Refactor nag functionality in to NagTimer class.

subprocess2.py

Index: subprocess2.py
diff --git a/subprocess2.py b/subprocess2.py
index e81798613cf6946789841df1dd4fce44417d9897..f5363db197c250c1b1d1a08d806ee9dfc7b6abaa 100644
--- a/subprocess2.py
+++ b/subprocess2.py
@@ -132,6 +132,42 @@ def get_english_env(env):
   return env
 
 
+class NagTimer(object):
+  """
+  Triggers a callback when a time interval passes without an event being fired.
+
+  For example, the event could be receiving terminal output from a subprocess;
+  and the callback could print a warning to stderr that the subprocess appeared
+  to be hung.
+  """
+  def __init__(self, interval, cb):
+    self.interval = interval
+    self.cb = cb
+    self.timer = threading.Timer(self.interval, self.fn)
+    self.last_output = self.previous_last_output = 0
+
+  def start(self):
+    self.last_output = self.previous_last_output = time.time()
+    self.timer.start()
+
+  def event(self):
+    self.last_output = time.time()
+
+  def fn(self):
+    now = time.time()
+    if self.last_output == self.previous_last_output:
+      self.cb(now - self.previous_last_output)
+    # Use 0.1 fudge factor, just in case
+    #   (self.last_output - now) is very close to zero.
+    sleep_time = (self.last_output - now - 0.1) % self.interval

[M-A Ruel, 2013/05/03 16:42:58]

% with float? You should use an explicit cast in that case and also in
self.internal = int(interval)

[szager1, 2013/05/03 18:16:58]

Can you explain why?  I can't think of a good reason to forbid floats here.  The
float type in python fully supports __mod__.

[M-A Ruel, 2013/05/03 18:32:34]

Ah ok I hadn't realized that.

+    self.previous_last_output = self.last_output
+    self.timer = threading.Timer(sleep_time + 0.1, self.fn)
+    self.timer.start()
+
+  def cancel(self):
+    self.timer.cancel()
+
+
 class Popen(subprocess.Popen):
   """Wraps subprocess.Popen() with various workarounds.
 
@@ -230,8 +266,7 @@ class Popen(subprocess.Popen):
     # because of memory exhaustion.
     queue = Queue.Queue()
     done = threading.Event()
-    timer = []
-    last_output = [time.time()] * 2
+    nag = None
 
     def write_stdin():
       try:
@@ -253,28 +288,12 @@ class Popen(subprocess.Popen):
           data = pipe.read(1)
           if not data:
             break
-          last_output[0] = time.time()
+          if nag:
+            nag.event()
           queue.put((name, data))
       finally:
         queue.put(name)
 
-    def nag_fn():
-      now = time.time()
-      if done.is_set():
-        return
-      if last_output[0] == last_output[1]:
-        logging.warn('  No output for %.0f seconds from command:' % (
-            now - last_output[1]))
-        logging.warn('    %s' % self.cmd_str)
-      # Use 0.1 fudge factor in case:
-      #   now ~= last_output[0] + self.nag_timer
-      sleep_time = self.nag_timer + last_output[0] - now - 0.1
-      while sleep_time < 0:
-        sleep_time += self.nag_timer
-      last_output[1] = last_output[0]
-      timer[0] = threading.Timer(sleep_time, nag_fn)
-      timer[0].start()
-
     def timeout_fn():
       try:
         done.wait(self.timeout)
@@ -313,8 +332,11 @@ class Popen(subprocess.Popen):
       t.start()
 
     if self.nag_timer:
-      timer.append(threading.Timer(self.nag_timer, nag_fn))
-      timer[0].start()
+      def _nag_cb(elapsed):
+        logging.warn('  No output for %.0f seconds from command:' % elapsed)
+        logging.warn('    %s' % self.cmd_str)
+      nag = NagTimer(self.nag_timer, _nag_cb)
+      nag.start()
 
     timed_out = False
     try:
@@ -339,8 +361,8 @@ class Popen(subprocess.Popen):
     finally:
       # Stop the threads.
       done.set()
-      if timer:
-        timer[0].cancel()
+      if nag:
+        nag.cancel()
       if 'wait' in threads:
         # Accelerate things, otherwise it would hang until the child process is
         # done.