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/selftest/cases/runqemu.py

@@ -163,12 +163,11 @@ class QemuTest(OESelftestTestCase):
         bitbake(cls.recipe)
 
     def _start_qemu_shutdown_check_if_shutdown_succeeded(self, qemu, timeout):
+        # Allow the runner's LoggingThread instance to exit without errors
+        # (such as the exception "Console connection closed unexpectedly")
+        # as qemu will disappear when we shut it down
+        qemu.runner.allowexit()
         qemu.run_serial("shutdown -h now")
-        # Stop thread will stop the LoggingThread instance used for logging
-        # qemu through serial console, stop thread will prevent this code
-        # from facing exception (Console connection closed unexpectedly)
-        # when qemu was shutdown by the above shutdown command
-        qemu.runner.stop_thread()
         time_track = 0
         try:
             while True:

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