Adding a server side, non-blocking subprocess mechanism.

testing/legion/client_rpc_methods.py

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Defines the client RPC methods."""
 
+import os
+import sys
 import logging
-import subprocess
 import threading
 
+#pylint: disable=relative-import
+import common_lib
+
+# Map swarming_client to use subprocess42
+sys.path.append(common_lib.SWARMING_DIR)
+
+from utils import subprocess42
+
 
 class RPCMethods(object):
   """Class exposing RPC methods."""
 
+  _dotted_whitelist = ['subprocess']
+
   def __init__(self, server):
-    self.server = server
+    self._server = server
+    self.subprocess = Subprocess
+
+  def _dispatch(self, method, params):
+    obj = self
+    if '.' in method:
+      # Allow only white listed dotted names
+      name, method = method.split('.')
+      assert name in self._dotted_whitelist
+      obj = getattr(self, name)
+    return getattr(obj, method)(*params)
 
   def Echo(self, message):
     """Simple RPC method to print and return a message."""
     logging.info('Echoing %s', message)
     return 'echo %s' % str(message)
 
-  def Subprocess(self, cmd):
-    """Run the commands in a subprocess.
-
-    Returns:
-      (returncode, stdout, stderr).
-    """
-    p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
-                         stderr=subprocess.PIPE)
-    stdout, stderr = p.communicate()
-    return (p.returncode, stdout, stderr)
-
   def Quit(self):
-    """Call server.shutdown in another thread.
+    """Call _server.shutdown in another thread.
 
     This is needed because server.shutdown waits for the server to actually
     quit. However the server cannot shutdown until it completes handling this
     call. Calling this in the same thread results in a deadlock.
     """
-    t = threading.Thread(target=self.server.shutdown)
+    t = threading.Thread(target=self._server.shutdown)
     t.start()
+
+
+class Subprocess(object):
+  """Implements a server-based non-blocking subprocess.
+
+  This non-blocking subprocess allows the caller to continue operating while
+  also able to interact with this subprocess based on a key returned to
+  the caller at the time of creation.
+  """
+
+  _processes = {}
+  _process_count = 0
+  _creation_lock = threading.Lock()
+
+  def __init__(self, cmd):
+    self.proc = subprocess42.Popen(cmd, stdout=subprocess42.PIPE,
+                                   stderr=subprocess42.PIPE)
+    self.stdout = ''
+    self.stderr = ''
+    threading.Thread(target=self._run).start()
+
+  def _run(self):
+    self.stdout, self.stderr = self.proc.communicate()
+
+  @classmethod
+  def Popen(cls, cmd):
+    with cls._creation_lock:
+      key = 'Process%d' % cls._process_count

[M-A Ruel, 2015/02/12 22:05:25]

The name _process_count is a bit misleading, since you do not reduce its value
in Delete(). It's more like process_next_id.

[Mike Meade, 2015/02/12 22:12:47]

Done.

+      cls._process_count += 1
+    logging.debug('Creating process %s', key)
+    process = cls(cmd)
+    cls._processes[key] = process
+    return key
+
+  @classmethod
+  def Terminate(cls, key):
+    logging.debug('Terminating and deleting process %s', key)
+    return cls._processes.pop(key).proc.terminate()
+
+  @classmethod
+  def Kill(cls, key):
+    logging.debug('Killing and deleting process %s', key)
+    return cls._processes.pop(key).proc.kill()
+
+  @classmethod
+  def Delete(cls, key):
+    logging.debug('Deleting process %s', key)
+    cls._processes.pop(key)
+
+  @classmethod
+  def GetReturncode(cls, key):
+    return cls._processes[key].proc.returncode
+
+  @classmethod
+  def GetStdout(cls, key):
+    return cls._processes[key].stdout
+
+  @classmethod
+  def GetStderr(cls, key):
+    return cls._processes[key].stderr
+
+  @classmethod
+  def Wait(cls, key):
+    return cls._processes[key].proc.wait()
+
+  @classmethod
+  def Poll(cls, key):
+    return cls._processes[key].proc.poll()
+
+  @classmethod
+  def GetPid(cls, key):
+    return cls._processes[key].proc.pid