darwin: add another preemptive gui() call when using chg

Changeset a89381e04c58 added this gui() call before background forks, and
Google's extensions do background forks on essentially every invocation for
logging purposes. The crash is reliably (though not 100%) reproducible without
this change when running `HGPLAIN=1 chg status` in one of our repos. With this
fix, I haven't been able to trigger the crash anymore.

Differential Revision: https://phab.mercurial-scm.org/D8141

mercurial/commandserver.py

@@ -1,727 +1,731 b''
 # commandserver.py - communicate with Mercurial's API over a pipe
 #
 #  Copyright Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import gc
 import os
 import random
 import signal
 import socket
 import struct
 import traceback
 
 try:
     import selectors
 
     selectors.BaseSelector
 except ImportError:
     from .thirdparty import selectors2 as selectors
 
 from .i18n import _
 from .pycompat import getattr
 from . import (
     encoding,
     error,
     loggingutil,
     pycompat,
     repocache,
     util,
     vfs as vfsmod,
 )
 from .utils import (
     cborutil,
     procutil,
 )
 
 
 class channeledoutput(object):
     """
     Write data to out in the following format:
 
     data length (unsigned int),
     data
     """
 
     def __init__(self, out, channel):
         self.out = out
         self.channel = channel
 
     @property
     def name(self):
         return b'<%c-channel>' % self.channel
 
     def write(self, data):
         if not data:
             return
         # single write() to guarantee the same atomicity as the underlying file
         self.out.write(struct.pack(b'>cI', self.channel, len(data)) + data)
         self.out.flush()
 
     def __getattr__(self, attr):
         if attr in ('isatty', 'fileno', 'tell', 'seek'):
             raise AttributeError(attr)
         return getattr(self.out, attr)
 
 
 class channeledmessage(object):
     """
     Write encoded message and metadata to out in the following format:
 
     data length (unsigned int),
     encoded message and metadata, as a flat key-value dict.
 
     Each message should have 'type' attribute. Messages of unknown type
     should be ignored.
     """
 
     # teach ui that write() can take **opts
     structured = True
 
     def __init__(self, out, channel, encodename, encodefn):
         self._cout = channeledoutput(out, channel)
         self.encoding = encodename
         self._encodefn = encodefn
 
     def write(self, data, **opts):
         opts = pycompat.byteskwargs(opts)
         if data is not None:
             opts[b'data'] = data
         self._cout.write(self._encodefn(opts))
 
     def __getattr__(self, attr):
         return getattr(self._cout, attr)
 
 
 class channeledinput(object):
     """
     Read data from in_.
 
     Requests for input are written to out in the following format:
     channel identifier - 'I' for plain input, 'L' line based (1 byte)
     how many bytes to send at most (unsigned int),
 
     The client replies with:
     data length (unsigned int), 0 meaning EOF
     data
     """
 
     maxchunksize = 4 * 1024
 
     def __init__(self, in_, out, channel):
         self.in_ = in_
         self.out = out
         self.channel = channel
 
     @property
     def name(self):
         return b'<%c-channel>' % self.channel
 
     def read(self, size=-1):
         if size < 0:
             # if we need to consume all the clients input, ask for 4k chunks
             # so the pipe doesn't fill up risking a deadlock
             size = self.maxchunksize
             s = self._read(size, self.channel)
             buf = s
             while s:
                 s = self._read(size, self.channel)
                 buf += s
 
             return buf
         else:
             return self._read(size, self.channel)
 
     def _read(self, size, channel):
         if not size:
             return b''
         assert size > 0
 
         # tell the client we need at most size bytes
         self.out.write(struct.pack(b'>cI', channel, size))
         self.out.flush()
 
         length = self.in_.read(4)
         length = struct.unpack(b'>I', length)[0]
         if not length:
             return b''
         else:
             return self.in_.read(length)
 
     def readline(self, size=-1):
         if size < 0:
             size = self.maxchunksize
             s = self._read(size, b'L')
             buf = s
             # keep asking for more until there's either no more or
             # we got a full line
             while s and s[-1] != b'\n':
                 s = self._read(size, b'L')
                 buf += s
 
             return buf
         else:
             return self._read(size, b'L')
 
     def __iter__(self):
         return self
 
     def next(self):
         l = self.readline()
         if not l:
             raise StopIteration
         return l
 
