debugcommands: add debugwireproto command
We currently don't have a low-level mechanism for sending
arbitrary wire protocol commands. Having a generic and robust
mechanism for sending wire protocol commands, examining wire
data, etc would make it vastly easier to test the wire protocol
and debug server operation. This is a problem I've wanted a
solution for numerous times, especially recently as I've been
hacking on a new version of the wire protocol.
This commit establishes a `hg debugwireproto` command for sending
data to a peer.
The command invents a mini language for specifying actions to take.
This will enable a lot of flexibility for issuing commands and testing
variations for how commands are sent.
Right now, we only support low-level raw sends and receives. These
are probably the least valuable commands to intended users of this
command. But they are the most useful commands to implement to
bootstrap the feature (I've chosen to reimplement test-ssh-proto.t
using this command to prove its usefulness).
My eventual goal of `hg debugwireproto` is to allow calling wire
protocol commands with a human-friendly interface. Essentially,
people can type in a command name and arguments and
`hg debugwireproto` will figure out how to send that on the wire.
I'd love to eventually be able to save the server's raw response
to a file. This would allow us to e.g. call "getbundle" wire
protocol commands easily.
test-ssh-proto.t has been updated to use the new command in lieu
of piping directly to a server process. As part of the transition,
test behavior improved. Before, we piped all request data to the
server at once. Now, we have explicit control over the ordering of
operations. e.g. we can send one command, receive its response,
then send another command. This will allow us to more robustly
test race conditions, buffering behavior, etc.
There were some subtle changes in test behavior. For example,
previous behavior would often send trailing newlines to the server.
The new mechanism doesn't treat literal newlines specially and
requires newlines be escaped in the payload.
Because the new logging code is very low level, it is easy to
introduce race conditions in tests. For example, the number of bytes
returned by a read() may vary depending on load. This is why tests
make heavy use of "readline" for consuming data: the result of
that operation should be deterministic and not subject to race
conditions. There are still some uses of "readavailable." However,
those are only for reading from stderr. I was able to reproduce
timing issues with my system under load when using "readavailable"
globally. But if I "readline" to grab stdout, "readavailable"
appears to work deterministically for stderr. I think this is
because the server writes to stderr first. As long as the OS
delivers writes to pipes in the same order they were made, this
should work. If there are timing issues, we can introduce a
mechanism to readline from stderr.
Differential Revision: https://phab.mercurial-scm.org/D2392
# lock.py - simple advisory locking scheme for mercurial
#
# Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
#
# 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 contextlib
import errno
import os
import socket
import time
import warnings
from .i18n import _
from . import (
encoding,
error,
pycompat,
util,
)
def _getlockprefix():
"""Return a string which is used to differentiate pid namespaces
It's useful to detect "dead" processes and remove stale locks with
confidence. Typically it's just hostname. On modern linux, we include an
extra Linux-specific pid namespace identifier.
"""
result = encoding.strtolocal(socket.gethostname())
if pycompat.sysplatform.startswith('linux'):
try:
result += '/%x' % os.stat('/proc/self/ns/pid').st_ino
except OSError as ex:
if ex.errno not in (errno.ENOENT, errno.EACCES, errno.ENOTDIR):
raise
return result
def trylock(ui, vfs, lockname, timeout, warntimeout, *args, **kwargs):
"""return an acquired lock or raise an a LockHeld exception
This function is responsible to issue warnings and or debug messages about
the held lock while trying to acquires it."""
def printwarning(printer, locker):
"""issue the usual "waiting on lock" message through any channel"""
# show more details for new-style locks
if ':' in locker:
host, pid = locker.split(":", 1)
msg = _("waiting for lock on %s held by process %r "
"on host %r\n") % (l.desc, pid, host)
else:
msg = _("waiting for lock on %s held by %r\n") % (l.desc, locker)
printer(msg)
l = lock(vfs, lockname, 0, *args, dolock=False, **kwargs)
debugidx = 0 if (warntimeout and timeout) else -1
warningidx = 0
if not timeout:
warningidx = -1
elif warntimeout:
warningidx = warntimeout
delay = 0
while True:
try:
l._trylock()
break
except error.LockHeld as inst:
if delay == debugidx:
printwarning(ui.debug, inst.locker)
if delay == warningidx:
printwarning(ui.warn, inst.locker)
if timeout <= delay:
raise error.LockHeld(errno.ETIMEDOUT, inst.filename,
l.desc, inst.locker)
time.sleep(1)
delay += 1
l.delay = delay
if l.delay:
if 0 <= warningidx <= l.delay:
ui.warn(_("got lock after %d seconds\n") % l.delay)
else:
ui.debug("got lock after %d seconds\n" % l.delay)
if l.acquirefn:
l.acquirefn()
return l
class lock(object):
'''An advisory lock held by one process to control access to a set
of files. Non-cooperating processes or incorrectly written scripts
can ignore Mercurial's locking scheme and stomp all over the
repository, so don't do that.
