commit 07e317c3cd9fe38954813b75ac582dd64f0c41f1
author Mitchell Wills <mwills@google.com> Thu Aug 11 11:05:03 2016 -0700
committer Mitchell Wills <mwills@google.com> Mon Aug 29 11:26:53 2016 -0700
tree 2fa854ae3f9190c8464ebbc65e7a994290251c9f
parent 18af49395c18ce58f76cb137ec6981bd615d5719

Add Log.wtf when transitionTo is used improperly

Using transitionTo in exit/enter (except in the terminal state) is
documented as undefined behavior and may cause unexpected results.
The current implementation appears to finish the current transition and
then transition to the new target state.

TEST=flash and play with the phone, no sign of immediate WTFs

Change-Id: I38a34b85c43d53c51514339587fc1269a069a454
(cherry picked from commit 8d3ed21583a8d83047cee1735cf669e131809e73)

core/java/com/android/internal/util/StateMachine.java

diff --git a/core/java/com/android/internal/util/StateMachine.java b/core/java/com/android/internal/util/StateMachine.java
index f137821..b0d45e1d1 100644
--- a/core/java/com/android/internal/util/StateMachine.java
+++ b/core/java/com/android/internal/util/StateMachine.java
@@ -750,6 +750,14 @@
         /** The destination state when transitionTo has been invoked */
         private State mDestState;
 
+        /**
+         * Indicates if a transition is in progress
+         *
+         * This will be true for all calls of State.exit and all calls of State.enter except for the
+         * last enter call for the current destination state.
+         */
+        private boolean mTransitionInProgress = false;
+
         /** The list of deferred messages */
         private ArrayList<Message> mDeferredMessages = new ArrayList<Message>();
 
@@ -862,6 +870,8 @@
                      * invoke the exit methods then the enter methods.
                      */
                     StateInfo commonStateInfo = setupTempStateStackWithStatesToEnter(destState);
+                    // flag is cleared in invokeEnterMethods before entering the target state
+                    mTransitionInProgress = true;
                     invokeExitMethods(commonStateInfo);
                     int stateStackEnteringIndex = moveTempStateStackToStateStack();
                     invokeEnterMethods(stateStackEnteringIndex);
@@ -1017,10 +1027,15 @@
          */
         private final void invokeEnterMethods(int stateStackEnteringIndex) {
             for (int i = stateStackEnteringIndex; i <= mStateStackTopIndex; i++) {
+                if (stateStackEnteringIndex == mStateStackTopIndex) {
+                    // Last enter state for transition
+                    mTransitionInProgress = false;
+                }
                 if (mDbg) mSm.log("invokeEnterMethods: " + mStateStack[i].state.getName());
                 mStateStack[i].state.enter();
                 mStateStack[i].active = true;
             }
+            mTransitionInProgress = false; // ensure flag set to false if no methods called
         }
 
         /**
@@ -1196,6 +1211,10 @@
 
         /** @see StateMachine#transitionTo(IState) */
         private final void transitionTo(IState destState) {
+            if (mTransitionInProgress) {
+                Log.wtf(mSm.mName, "transitionTo called while transition already in progress to " +
+                        mDestState + ", new target state=" + destState);
+            }
             mDestState = (State) destState;
             if (mDbg) mSm.log("transitionTo: destState=" + mDestState.getName());
         }