Android: Disallow multiple launcher activities

[Ebola16]

Fixes https://bugs.dolphin-emu.org/issues/11935

[sepalani]

Isn't there a cleaner way to know if the activity's launching/running rather than adding another static?

[Ebola16]

@Tilka (I think you were flacs from IRC) After the IRC discussion, I looked at the code again. I think launch() and launchfile() are actually called from the same thread. Those methods eventually trigger EmulationFragment.runWithValidSurface(), which is where concurrent threads are made. At least I'm pretty sure that's what's going on here, still shaky with thread safety.

@sepalani I looked into a few options to see if I could detect if the NativeEmulation thread is already running. Thread.isAlive() was a possibility but I've read a few reports saying that it's unreliable during thread startup. Other options were more complicated than necessary from what I've read. The static boolean seems to work.

[sepalani]

It turns out that from what I read, the boolean variable is the only/simplest method so far to prevent an event from firing twice. Even disabling the element won't work as multiple events can be in the queue and will be handled before disabling it.

[Ebola16]

@sepalani Good to hear we found the same thing on using a boolean here. Is the new variable naming scheme acceptable now?

[sepalani]

@Ebola16 The naming is better, IMO. You just need to rename finishedLaunchingEmulation to something more fitting.

The other alternative I found regarding this issue is using a lock (mutex) but I'm not well versed in Android to know if it's the Android-way of handling this.

[Ebola16]

@sepalani Hopefully the latest version of this PR solves the naming problems. I tried a lock object (like the one in #8833) but ended up getting an ANR since I was making the UI thread wait.