[Devil] Add timeout to logcat record thread join.

devil/devil/android/logcat_monitor.py

Index: devil/devil/android/logcat_monitor.py
diff --git a/devil/devil/android/logcat_monitor.py b/devil/devil/android/logcat_monitor.py
index 497a6bf92c097286b7b49493defe4e031019acd3..a3d51e8f33e13f2f05009d9e93b4f072eda648a2 100644
--- a/devil/devil/android/logcat_monitor.py
+++ b/devil/devil/android/logcat_monitor.py
@@ -20,6 +20,7 @@ from devil.utils import reraiser_thread
 
 class LogcatMonitor(object):
 
+  _LOGCAT_GENERATOR_TIMEOUT = 5.0
   _WAIT_TIME = 0.2
   _THREADTIME_RE_FORMAT = (
       r'(?P<date>\S*) +(?P<time>\S*) +(?P<proc_id>%s) +(?P<thread_id>%s) +'
@@ -154,13 +155,23 @@ class LogcatMonitor(object):
     def record_to_file():
       # Write the log with line buffering so the consumer sees each individual
       # line.
+      logcat_generator = self._adb.Logcat(filter_specs=self._filter_specs,
+                                          logcat_format='threadtime')
+      @decorators.WithExplicitTimeoutAndRetries(

[jbudorick, 2016/01/26 23:13:19]

This decorator is here to check a condition (whether the timeout has been hit)
and kill the function's execution if that condition is met. In this case, it
does so s.t. it can check another condition -- whether
self._stop_recording_event is set -- and kill the loop if that condition is met.

Why don't we skip the timeout portion and just have the supervising thread kill
the generator thread if the event is set?

[jbudorick, 2016/01/26 23:32:37]

As for the slowness part, we could potentially add something to reraiser_thread
s.t. we could run a generator in one thread and iterate over it in another. I
think that could keep us from creating another thread on each logcat line.

+          self._LOGCAT_GENERATOR_TIMEOUT, 0)
+      def logcat_next():
+        logcat_generator.next()
+
       with open(self._record_file.name, 'a', 1) as f:
-        for data in self._adb.Logcat(filter_specs=self._filter_specs,
-                                     logcat_format='threadtime'):
+        while True:
+          try:
+            data = logcat_next()
+            f.write(data + '\n')
+          except device_errors.CommandTimeoutError:
+            pass
           if self._stop_recording_event.isSet():
             f.flush()
             return
-          f.write(data + '\n')
 
     self._stop_recording_event.clear()
     if not self._record_thread: