Synchronize Reader Search adapter

[malinajirka]

Fixes #9987

This fix is more of a shot in the dark. We have been seeing this ChangeObserver is already registered. exception for the last couple of years and we haven't been able to find steps how to reproduce it.

I gathered recent crashes

• https://sentry.io/organizations/a8c/issues/1098765930/events/4eb41d6c962e4071a4a3fe11e4f884d4/
• https://sentry.io/organizations/a8c/issues/1101891157/?query=is%3Aunresolved%20IllegalStateException
• https://sentry.io/organizations/a8c/issues/1096892978/?query=is%3Aunresolved%20IllegalStateException
• https://sentry.io/organizations/a8c/issues/1098698974/?query=is%3Aunresolved%20IllegalStateException
  And one reoccurring Track event is "reader_search_loaded". I believe this is the line on which the app is crashing

  WordPress-Android/WordPress/src/main/java/org/wordpress/android/ui/reader/adapters/ReaderSearchSuggestionAdapter.java

  Line 71 in ac56c49

  swapCursor(matrixCursor);

  .

I wasn't able to find any other reasonable explanation what is causing the issue other than multiple threads are trying to update the cursor or mCurrentFilter at the same time. I decided to synchronize the methods which are changing mCurrentFilter or the Cursor. I believe it can't hurt us and there is a chance it might fix the issue.

To test:

1. Open Reader
2. Search some queries -> eg. "a", "an", "and", "andr" ...
3. Type "a" and notice all the previous searches "a", "an", "and", "andr" are suggested to you
4. Type "android" and make sure the search works as expected.

Update release notes:

• The change is too minor

[mkevins]

This looks like a good approach to me. I didn't do an exhaustive search through the code paths of these methods. Do you know whether the calls will generally be non-blocking? I'm trying to rule out chances for dead-lock (but haven't diagrammed the control flow graph). If it's more-or-less linear, I think this is definitely the way to go. 👍

[malinajirka]

Thanks @mkevins!

I'm trying to rule out chances for dead-lock

I think there is only one resource so I believe it's dead-lock free.

[mkevins]

I think there is only one resource so I believe it's dead-lock free.

Sounds good then. Nice work @malinajirka 🎉