Flush more often in gclient's SubprocessCallAndFilter....

gclient_utils.py

 # Copyright 2009 Google Inc.  All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 261 matching lines @@
     print('\n________ running \'%s\' in \'%s\''
           % (' '.join(command), in_directory))
 
   # *Sigh*:  Windows needs shell=True, or else it won't search %PATH% for the
   # executable, but shell=True makes subprocess on Linux fail when it's called
   # with a list because it only tries to execute the first item in the list.
   kid = subprocess.Popen(command, bufsize=0, cwd=in_directory,
       shell=(sys.platform == 'win32'), stdout=subprocess.PIPE,
       stderr=subprocess.STDOUT)
 
+  # Do a flush of sys.stdout before we begin reading from the subprocess's
+  # stdout.
+  last_flushed_at = time.time()
+  sys.stdout.flush()
+
   # Also, we need to forward stdout to prevent weird re-ordering of output.
   # This has to be done on a per byte basis to make sure it is not buffered:
   # normally buffering is done for each line, but if svn requests input, no
   # end-of-line character is output after the prompt and it would not show up.
   in_byte = kid.stdout.read(1)
   in_line = ''
   while in_byte:
     if in_byte != '\r':
       if print_stdout:
         if not print_messages:
           print('\n________ running \'%s\' in \'%s\''
               % (' '.join(command), in_directory))
           print_messages = True
         sys.stdout.write(in_byte)
       if in_byte != '\n':
         in_line += in_byte
-    if in_byte == '\n' and filter_fn:
-      filter_fn(in_line)
+    if in_byte == '\n':
+      if filter_fn:
+        filter_fn(in_line)
       in_line = ''
+      # Flush at least 10 seconds between line writes.  We wait at least 10
+      # seconds to avoid overloading the reader that called us with output,
+      # which can slow busy readers down.
+      if (time.time() - last_flushed_at) > 10:
+        last_flushed_at = time.time()
+        sys.stdout.flush()
     in_byte = kid.stdout.read(1)
   rv = kid.wait()
 
   if rv:
     msg = 'failed to run command: %s' % ' '.join(command)
 
     if fail_status != None:
       print >>sys.stderr, msg
       sys.exit(fail_status)
 
@@ skipping 152 matching lines @@
       self.lock.acquire()
       assert not d.name in self.ran
       if not d.name in self.ran:
         self.ran.append(d.name)
       self.running.remove(d)
       if self.progress:
         self.progress.update(1)
     finally:
       self.lock.release()
     return True