bitbake: cooker: Avoid parser deadlocks

If you make parsing fail (e.g. add something like:

X := "${@d.getVar('MCMACHINES').split()[1]}"

to meson.bbclass, then run "while true; do bitbake -g bash; done"
it will eventually hang. It appears the cancel_join_thread() call the
parsing failure triggers, breaks the results_queue badly enough that it
sits in read() indefintely (called from self.result_queue.get(timeout=0.25)).
The timeout only applies to lock aquisition, not the read call.

I've tried various other approaches such as using cancel_join_thread()
in other places but the only way things don't lock up is to avoid
cancel_join_thread() entirely for results_queue.

I do have a concern that this may adversely affect Ctrl+C handling
but equally, its broken now already and this appears to improve
things.

[YOCTO #14034]

(Bitbake rev: 0e0af15b84e07e6763300dcd092b980086b9b9c4)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cooker.py

@@ -1933,7 +1933,8 @@ class Parser(multiprocessing.Process):
             except queue.Empty:
                 pass
             else:
-                self.results.cancel_join_thread()
+                self.results.close()
+                self.results.join_thread()
                 break
 
             if pending:
@@ -1942,6 +1943,8 @@ class Parser(multiprocessing.Process):
                 try:
                     job = self.jobs.pop()
                 except IndexError:
+                    self.results.close()
+                    self.results.join_thread()
                     break
                 result = self.parse(*job)
                 # Clear the siggen cache after parsing to control memory usage, its huge
@@ -2060,8 +2063,6 @@ class CookerParser(object):
 
             bb.event.fire(event, self.cfgdata)
 
-        # Allow data left in the cancel queue to be discarded
-        self.parser_quit.cancel_join_thread()
         for process in self.processes:
             self.parser_quit.put(None)
 
@@ -2081,7 +2082,8 @@ class CookerParser(object):
                 process.join()
 
         self.parser_quit.close()
-        self.parser_quit.join_thread()
+        # Allow data left in the cancel queue to be discarded
+        self.parser_quit.cancel_join_thread()
 
         sync = threading.Thread(target=self.bb_cache.sync)
         self.syncthread = sync