[TIMOB-1776] Intermittent ConcurrentModificationException on Android

In StatusNet Mobile we've been working with a lot of event listeners, including Ti.App listeners for communication between our primary context, another context to run XML parsing in the background, and a WebView used for various data display.

Sometimes we end up with cases where things quite reliably crash the VM dumping a raw C-level stacktrace that can be worked around temporarily by shuffling when/where we do an addEventListener, but I'm also seeing more intermittent bugs where I get a Java-level backtrace like this:

W/dalvikvm( 1759): threadid=1: thread exiting with uncaught exception (group=0x4001d7f0)
E/TiUncaughtHandler( 1759): (main) [43,123166] Sending event: exception on thread: main msg:java.lang.RuntimeException: Unable to destroy activity {net.status.client.mobile/org.appcelerator.titanium.TiActivity}: java.util.ConcurrentModificationException
E/TiUncaughtHandler( 1759): java.lang.RuntimeException: Unable to destroy activity {net.status.client.mobile/org.appcelerator.titanium.TiActivity}: java.util.ConcurrentModificationException
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3655)
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3673)
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread.access$2900(ActivityThread.java:125)
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
E/TiUncaughtHandler( 1759):     at android.os.Handler.dispatchMessage(Handler.java:99)
E/TiUncaughtHandler( 1759):     at android.os.Looper.loop(Looper.java:123)
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread.main(ActivityThread.java:4627)
E/TiUncaughtHandler( 1759):     at java.lang.reflect.Method.invokeNative(Native Method)
E/TiUncaughtHandler( 1759):     at java.lang.reflect.Method.invoke(Method.java:521)
E/TiUncaughtHandler( 1759):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
E/TiUncaughtHandler( 1759):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
E/TiUncaughtHandler( 1759):     at dalvik.system.NativeStart.main(Native Method)
E/TiUncaughtHandler( 1759): Caused by: java.util.ConcurrentModificationException
E/TiUncaughtHandler( 1759):     at java.util.HashMap$HashIterator.nextEntry(HashMap.java:795)
E/TiUncaughtHandler( 1759):     at java.util.HashMap$KeyIterator.next(HashMap.java:822)
E/TiUncaughtHandler( 1759):     at org.appcelerator.titanium.TiContext.removeEventListenersFromContext(TiContext.java:468)
E/TiUncaughtHandler( 1759):     at org.appcelerator.titanium.TiProxy.removeEventListenersFromContext(TiProxy.java:242)
E/TiUncaughtHandler( 1759):     at org.appcelerator.titanium.TiApplication.removeEventListenersFromContext(TiApplication.java:275)
E/TiUncaughtHandler( 1759):     at org.appcelerator.titanium.TiContext.release(TiContext.java:879)
E/TiUncaughtHandler( 1759):     at org.appcelerator.titanium.TiActivity.onDestroy(TiActivity.java:415)
E/TiUncaughtHandler( 1759):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3642)
E/TiUncaughtHandler( 1759):     ... 11 more

It looks like there's a lot of unsynchronized access to the event listener hashmaps in TiContext; there's a few synchronized(eventListeners){...} constructs but they're not consistent, and I'm not too sure what does what.