Multiprocess support

[beeender]

This PR will test the possibility of current status of multi process first. Then maybe add more features to make multi process work better.

Fixes #1091

• Core bug Shared_WaitForChange occasionally gets itself into an indefinite hang (30+ minutes) realm-core#887 needs to be fixed
• Permission control
• Compact Realm when there is an opened Realm in other process
• Delete
• Share Realm in the app directory with another apk
• Example two processes in one apk
• Example two processes in two apks
• Consider the following implementation with fine grained notification.
• Blog post.
• Decouple Android only logic from BaseRealm (Optional)
• Handle schema changes

[beeender]

Right now, merging this PR means more virtual spaces are needed for the shared group in RealmDaemon. Need realm/realm-core#838 to be implemented first.

[nhachicha]

s/ore/or

[Zhuinden]

Native Wait for change method is notified by changes in other process? 😮

[Zhuinden]

I guess the question is when multiprocess will be supported for migrations / schema changes / lock version change.

[cmelchior]

@Zhuinden In theory with the things we have merged to master, interprocess should be fully supported now, but we still need to review it with that in mind. At least last we checked there was a few unfortunate race conditions when opening Realms, e.g opening a Realm for the first time in a process requires a write transaction and if another process is writing at the same time, you suddenly completely blocked one of the processes.

Which is why we are not officially saying it is "done" yet 😄

[simc]

@cmelchior Is there any news on this issue? I still need multiprocess support :/

[Elvis10ten]

Hello, Is multi process now supported in realm 3 ?. I also have a question here about multi-process: http://stackoverflow.com/questions/42733931/realm-multi-process-best-practice

[Zhuinden]

This PR is like, super-outdated 😄 there is no such thing as HandlerController!

[beeender]

Replaced by #5473