     __next__ = next
 
     def __getattr__(self, attr):
         if attr in ('isatty', 'fileno', 'tell', 'seek'):
             raise AttributeError(attr)
         return getattr(self.in_, attr)
 
 
 _messageencoders = {
     b'cbor': lambda v: b''.join(cborutil.streamencode(v)),
 }
 
 
 def _selectmessageencoder(ui):
     # experimental config: cmdserver.message-encodings
     encnames = ui.configlist(b'cmdserver', b'message-encodings')
     for n in encnames:
         f = _messageencoders.get(n)
         if f:
             return n, f
     raise error.Abort(
         b'no supported message encodings: %s' % b' '.join(encnames)
     )
 
 
 class server(object):
     """
     Listens for commands on fin, runs them and writes the output on a channel
     based stream to fout.
     """
 
     def __init__(self, ui, repo, fin, fout, prereposetups=None):
         self.cwd = encoding.getcwd()
 
         if repo:
             # the ui here is really the repo ui so take its baseui so we don't
             # end up with its local configuration
             self.ui = repo.baseui
             self.repo = repo
             self.repoui = repo.ui
         else:
             self.ui = ui
             self.repo = self.repoui = None
         self._prereposetups = prereposetups
 
         self.cdebug = channeledoutput(fout, b'd')
         self.cerr = channeledoutput(fout, b'e')
         self.cout = channeledoutput(fout, b'o')
         self.cin = channeledinput(fin, fout, b'I')
         self.cresult = channeledoutput(fout, b'r')
 
         if self.ui.config(b'cmdserver', b'log') == b'-':
             # switch log stream of server's ui to the 'd' (debug) channel
             # (don't touch repo.ui as its lifetime is longer than the server)
             self.ui = self.ui.copy()
             setuplogging(self.ui, repo=None, fp=self.cdebug)
 
         # TODO: add this to help/config.txt when stabilized
         # ``channel``
         #   Use separate channel for structured output. (Command-server only)
         self.cmsg = None
         if ui.config(b'ui', b'message-output') == b'channel':
             encname, encfn = _selectmessageencoder(ui)
             self.cmsg = channeledmessage(fout, b'm', encname, encfn)
 
         self.client = fin
 
     def cleanup(self):
         """release and restore resources taken during server session"""
 
     def _read(self, size):
         if not size:
             return b''
 
         data = self.client.read(size)
 
         # is the other end closed?
         if not data:
             raise EOFError
 
         return data
 
     def _readstr(self):
         """read a string from the channel
 
         format:
         data length (uint32), data
         """
         length = struct.unpack(b'>I', self._read(4))[0]
         if not length:
             return b''
         return self._read(length)
 
     def _readlist(self):
         """read a list of NULL separated strings from the channel"""
         s = self._readstr()
         if s:
             return s.split(b'\0')
         else:
             return []
 
     def runcommand(self):
         """ reads a list of \0 terminated arguments, executes
         and writes the return code to the result channel """
         from . import dispatch  # avoid cycle
 
         args = self._readlist()
 
         # copy the uis so changes (e.g. --config or --verbose) don't
         # persist between requests
         copiedui = self.ui.copy()
         uis = [copiedui]
         if self.repo:
             self.repo.baseui = copiedui
             # clone ui without using ui.copy because this is protected
             repoui = self.repoui.__class__(self.repoui)
             repoui.copy = copiedui.copy  # redo copy protection
             uis.append(repoui)
             self.repo.ui = self.repo.dirstate._ui = repoui
             self.repo.invalidateall()
 
         for ui in uis:
             ui.resetstate()
             # any kind of interaction must use server channels, but chg may
             # replace channels by fully functional tty files. so nontty is
             # enforced only if cin is a channel.
             if not util.safehasattr(self.cin, b'fileno'):
                 ui.setconfig(b'ui', b'nontty', b'true', b'commandserver')
 
         req = dispatch.request(
             args[:],
             copiedui,
             self.repo,
             self.cin,
             self.cout,
             self.cerr,
             self.cmsg,
             prereposetups=self._prereposetups,
         )
 
         try:
             ret = dispatch.dispatch(req) & 255
             self.cresult.write(struct.pack(b'>i', int(ret)))
         finally:
             # restore old cwd
             if b'--cwd' in args:
                 os.chdir(self.cwd)
 
