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>

1 files changed, 151 insertions, 131 deletions

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