Use threads to process target function

This patch takes advantages of threads to make privsep daemon process
concurrently.

Change-Id: Ib20b27d5ea07bd0af61891c7d8c0d352a393aa21

oslo_privsep/daemon.py

@@ -43,6 +43,7 @@ The privsep daemon exits when the communication channel is closed,
 
 '''
 
+from concurrent import futures
 import enum
 import errno
 import io
@@ -64,6 +65,7 @@ import eventlet
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_utils import importutils
+import six
 
 from oslo_privsep._i18n import _
 from oslo_privsep import capabilities
@@ -352,6 +354,9 @@ class Daemon(object):
         self.user = context.conf.user
         self.group = context.conf.group
         self.caps = set(context.conf.capabilities)
+        self.thread_pool = futures.ThreadPoolExecutor(
+            context.conf.thread_pool_size)
+        self.communication_error = None
 
     def run(self):
         """Run request loop. Sets up environment, then calls loop()"""
@@ -413,22 +418,75 @@ class Daemon(object):
                 'inh': fmt_caps(inh),
             })
 
-    def _process_cmd(self, cmd, *args):
+    def _process_cmd(self, msgid, cmd, *args):
+        """Executes the requested command in an execution thread.
+
+        This executes a call within a thread executor and returns the results
+        of the execution.
+
+        :param msgid: The message identifier.
+        :param cmd: The `Message` type indicating the command type.
+        :param args: The function, args, and kwargs if a Message.CALL type.
+        :return: A tuple of the return status, optional call output, and
+                 optional error information.
+        """
         if cmd == Message.PING:
             return (Message.PONG.value,)
 
-        elif cmd == Message.CALL:
+        try:
+            if cmd != Message.CALL:
+                raise ProtocolError(_('Unknown privsep cmd: %s') % cmd)
+
+            # Extract the callable and arguments
             name, f_args, f_kwargs = args
             func = importutils.import_class(name)
-
             if not self.context.is_entrypoint(func):
                 msg = _('Invalid privsep function: %s not exported') % name
                 raise NameError(msg)
 
             ret = func(*f_args, **f_kwargs)
             return (Message.RET.value, ret)
+        except Exception as e:
+            LOG.debug(
+                'privsep: Exception during request[%(msgid)s]: '
+                '%(err)s', {'msgid': msgid, 'err': e}, exc_info=True)
+            cls = e.__class__
+            cls_name = '%s.%s' % (cls.__module__, cls.__name__)
+            return (Message.ERR.value, cls_name, e.args)
 
-        raise ProtocolError(_('Unknown privsep cmd: %s') % cmd)
+    def _create_done_callback(self, msgid):
+        """Creates a future callback to receive command execution results.
+
+        :param msgid: The message identifier.
+        :return: A future reply callback.
+        """
+        channel = self.channel
+
+        def _call_back(result):
+            """Future execution callback.
+
+            :param result: The `future` execution and its results.
+            """
+            try:
+                reply = result.result()
+                LOG.debug('privsep: reply[%(msgid)s]: %(reply)s',
+                          {'msgid': msgid, 'reply': reply})
+                channel.send((msgid, reply))
+            except IOError:
+                self.communication_error = sys.exc_info()
+            except Exception as e:
+                LOG.debug(
+                    'privsep: Exception during request[%(msgid)s]: '
+                    '%(err)s', {'msgid': msgid, 'err': e}, exc_info=True)
+                cls = e.__class__
+                cls_name = '%s.%s' % (cls.__module__, cls.__name__)
+                reply = (Message.ERR.value, cls_name, e.args)
+                try:
+                    channel.send((msgid, reply))
+                except IOError:
+                    self.communication_error = sys.exc_info()
+
+        return _call_back
 
     def loop(self):
         """Main body of daemon request loop"""
@@ -439,27 +497,16 @@ class Daemon(object):
         self.context.set_client_mode(False)
 
         for msgid, msg in self.channel:
-            LOG.debug('privsep: request[%(msgid)s]: %(req)s',
-                      {'msgid': msgid, 'req': msg})
-            try:
-                reply = self._process_cmd(*msg)
-            except Exception as e:
-                LOG.debug(
-                    'privsep: Exception during request[%(msgid)s]: %(err)s',
-                    {'msgid': msgid, 'err': e}, exc_info=True)
-                cls = e.__class__
-                cls_name = '%s.%s' % (cls.__module__, cls.__name__)
-                reply = (Message.ERR.value, cls_name, e.args)
-
-            try:
-                LOG.debug('privsep: reply[%(msgid)s]: %(reply)s',
-                          {'msgid': msgid, 'reply': reply})
-                self.channel.send((msgid, reply))
-            except IOError as e:
-                if e.errno == errno.EPIPE:
+            error = self.communication_error
+            if error:
+                if error[1].errno == errno.EPIPE:
                     # Write stream closed, exit loop
                     break
-                raise
+                six.reraise(error)
+
+            # Submit the command for execution
+            future = self.thread_pool.submit(self._process_cmd, msgid, *msg)
+            future.add_done_callback(self._create_done_callback(msgid))
 
         LOG.debug('Socket closed, shutting down privsep daemon')
 

oslo_privsep/priv_context.py

@@ -16,6 +16,7 @@
 import enum
 import functools
 import logging
+import multiprocessing
 import shlex
 import sys
 
@@ -48,6 +49,12 @@ OPTS = [
             type=types.List(CapNameOrInt), default=[],
             help=_('List of Linux capabilities retained by the privsep '
                    'daemon.')),
+    cfg.IntOpt('thread_pool_size',
+               min=1,
+               help=_("The number of threads available for privsep to "
+                      "concurrently run processes. Defaults to the number of "
+                      "CPU cores in the system."),
+               default=multiprocessing.cpu_count()),
     cfg.StrOpt('helper_command',
                help=_('Command to invoke to start the privsep daemon if '
                       'not using the "fork" method. '

oslo_privsep/tests/test_daemon.py

@@ -149,6 +149,7 @@ class DaemonTest(base.BaseTestCase):
         context = mock.NonCallableMock()
         context.conf.user = 42
         context.conf.group = 84
+        context.conf.thread_pool_size = 10
         context.conf.capabilities = [
             capabilities.CAP_SYS_ADMIN, capabilities.CAP_NET_ADMIN]
 

releasenotes/notes/add_thread_pool_size-a54e6f27ab019f96.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Privsep now uses multithreading to allow concurrency in executing
+    privileged commands. The number of concurrent threads defaults to the
+    available CPU cores, but can be adjusted by the new ``thread_pool_size``
+    config option.