     def getencoding(self):
         """ writes the current encoding to the result channel """
         self.cresult.write(encoding.encoding)
 
     def serveone(self):
         cmd = self.client.readline()[:-1]
         if cmd:
             handler = self.capabilities.get(cmd)
             if handler:
                 handler(self)
             else:
                 # clients are expected to check what commands are supported by
                 # looking at the servers capabilities
                 raise error.Abort(_(b'unknown command %s') % cmd)
 
         return cmd != b''
 
     capabilities = {b'runcommand': runcommand, b'getencoding': getencoding}
 
     def serve(self):
         hellomsg = b'capabilities: ' + b' '.join(sorted(self.capabilities))
         hellomsg += b'\n'
         hellomsg += b'encoding: ' + encoding.encoding
         hellomsg += b'\n'
         if self.cmsg:
             hellomsg += b'message-encoding: %s\n' % self.cmsg.encoding
         hellomsg += b'pid: %d' % procutil.getpid()
         if util.safehasattr(os, b'getpgid'):
             hellomsg += b'\n'
             hellomsg += b'pgid: %d' % os.getpgid(0)
 
         # write the hello msg in -one- chunk
         self.cout.write(hellomsg)
 
         try:
             while self.serveone():
                 pass
         except EOFError:
             # we'll get here if the client disconnected while we were reading
             # its request
             return 1
 
         return 0
 
 
 def setuplogging(ui, repo=None, fp=None):
     """Set up server logging facility
 
     If cmdserver.log is '-', log messages will be sent to the given fp.
     It should be the 'd' channel while a client is connected, and otherwise
     is the stderr of the server process.
     """
     # developer config: cmdserver.log
     logpath = ui.config(b'cmdserver', b'log')
     if not logpath:
         return
     # developer config: cmdserver.track-log
     tracked = set(ui.configlist(b'cmdserver', b'track-log'))
 
     if logpath == b'-' and fp:
         logger = loggingutil.fileobjectlogger(fp, tracked)
     elif logpath == b'-':
         logger = loggingutil.fileobjectlogger(ui.ferr, tracked)
     else:
         logpath = os.path.abspath(util.expandpath(logpath))
         # developer config: cmdserver.max-log-files
         maxfiles = ui.configint(b'cmdserver', b'max-log-files')
         # developer config: cmdserver.max-log-size
         maxsize = ui.configbytes(b'cmdserver', b'max-log-size')
         vfs = vfsmod.vfs(os.path.dirname(logpath))
         logger = loggingutil.filelogger(
             vfs,
             os.path.basename(logpath),
             tracked,
             maxfiles=maxfiles,
             maxsize=maxsize,
         )
 
     targetuis = {ui}
     if repo:
         targetuis.add(repo.baseui)
         targetuis.add(repo.ui)
     for u in targetuis:
         u.setlogger(b'cmdserver', logger)
 
 
 class pipeservice(object):
     def __init__(self, ui, repo, opts):
         self.ui = ui
         self.repo = repo
 
     def init(self):
         pass
 
     def run(self):
         ui = self.ui
         # redirect stdio to null device so that broken extensions or in-process
         # hooks will never cause corruption of channel protocol.
         with ui.protectedfinout() as (fin, fout):
             sv = server(ui, self.repo, fin, fout)
             try:
                 return sv.serve()
             finally:
                 sv.cleanup()
 
 
 def _initworkerprocess():
     # use a different process group from the master process, in order to:
     # 1. make the current process group no longer "orphaned" (because the
     #    parent of this process is in a different process group while
     #    remains in a same session)
     #    according to POSIX 2.2.2.52, orphaned process group will ignore
     #    terminal-generated stop signals like SIGTSTP (Ctrl+Z), which will
     #    cause trouble for things like ncurses.
     # 2. the client can use kill(-pgid, sig) to simulate terminal-generated
     #    SIGINT (Ctrl+C) and process-exit-generated SIGHUP. our child
     #    processes like ssh will be killed properly, without affecting
     #    unrelated processes.
     os.setpgid(0, 0)
     # change random state otherwise forked request handlers would have a
     # same state inherited from parent.
     random.seed()
 
