ssh: rewrite proxy management for multiprocessing usagev2.15

We changed sync to use multiprocessing for parallel work.  This broke
the ssh proxy code as it's all based on threads.  Rewrite the logic to
be multiprocessing safe.

Now instead of the module acting as a stateful object, callers have to
instantiate a new ProxyManager class that holds all the state, an pass
that down to any users.

Bug: https://crbug.com/gerrit/12389
Change-Id: I4b1af116f7306b91e825d3c56fb4274c9b033562
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/305486
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Chris Mcdonald <cjmcdonald@google.com>

6 files changed, 225 insertions, 158 deletions

diff --git a/git_command.py b/git_command.py
index fabad0e0..04953f38 100644
--- a/git_command.py
+++ b/git_command.py
@@ -21,7 +21,6 @@ from error import GitError
 from git_refs import HEAD
 import platform_utils
 from repo_trace import REPO_TRACE, IsTrace, Trace
-import ssh
 from wrapper import Wrapper
 
 GIT = 'git'
@@ -167,7 +166,7 @@ class GitCommand(object):
                capture_stderr=False,
                merge_output=False,
                disable_editor=False,
-               ssh_proxy=False,
+               ssh_proxy=None,
                cwd=None,
                gitdir=None):
     env = self._GetBasicEnv()
@@ -175,8 +174,8 @@ class GitCommand(object):
     if disable_editor:
       env['GIT_EDITOR'] = ':'
     if ssh_proxy:
-      env['REPO_SSH_SOCK'] = ssh.sock()
-      env['GIT_SSH'] = ssh.proxy()
+      env['REPO_SSH_SOCK'] = ssh_proxy.sock()
+      env['GIT_SSH'] = ssh_proxy.proxy
       env['GIT_SSH_VARIANT'] = 'ssh'
     if 'http_proxy' in env and 'darwin' == sys.platform:
       s = "'http.proxy=%s'" % (env['http_proxy'],)
@@ -259,7 +258,7 @@ class GitCommand(object):
       raise GitError('%s: %s' % (command[1], e))
 
     if ssh_proxy:
-      ssh.add_client(p)
+      ssh_proxy.add_client(p)
 
     self.process = p
     if input:
@@ -271,7 +270,8 @@ class GitCommand(object):
     try:
       self.stdout, self.stderr = p.communicate()
     finally:
-      ssh.remove_client(p)
+      if ssh_proxy:
+        ssh_proxy.remove_client(p)
     self.rc = p.wait()
 
   @staticmethod
diff --git a/git_config.py b/git_config.py
index d7fef8ca..978f6a59 100644
--- a/git_config.py
+++ b/git_config.py
@@ -27,7 +27,6 @@ import urllib.request
 from error import GitError, UploadError
 import platform_utils
 from repo_trace import Trace
-import ssh
 from git_command import GitCommand
 from git_refs import R_CHANGES, R_HEADS, R_TAGS
 
@@ -519,17 +518,23 @@ class Remote(object):
 
     return self.url.replace(longest, longestUrl, 1)
 
-  def PreConnectFetch(self):
+  def PreConnectFetch(self, ssh_proxy):
     """Run any setup for this remote before we connect to it.
 
     In practice, if the remote is using SSH, we'll attempt to create a new
     SSH master session to it for reuse across projects.
 
+    Args:
+      ssh_proxy: The SSH settings for managing master sessions.
+
     Returns:
       Whether the preconnect phase for this remote was successful.
     """
+    if not ssh_proxy:
+      return True
+
     connectionUrl = self._InsteadOf()
-    return ssh.preconnect(connectionUrl)
+    return ssh_proxy.preconnect(connectionUrl)
 
   def ReviewUrl(self, userEmail, validate_certs):
     if self._review_url is None:
diff --git a/project.py b/project.py
index 37558061..2f83d796 100644
--- a/project.py
+++ b/project.py
@@ -2045,8 +2045,8 @@ class Project(object):
       name = self.remote.name
 
     remote = self.GetRemote(name)
-    if not remote.PreConnectFetch():
-      ssh_proxy = False
+    if not remote.PreConnectFetch(ssh_proxy):
+      ssh_proxy = None
 
     if initial:
       if alt_dir and 'objects' == os.path.basename(alt_dir):
diff --git a/ssh.py b/ssh.py
index d06c4eb2..0ae8d120 100644
--- a/ssh.py
+++ b/ssh.py
@@ -15,25 +15,20 @@
 """Common SSH management logic."""
 
