Bug 1384062 - Make SystemResourceMonitor.stop more resilient to errors. r=ahal,gps a=IanN DONTBUILD CLOSED TREE SEAMONKEY_2_49_ESR_RELBRANCH
authorMike Hommey <mh+mozilla@glandium.org>
Wed, 16 Aug 2017 13:16:16 +0900
changeset 357558 3c7797e7a8ddd3b7ddebcfe400828787e041d161
parent 357557 65825fac321f21f865e50b7c09aaa968c040d2c4
child 357559 a7d832fb13d102d77690756bf5e26b046ffacf78
push id7836
push userfrgrahl@gmx.net
push dateMon, 15 Jul 2019 16:17:02 +0000
treeherdermozilla-esr52@3a4afe7ecac5 [default view] [failures only]
perfherder[talos] [build metrics] [platform microbench] (compared to previous push)
reviewersahal, gps, IanN
bugs1384062, 1239939, 1272782
Bug 1384062 - Make SystemResourceMonitor.stop more resilient to errors. r=ahal,gps a=IanN DONTBUILD CLOSED TREE SeaMonkey ESR52 release branch only. The poll() call in SystemResourceMonitor.stop might fail even though there is something to read from the pipe, in some corner cases, and python won't let us know about it. In that case, an exception is thrown, leaving the SystemResourceMonitor (and its callers) in a weird state. In practice, this leads BuildMonitor.__exit__ to recall stop, which then fails. So when poll() throws an exception, we pretend there's still something to read, and we try to read anyways. If there is something to read, recv() will return it, otherwise, it will throw an exception of its own, which we catch, pretending we're done. Furthermore, when there is nothing to read from the pipe, poll() simply returns False, and our loop never sets `done` to True, and we then hit an assert, which doesn't have its place here, so we remove it. Finally, the other end of the pipe might have died at any time, making sending over the pipe fail, so we also protect against that. With all these changes, it feels like the reason to backout bug 1239939 in bug 1272782 should have been dealt with, and we can drop the timeout again.
--- a/testing/mozbase/mozsystemmonitor/mozsystemmonitor/resourcemonitor.py
+++ b/testing/mozbase/mozsystemmonitor/mozsystemmonitor/resourcemonitor.py
@@ -284,57 +284,71 @@ class SystemResourceMonitor(object):
         if not self._process:
             self._stopped = True
         assert self._running
         assert not self._stopped
-        self._pipe.send(('terminate',))
+        try:
+            self._pipe.send(('terminate',))
+        except Exception:
+            pass
         self._running = False
         self._stopped = True
         self.measurements = []
-        done = False
         # The child process will send each data sample over the pipe
         # as a separate data structure. When it has finished sending
         # samples, it sends a special "done" message to indicate it
         # is finished.
-        while self._pipe.poll(1.0):
-            start_time, end_time, io_diff, cpu_diff, cpu_percent, virt_mem, \
-                swap_mem = self._pipe.recv()
+        # multiprocessing.Pipe is not actually a pipe on at least Linux.  that
+        # has an effect on the expected outcome of reading from it when the
+        # other end of the pipe dies, leading to possibly hanging on revc()
+        # below. So we must poll().
+        def poll():
+            try:
+                return self._pipe.poll(0.1)
+            except Exception:
+                # Poll might throw an exception even though there's still
+                # data to read. That happens when the underlying system call
+                # returns both POLLERR and POLLIN, but python doesn't tell us
+                # about it. So assume there is something to read, and we'll
+                # get an exception when trying to read the data.
+                return True
+        while poll():
+            try:
+                start_time, end_time, io_diff, cpu_diff, cpu_percent, virt_mem, \
+                    swap_mem = self._pipe.recv()
+            except Exception:
+                # Let's assume we're done here
+                break
             # There should be nothing after the "done" message so
             # terminate.
             if start_time == 'done':
-                done = True
             io = self._io_type(*io_diff)
             virt = self._virt_type(*virt_mem)
             swap = self._swap_type(*swap_mem)
             cpu_times = [self._cpu_times_type(*v) for v in cpu_diff]
             self.measurements.append(SystemResourceUsage(start_time, end_time,
                                                          cpu_times, cpu_percent, io, virt, swap))
         # We establish a timeout so we don't hang forever if the child
         # process has crashed.
         if self._process.is_alive():
-        else:
-            # We should have received a "done" message from the
-            # child indicating it shut down properly. This only
-            # happens if the child shuts down cleanly.
-            assert done
         if len(self.measurements):
             self.start_time = self.measurements[0].start
             self.end_time = self.measurements[-1].end
     # Methods to record events alongside the monitored data.
     def record_event(self, name):