 
 def _serverequest(ui, repo, conn, createcmdserver, prereposetups):
     fin = conn.makefile('rb')
     fout = conn.makefile('wb')
     sv = None
     try:
         sv = createcmdserver(repo, conn, fin, fout, prereposetups)
         try:
             sv.serve()
         # handle exceptions that may be raised by command server. most of
         # known exceptions are caught by dispatch.
         except error.Abort as inst:
             ui.error(_(b'abort: %s\n') % inst)
         except IOError as inst:
             if inst.errno != errno.EPIPE:
                 raise
         except KeyboardInterrupt:
             pass
         finally:
             sv.cleanup()
     except:  # re-raises
         # also write traceback to error channel. otherwise client cannot
         # see it because it is written to server's stderr by default.
         if sv:
             cerr = sv.cerr
         else:
             cerr = channeledoutput(fout, b'e')
         cerr.write(encoding.strtolocal(traceback.format_exc()))
         raise
     finally:
         fin.close()
         try:
             fout.close()  # implicit flush() may cause another EPIPE
         except IOError as inst:
             if inst.errno != errno.EPIPE:
                 raise
 
 
 class unixservicehandler(object):
     """Set of pluggable operations for unix-mode services
 
     Almost all methods except for createcmdserver() are called in the main
     process. You can't pass mutable resource back from createcmdserver().
     """
 
     pollinterval = None
 
     def __init__(self, ui):
         self.ui = ui
 
     def bindsocket(self, sock, address):
         util.bindunixsocket(sock, address)
         sock.listen(socket.SOMAXCONN)
         self.ui.status(_(b'listening at %s\n') % address)
         self.ui.flush()  # avoid buffering of status message
 
     def unlinksocket(self, address):
         os.unlink(address)
 
     def shouldexit(self):
         """True if server should shut down; checked per pollinterval"""
         return False
 
     def newconnection(self):
         """Called when main process notices new connection"""
 
     def createcmdserver(self, repo, conn, fin, fout, prereposetups):
         """Create new command server instance; called in the process that
         serves for the current connection"""
         return server(self.ui, repo, fin, fout, prereposetups)
 
 
 class unixforkingservice(object):
     """
     Listens on unix domain socket and forks server per connection
     """
 
     def __init__(self, ui, repo, opts, handler=None):
         self.ui = ui
         self.repo = repo
         self.address = opts[b'address']
         if not util.safehasattr(socket, b'AF_UNIX'):
             raise error.Abort(_(b'unsupported platform'))
         if not self.address:
             raise error.Abort(_(b'no socket path specified with --address'))
         self._servicehandler = handler or unixservicehandler(ui)
         self._sock = None
         self._mainipc = None
         self._workeripc = None
         self._oldsigchldhandler = None
         self._workerpids = set()  # updated by signal handler; do not iterate
         self._socketunlinked = None
         # experimental config: cmdserver.max-repo-cache
         maxlen = ui.configint(b'cmdserver', b'max-repo-cache')
         if maxlen < 0:
             raise error.Abort(_(b'negative max-repo-cache size not allowed'))
         self._repoloader = repocache.repoloader(ui, maxlen)
+        # attempt to avoid crash in CoreFoundation when using chg after fix in
+        # a89381e04c58
+        if pycompat.isdarwin:
+            procutil.gui()
 
     def init(self):
         self._sock = socket.socket(socket.AF_UNIX)
         # IPC channel from many workers to one main process; this is actually
         # a uni-directional pipe, but is backed by a DGRAM socket so each
         # message can be easily separated.
         o = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM)
         self._mainipc, self._workeripc = o
         self._servicehandler.bindsocket(self._sock, self.address)
         if util.safehasattr(procutil, b'unblocksignal'):
             procutil.unblocksignal(signal.SIGCHLD)
         o = signal.signal(signal.SIGCHLD, self._sigchldhandler)
         self._oldsigchldhandler = o
         self._socketunlinked = False
         self._repoloader.start()
 
     def _unlinksocket(self):
         if not self._socketunlinked:
             self._servicehandler.unlinksocket(self.address)
             self._socketunlinked = True
 
     def _cleanup(self):
         signal.signal(signal.SIGCHLD, self._oldsigchldhandler)
         self._sock.close()
         self._mainipc.close()
         self._workeripc.close()
         self._unlinksocket()
         self._repoloader.stop()
         # don't kill child processes as they have active clients, just wait
         self._reapworkers(0)
 
     def run(self):
         try:
             self._mainloop()
         finally:
             self._cleanup()
 