 import functools
+import multiprocessing
 import os
 import re
 import signal
 import subprocess
 import sys
 import tempfile
-try:
-  import threading as _threading
-except ImportError:
-  import dummy_threading as _threading
 import time
 
 import platform_utils
 from repo_trace import Trace
 
 
-_ssh_proxy_path = None
-_ssh_sock_path = None
-_ssh_clients = []
+PROXY_PATH = os.path.join(os.path.dirname(__file__), 'git_ssh')
 
 
 def _run_ssh_version():
@@ -62,68 +57,104 @@ def version():
     sys.exit(1)
 
 
-def proxy():
-  global _ssh_proxy_path
-  if _ssh_proxy_path is None:
-    _ssh_proxy_path = os.path.join(
-        os.path.dirname(__file__),
-        'git_ssh')
-  return _ssh_proxy_path
+URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
+URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
 
 
-def add_client(p):
-  _ssh_clients.append(p)
+class ProxyManager:
+  """Manage various ssh clients & masters that we spawn.
 
+  This will take care of sharing state between multiprocessing children, and
+  make sure that if we crash, we don't leak any of the ssh sessions.
 
-def remove_client(p):
-  try:
-    _ssh_clients.remove(p)
-  except ValueError:
-    pass
-
+  The code should work with a single-process scenario too, and not add too much
+  overhead due to the manager.
+  """
 
-def _terminate_clients():
-  global _ssh_clients
-  for p in _ssh_clients:
+  # Path to the ssh program to run which will pass our master settings along.
+  # Set here more as a convenience API.
+  proxy = PROXY_PATH
+
+  def __init__(self, manager):
+    # Protect access to the list of active masters.
+    self._lock = multiprocessing.Lock()
+    # List of active masters (pid).  These will be spawned on demand, and we are
+    # responsible for shutting them all down at the end.
+    self._masters = manager.list()
+    # Set of active masters indexed by "host:port" information.
+    # The value isn't used, but multiprocessing doesn't provide a set class.
+    self._master_keys = manager.dict()
+    # Whether ssh masters are known to be broken, so we give up entirely.
+    self._master_broken = manager.Value('b', False)
+    # List of active ssh sesssions.  Clients will be added & removed as
+    # connections finish, so this list is just for safety & cleanup if we crash.
+    self._clients = manager.list()
+    # Path to directory for holding master sockets.
+    self._sock_path = None
+
+  def __enter__(self):
+    """Enter a new context."""
+    return self
+
+  def __exit__(self, exc_type, exc_value, traceback):
+    """Exit a context & clean up all resources."""
+    self.close()
+
+  def add_client(self, proc):
+    """Track a new ssh session."""
+    self._clients.append(proc.pid)
+
+  def remove_client(self, proc):
+    """Remove a completed ssh session."""
     try:
-      os.kill(p.pid, signal.SIGTERM)
-      p.wait()
-    except OSError:
+      self._clients.remove(proc.pid)
+    except ValueError:
       pass
-  _ssh_clients = []
-
-
-_master_processes = []
-_master_keys = set()
-_ssh_master = True
-_master_keys_lock = None
-
-
-def init():
-  """Should be called once at the start of repo to init ssh master handling.
-
-  At the moment, all we do is to create our lock.
-  """
-  global _master_keys_lock
-  assert _master_keys_lock is None, "Should only call init once"
-  _master_keys_lock = _threading.Lock()
-
-
-def _open_ssh(host, port=None):
-  global _ssh_master
-
-  # Bail before grabbing the lock if we already know that we aren't going to
-  # try creating new masters below.
-  if sys.platform in ('win32', 'cygwin'):
-    return False
-
-  # Acquire the lock.  This is needed to prevent opening multiple masters for
-  # the same host when we're running "repo sync -jN" (for N > 1) _and_ the
-  # manifest <remote fetch="ssh://xyz"> specifies a different host from the
-  # one that was passed to repo init.
-  _master_keys_lock.acquire()
-  try:
 
