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
-
-
-def _terminate_clients():
-  global _ssh_clients
-  for p in _ssh_clients:
-    try:
-      os.kill(p.pid, signal.SIGTERM)
-      p.wait()
-    except OSError:
-      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.
+  The code should work with a single-process scenario too, and not add too much
+  overhead due to the manager.
   """
-  global _master_keys_lock
-  assert _master_keys_lock is None, "Should only call init once"
-  _master_keys_lock = _threading.Lock()
 
+  # 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 _open_ssh(host, port=None):
-  global _ssh_master
+  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
 
-  # 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
+  def __enter__(self):
+    """Enter a new context."""
+    return self
 
-  # 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 __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:
+      self._clients.remove(proc.pid)
+    except ValueError:
+      pass
+
+  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
+    If one doesn't exist already, we'll create it.
 
-  _terminate_clients()
+    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
 
-  for p in _master_processes:
-    try:
-      os.kill(p.pid, signal.SIGTERM)
-      p.wait()
-    except OSError:
-      pass
-  del _master_processes[:]
-  _master_keys.clear()
+    # 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)
 
-  d = sock(create=False)
-  if d:
-    try:
-      platform_utils.rmdir(os.path.dirname(d))
-    except OSError:
-      pass
+  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
 
-  # We're done with the lock, so we can delete it.
-  _master_keys_lock = None
+    m = URI_SCP.match(url)
+    if m:
+      host = m.group(1)
+      return self._open(host)
 
-
-URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
-URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
-
-
-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)
+  def sock(self, create=True):
+    """Return the path to the ssh socket dir.
 
-  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
+    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'))