     def _mainloop(self):
         exiting = False
         h = self._servicehandler
         selector = selectors.DefaultSelector()
         selector.register(
             self._sock, selectors.EVENT_READ, self._acceptnewconnection
         )
         selector.register(
             self._mainipc, selectors.EVENT_READ, self._handlemainipc
         )
         while True:
             if not exiting and h.shouldexit():
                 # clients can no longer connect() to the domain socket, so
                 # we stop queuing new requests.
                 # for requests that are queued (connect()-ed, but haven't been
                 # accept()-ed), handle them before exit. otherwise, clients
                 # waiting for recv() will receive ECONNRESET.
                 self._unlinksocket()
                 exiting = True
             try:
                 events = selector.select(timeout=h.pollinterval)
             except OSError as inst:
                 # selectors2 raises ETIMEDOUT if timeout exceeded while
                 # handling signal interrupt. That's probably wrong, but
                 # we can easily get around it.
                 if inst.errno != errno.ETIMEDOUT:
                     raise
                 events = []
             if not events:
                 # only exit if we completed all queued requests
                 if exiting:
                     break
                 continue
             for key, _mask in events:
                 key.data(key.fileobj, selector)
         selector.close()
 
     def _acceptnewconnection(self, sock, selector):
         h = self._servicehandler
         try:
             conn, _addr = sock.accept()
         except socket.error as inst:
             if inst.args[0] == errno.EINTR:
                 return
             raise
 
         # Future improvement: On Python 3.7, maybe gc.freeze() can be used
         # to prevent COW memory from being touched by GC.
         # https://instagram-engineering.com/
         #   copy-on-write-friendly-python-garbage-collection-ad6ed5233ddf
         pid = os.fork()
         if pid:
             try:
                 self.ui.log(
                     b'cmdserver', b'forked worker process (pid=%d)\n', pid
                 )
                 self._workerpids.add(pid)
                 h.newconnection()
             finally:
                 conn.close()  # release handle in parent process
         else:
             try:
                 selector.close()
                 sock.close()
                 self._mainipc.close()
                 self._runworker(conn)
                 conn.close()
                 self._workeripc.close()
                 os._exit(0)
             except:  # never return, hence no re-raises
                 try:
                     self.ui.traceback(force=True)
                 finally:
                     os._exit(255)
 
     def _handlemainipc(self, sock, selector):
         """Process messages sent from a worker"""
         try:
             path = sock.recv(32768)  # large enough to receive path
         except socket.error as inst:
             if inst.args[0] == errno.EINTR:
                 return
             raise
         self._repoloader.load(path)
 
     def _sigchldhandler(self, signal, frame):
         self._reapworkers(os.WNOHANG)
 
     def _reapworkers(self, options):
         while self._workerpids:
             try:
                 pid, _status = os.waitpid(-1, options)
             except OSError as inst:
                 if inst.errno == errno.EINTR:
                     continue
                 if inst.errno != errno.ECHILD:
                     raise
                 # no child processes at all (reaped by other waitpid()?)
                 self._workerpids.clear()
                 return
             if pid == 0:
                 # no waitable child processes
                 return
             self.ui.log(b'cmdserver', b'worker process exited (pid=%d)\n', pid)
             self._workerpids.discard(pid)
 
     def _runworker(self, conn):
         signal.signal(signal.SIGCHLD, self._oldsigchldhandler)
         _initworkerprocess()
         h = self._servicehandler
         try:
             _serverequest(
                 self.ui,
                 self.repo,
                 conn,
                 h.createcmdserver,
                 prereposetups=[self._reposetup],
             )
         finally:
             gc.collect()  # trigger __del__ since worker process uses os._exit
 
     def _reposetup(self, ui, repo):
         if not repo.local():
             return
 
         class unixcmdserverrepo(repo.__class__):
             def close(self):
                 super(unixcmdserverrepo, self).close()
                 try:
                     self._cmdserveripc.send(self.root)
                 except socket.error:
                     self.ui.log(
                         b'cmdserver', b'failed to send repo root to master\n'
                     )
 
         repo.__class__ = unixcmdserverrepo
         repo._cmdserveripc = self._workeripc
 
         cachedrepo = self._repoloader.get(repo.root)
         if cachedrepo is None:
             return
         repo.ui.log(b'repocache', b'repo from cache: %s\n', repo.root)
         repocache.copycache(cachedrepo, repo)