oeqa/qemurunner: Improve logging thread exit handling for qemu shutdown test

Rather than totally disabling the logging, inform it we're about to exit
so we can log messages over the exit cleanly too. This aids debugging. It
also avoids a race where the logging handler could still error whilst
shutting down.

Also remove a race window by notificing the handler of the shutdown
first, before triggering it. This removes a race window I watched in
local testing.

(From OE-Core rev: 0e19f31a1005f94105e1cef252abfffcef2aafad)

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

meta/lib/oeqa/utils/qemurunner.py

@@ -534,6 +534,10 @@ class QemuRunner:
             self.thread.stop()
             self.thread.join()
 
+    def allowexit(self):
+        if self.thread:
+            self.thread.allowexit()
+
     def restart(self, qemuparams = None):
         self.logger.warning("Restarting qemu process")
         if self.runqemu.poll() is None:
@@ -630,6 +634,7 @@ class LoggingThread(threading.Thread):
         self.logger = logger
         self.readsock = None
         self.running = False
+        self.canexit = False
 
         self.errorevents = select.POLLERR | select.POLLHUP | select.POLLNVAL
         self.readevents = select.POLLIN | select.POLLPRI
@@ -663,6 +668,9 @@ class LoggingThread(threading.Thread):
         self.close_ignore_error(self.writepipe)
         self.running = False
 
+    def allowexit(self):
+        self.canexit = True
+
     def eventloop(self):
         poll = select.poll()
         event_read_mask = self.errorevents | self.readevents
@@ -719,7 +727,9 @@ class LoggingThread(threading.Thread):
             # happened. But for this code it counts as an
             # error since the connection shouldn't go away
             # until qemu exits.
-            raise Exception("Console connection closed unexpectedly")
+            if not self.canexit:
+                raise Exception("Console connection closed unexpectedly")
+            return ''
 
         return data