+  def add_master(self, proc):
+    """Track a new master connection."""
+    self._masters.append(proc.pid)
+
+  def _terminate(self, procs):
+    """Kill all |procs|."""
+    for pid in procs:
+      try:
+        os.kill(pid, signal.SIGTERM)
+        os.waitpid(pid, 0)
+      except OSError:
+        pass
+
+    # The multiprocessing.list() API doesn't provide many standard list()
+    # methods, so we have to manually clear the list.
+    while True:
+      try:
+        procs.pop(0)
+      except:
+        break
+
+  def close(self):
+    """Close this active ssh session.
+
+    Kill all ssh clients & masters we created, and nuke the socket dir.
+    """
+    self._terminate(self._clients)
+    self._terminate(self._masters)
+
+    d = self.sock(create=False)
+    if d:
+      try:
+        platform_utils.rmdir(os.path.dirname(d))
+      except OSError:
+        pass
+
+  def _open_unlocked(self, host, port=None):
+    """Make sure a ssh master session exists for |host| & |port|.
+
+    If one doesn't exist already, we'll create it.
+
+    We won't grab any locks, so the caller has to do that.  This helps keep the
+    business logic of actually creating the master separate from grabbing locks.
+    """
     # Check to see whether we already think that the master is running; if we
     # think it's already running, return right away.
     if port is not None:
@@ -131,17 +162,15 @@ def _open_ssh(host, port=None):
     else:
       key = host
 
-    if key in _master_keys:
+    if key in self._master_keys:
       return True
 
-    if not _ssh_master or 'GIT_SSH' in os.environ:
+    if self._master_broken.value or 'GIT_SSH' in os.environ:
       # Failed earlier, so don't retry.
       return False
 
     # We will make two calls to ssh; this is the common part of both calls.
-    command_base = ['ssh',
-                    '-o', 'ControlPath %s' % sock(),
-                    host]
+    command_base = ['ssh', '-o', 'ControlPath %s' % self.sock(), host]
     if port is not None:
       command_base[1:1] = ['-p', str(port)]
 
@@ -161,7 +190,7 @@ def _open_ssh(host, port=None):
       if not isnt_running:
         # Our double-check found that the master _was_ infact running.  Add to
         # the list of keys.
-        _master_keys.add(key)
+        self._master_keys[key] = True
         return True
     except Exception:
       # Ignore excpetions.  We we will fall back to the normal command and print
@@ -173,7 +202,7 @@ def _open_ssh(host, port=None):
       Trace(': %s', ' '.join(command))
       p = subprocess.Popen(command)
     except Exception as e:
-      _ssh_master = False
+      self._master_broken.value = True
       print('\nwarn: cannot enable ssh control master for %s:%s\n%s'
             % (host, port, str(e)), file=sys.stderr)
       return False
@@ -183,75 +212,66 @@ def _open_ssh(host, port=None):
     if ssh_died:
       return False
 
-    _master_processes.append(p)
-    _master_keys.add(key)
+    self.add_master(p)
+    self._master_keys[key] = True
     return True
-  finally:
-    _master_keys_lock.release()
 
+  def _open(self, host, port=None):
+    """Make sure a ssh master session exists for |host| & |port|.
 
-def close():
-  global _master_keys_lock
-
-  _terminate_clients()
-
-  for p in _master_processes:
-    try:
-      os.kill(p.pid, signal.SIGTERM)
-      p.wait()
-    except OSError:
-      pass
-  del _master_processes[:]
-  _master_keys.clear()
-
-  d = sock(create=False)
-  if d:
-    try:
-      platform_utils.rmdir(os.path.dirname(d))
-    except OSError:
-      pass
-
-  # We're done with the lock, so we can delete it.
-  _master_keys_lock = None
+    If one doesn't exist already, we'll create it.
 
+    This will obtain any necessary locks to avoid inter-process races.
+    """
+    # Bail before grabbing the lock if we already know that we aren't going to
+    # try creating new masters below.
+    if sys.platform in ('win32', 'cygwin'):
+      return False
 
-URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
-URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
+    # Acquire the lock.  This is needed to prevent opening multiple masters for
+    # the same host when we're running "repo sync -jN" (for N > 1) _and_ the
+    # manifest <remote fetch="ssh://xyz"> specifies a different host from the
+    # one that was passed to repo init.
+    with self._lock:
+      return self._open_unlocked(host, port)
+
+  def preconnect(self, url):
+    """If |uri| will create a ssh connection, setup the ssh master for it."""
+    m = URI_ALL.match(url)
+    if m:
+      scheme = m.group(1)
+      host = m.group(2)
+      if ':' in host:
+        host, port = host.split(':')
+      else:
+        port = None
+      if scheme in ('ssh', 'git+ssh', 'ssh+git'):
+        return self._open(host, port)
+      return False
 
