenKeyboard' etc must be called from the UI thread in
        order to avoid deadlocks if the calls happen in tandem with a
        call to a synchronizing function within
        `onCreateInputConnection'.  */
 
-    EmacsService.SERVICE.runOnUiThread (new Runnable () {
+    task = new FutureTask<Void> (new Callable<Void> () {
         @Override
-        public void
-        run ()
+        public Void
+        call ()
         {
           if (on)
             view.showOnScreenKeyboard ();
           else
             view.hideOnScreenKeyboard ();
+          return null;
         }
       });
+
+    /* Block Lisp until this request to display the on-screen keyboard
+       is registered by the UI thread, or updates arising from a
+       redisplay that are reported between the two events will be liable
+       to run afoul of the IMM's cache of selection positions and never
+       reach the input method, if it is currently hidden, as input
+       methods receive outdated selection information reported during
+       the previous call to `onCreateInputConnection' when first
+       displayed.
+
+       Chances are this is a long-standing bug in the system.  */
+    EmacsService.<Void>syncRunnable (task);
   }
 
   public String