bitbake: server/process: Run idle commands in a separate idle thread

When bitbake is off running heavier "idle" commands, it doesn't service it's
command socket which means stopping/interrupting it is hard. It also means we
can't "ping" from the UI to know if it is still alive.

For those reasons, split idle command execution into it's own thread.

The commands are generally already self containted so this is easier than
expected. We do have to be careful to only handle inotify poll() from a single
thread at a time. It also means we always have to use a thread lock when sending
events since both the idle thread and the command thread may generate log messages
(and hence events). The patch depends on  previous fixes to the builtins locking
in event.py and the heartbeat enable/disable changes as well as other locking
additions.

We use a condition to signal from the idle thread when other sections of code
can continue, thanks to Joshua Watt for the review and tweaks squashed into this
patch. We do have some sync points where we need to ensure any currently executing
commands have finished before we can start a new async command for example.

(Bitbake rev: 67dd9a5e84811df8869a82da6a37a41ee8fe94e2)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/xmlrpcserver.py

@@ -118,7 +118,7 @@ class BitBakeXMLRPCServerCommands():
         """
         Run a cooker command on the server
         """
-        return self.server.cooker.command.runCommand(command, self.server.readonly)
+        return self.server.cooker.command.runCommand(command, self.server, self.server.readonly)
 
     def getEventHandle(self):
         return self.event_handle