+    m = URI_SCP.match(url)
+    if m:
+      host = m.group(1)
+      return self._open(host)
 
-def preconnect(url):
-  m = URI_ALL.match(url)
-  if m:
-    scheme = m.group(1)
-    host = m.group(2)
-    if ':' in host:
-      host, port = host.split(':')
-    else:
-      port = None
-    if scheme in ('ssh', 'git+ssh', 'ssh+git'):
-      return _open_ssh(host, port)
     return False
 
-  m = URI_SCP.match(url)
-  if m:
-    host = m.group(1)
-    return _open_ssh(host)
-
-  return False
-
-def sock(create=True):
-  global _ssh_sock_path
-  if _ssh_sock_path is None:
-    if not create:
-      return None
-    tmp_dir = '/tmp'
-    if not os.path.exists(tmp_dir):
-      tmp_dir = tempfile.gettempdir()
-    if version() < (6, 7):
-      tokens = '%r@%h:%p'
-    else:
-      tokens = '%C'  # hash of %l%h%p%r
-    _ssh_sock_path = os.path.join(
-        tempfile.mkdtemp('', 'ssh-', tmp_dir),
-        'master-' + tokens)
-  return _ssh_sock_path
+  def sock(self, create=True):
+    """Return the path to the ssh socket dir.
+
+    This has all the master sockets so clients can talk to them.
+    """
+    if self._sock_path is None:
+      if not create:
+        return None
+      tmp_dir = '/tmp'
+      if not os.path.exists(tmp_dir):
+        tmp_dir = tempfile.gettempdir()
+      if version() < (6, 7):
+        tokens = '%r@%h:%p'
+      else:
+        tokens = '%C'  # hash of %l%h%p%r
+      self._sock_path = os.path.join(
+          tempfile.mkdtemp('', 'ssh-', tmp_dir),
+          'master-' + tokens)
+    return self._sock_path
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 28568062..fb25c221 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -358,7 +358,7 @@ later is required to fix a server side protocol bug.
           optimized_fetch=opt.optimized_fetch,
           retry_fetches=opt.retry_fetches,
           prune=opt.prune,
-          ssh_proxy=True,
+          ssh_proxy=self.ssh_proxy,
           clone_filter=self.manifest.CloneFilter,
           partial_clone_exclude=self.manifest.PartialCloneExclude)
 
@@ -380,7 +380,11 @@ later is required to fix a server side protocol bug.
     finish = time.time()
     return (success, project, start, finish)
 
-  def _Fetch(self, projects, opt, err_event):
+  @classmethod
+  def _FetchInitChild(cls, ssh_proxy):
+    cls.ssh_proxy = ssh_proxy
+
+  def _Fetch(self, projects, opt, err_event, ssh_proxy):
     ret = True
 
     jobs = opt.jobs_network if opt.jobs_network else self.jobs
@@ -410,8 +414,14 @@ later is required to fix a server side protocol bug.
           break
       return ret
 
+    # We pass the ssh proxy settings via the class.  This allows multiprocessing
+    # to pickle it up when spawning children.  We can't pass it as an argument
+    # to _FetchProjectList below as multiprocessing is unable to pickle those.
+    Sync.ssh_proxy = None
+
     # NB: Multiprocessing is heavy, so don't spin it up for one job.
     if len(projects_list) == 1 or jobs == 1:
+      self._FetchInitChild(ssh_proxy)
       if not _ProcessResults(self._FetchProjectList(opt, x) for x in projects_list):
         ret = False
     else:
@@ -429,7 +439,8 @@ later is required to fix a server side protocol bug.
       else:
         pm.update(inc=0, msg='warming up')
         chunksize = 4
-      with multiprocessing.Pool(jobs) as pool:
+      with multiprocessing.Pool(
+          jobs, initializer=self._FetchInitChild, initargs=(ssh_proxy,)) as pool:
         results = pool.imap_unordered(
             functools.partial(self._FetchProjectList, opt),
             projects_list,
@@ -438,6 +449,11 @@ later is required to fix a server side protocol bug.
           ret = False
           pool.close()
 
+    # Cleanup the reference now that we're done with it, and we're going to
+    # release any resources it points to.  If we don't, later multiprocessing
+    # usage (e.g. checkouts) will try to pickle and then crash.
+    del Sync.ssh_proxy
+
     pm.end()
     self._fetch_times.Save()
 
@@ -447,7 +463,7 @@ later is required to fix a server side protocol bug.
     return (ret, fetched)
 
   def _FetchMain(self, opt, args, all_projects, err_event, manifest_name,
-                 load_local_manifests):
+                 load_local_manifests, ssh_proxy):
     """The main network fetch loop.
 
     Args:
@@ -457,6 +473,7 @@ later is required to fix a server side protocol bug.
       err_event: Whether an error was hit while processing.
       manifest_name: Manifest file to be reloaded.
       load_local_manifests: Whether to load local manifests.
+      ssh_proxy: SSH manager for clients & masters.
     """
     rp = self.manifest.repoProject
 
@@ -467,7 +484,7 @@ later is required to fix a server side protocol bug.
     to_fetch.extend(all_projects)
     to_fetch.sort(key=self._fetch_times.Get, reverse=True)
 
-    success, fetched = self._Fetch(to_fetch, opt, err_event)
+    success, fetched = self._Fetch(to_fetch, opt, err_event, ssh_proxy)
     if not success:
       err_event.set()
 
@@ -498,7 +515,7 @@ later is required to fix a server side protocol bug.
       if previously_missing_set == missing_set:
         break
       previously_missing_set = missing_set
-      success, new_fetched = self._Fetch(missing, opt, err_event)
+      success, new_fetched = self._Fetch(missing, opt, err_event, ssh_proxy)
       if not success:
         err_event.set()
       fetched.update(new_fetched)
@@ -985,12 +1002,15 @@ later is required to fix a server side protocol bug.
 
     self._fetch_times = _FetchTimes(self.manifest)
     if not opt.local_only:
-      try:
-        ssh.init()
-        self._FetchMain(opt, args, all_projects, err_event, manifest_name,
-                        load_local_manifests)
-      finally:
-        ssh.close()
+      with multiprocessing.Manager() as manager:
+        with ssh.ProxyManager(manager) as ssh_proxy:
+          # Initialize the socket dir once in the parent.
+          ssh_proxy.sock()
+          self._FetchMain(opt, args, all_projects, err_event, manifest_name,
+                          load_local_manifests, ssh_proxy)
+
+      if opt.network_only:
+        return
 
       # If we saw an error, exit with code 1 so that other scripts can check.
       if err_event.is_set():
diff --git a/tests/test_ssh.py b/tests/test_ssh.py
index 5a4f27e4..ffb5cb94 100644
--- a/tests/test_ssh.py
+++ b/tests/test_ssh.py
@@ -14,6 +14,8 @@
 
 """Unittests for the ssh.py module."""
 
+import multiprocessing
+import subprocess
 import unittest
 from unittest import mock
 
@@ -39,14 +41,34 @@ class SshTests(unittest.TestCase):
     with mock.patch('ssh._run_ssh_version', return_value='OpenSSH_1.2\n'):
       self.assertEqual(ssh.version(), (1, 2))
 
+  def test_context_manager_empty(self):
+    """Verify context manager with no clients works correctly."""
+    with multiprocessing.Manager() as manager:
+      with ssh.ProxyManager(manager):
+        pass
+
+  def test_context_manager_child_cleanup(self):
+    """Verify orphaned clients & masters get cleaned up."""
+    with multiprocessing.Manager() as manager:
+      with ssh.ProxyManager(manager) as ssh_proxy:
+        client = subprocess.Popen(['sleep', '964853320'])
+        ssh_proxy.add_client(client)
+        master = subprocess.Popen(['sleep', '964853321'])
+        ssh_proxy.add_master(master)
+    # If the process still exists, these will throw timeout errors.
+    client.wait(0)
+    master.wait(0)
+
   def test_ssh_sock(self):
     """Check sock() function."""
+    manager = multiprocessing.Manager()
+    proxy = ssh.ProxyManager(manager)
     with mock.patch('tempfile.mkdtemp', return_value='/tmp/foo'):
       # old ssh version uses port
       with mock.patch('ssh.version', return_value=(6, 6)):
-        self.assertTrue(ssh.sock().endswith('%p'))
-      ssh._ssh_sock_path = None
+        self.assertTrue(proxy.sock().endswith('%p'))
+
+      proxy._sock_path = None
       # new ssh version uses hash
       with mock.patch('ssh.version', return_value=(6, 7)):
-        self.assertTrue(ssh.sock().endswith('%C'))
-      ssh._ssh_sock_path = None
+        self.assertTrue(proxy.sock().endswith('%C'))