Typically used via localrepository.lock() to lock the repository
store (.hg/store/) or localrepository.wlock() to lock everything
else under .hg/.'''
# lock is symlink on platforms that support it, file on others.
# symlink is used because create of directory entry and contents
# are atomic even over nfs.
# old-style lock: symlink to pid
# new-style lock: symlink to hostname:pid
_host = None
def __init__(self, vfs, file, timeout=-1, releasefn=None, acquirefn=None,
desc=None, inheritchecker=None, parentlock=None,
dolock=True):
self.vfs = vfs
self.f = file
self.held = 0
self.timeout = timeout
self.releasefn = releasefn
self.acquirefn = acquirefn
self.desc = desc
self._inheritchecker = inheritchecker
self.parentlock = parentlock
self._parentheld = False
self._inherited = False
self.postrelease = []
self.pid = self._getpid()
if dolock:
self.delay = self.lock()
if self.acquirefn:
self.acquirefn()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, exc_tb):
self.release()
def __del__(self):
if self.held:
warnings.warn("use lock.release instead of del lock",
category=DeprecationWarning,
stacklevel=2)
# ensure the lock will be removed
# even if recursive locking did occur
self.held = 1
self.release()
def _getpid(self):
# wrapper around util.getpid() to make testing easier
return util.getpid()
def lock(self):
timeout = self.timeout
while True:
try:
self._trylock()
return self.timeout - timeout
except error.LockHeld as inst:
if timeout != 0:
time.sleep(1)
if timeout > 0:
timeout -= 1
continue
raise error.LockHeld(errno.ETIMEDOUT, inst.filename, self.desc,
inst.locker)
def _trylock(self):
if self.held:
self.held += 1
return
if lock._host is None:
lock._host = _getlockprefix()
lockname = '%s:%d' % (lock._host, self.pid)
retry = 5
while not self.held and retry:
retry -= 1
try:
self.vfs.makelock(lockname, self.f)
self.held = 1
except (OSError, IOError) as why:
if why.errno == errno.EEXIST:
locker = self._readlock()
if locker is None:
continue
# special case where a parent process holds the lock -- this
# is different from the pid being different because we do
# want the unlock and postrelease functions to be called,
# but the lockfile to not be removed.
if locker == self.parentlock:
self._parentheld = True
self.held = 1
return
locker = self._testlock(locker)
if locker is not None:
raise error.LockHeld(errno.EAGAIN,
self.vfs.join(self.f), self.desc,
locker)
else:
raise error.LockUnavailable(why.errno, why.strerror,
why.filename, self.desc)
if not self.held:
# use empty locker to mean "busy for frequent lock/unlock
# by many processes"
raise error.LockHeld(errno.EAGAIN,
self.vfs.join(self.f), self.desc, "")
def _readlock(self):
"""read lock and return its value
Returns None if no lock exists, pid for old-style locks, and host:pid
for new-style locks.
"""
try:
return self.vfs.readlock(self.f)
except (OSError, IOError) as why:
if why.errno == errno.ENOENT:
return None
raise
def _testlock(self, locker):
if locker is None:
return None
try:
host, pid = locker.split(":", 1)
except ValueError:
return locker
if host != lock._host:
return locker
try:
pid = int(pid)
except ValueError:
return locker
if util.testpid(pid):
return locker
# if locker dead, break lock. must do this with another lock
# held, or can race and break valid lock.
try:
l = lock(self.vfs, self.f + '.break', timeout=0)
self.vfs.unlink(self.f)
l.release()
except error.LockError:
return locker
def testlock(self):
"""return id of locker if lock is valid, else None.
If old-style lock, we cannot tell what machine locker is on.
with new-style lock, if locker is on this machine, we can
see if locker is alive. If locker is on this machine but
not alive, we can safely break lock.
The lock file is only deleted when None is returned.
"""
locker = self._readlock()
return self._testlock(locker)
@contextlib.contextmanager
def inherit(self):
"""context for the lock to be inherited by a Mercurial subprocess.
Yields a string that will be recognized by the lock in the subprocess.
Communicating this string to the subprocess needs to be done separately
-- typically by an environment variable.
"""
if not self.held:
raise error.LockInheritanceContractViolation(
'inherit can only be called while lock is held')
if self._inherited:
raise error.LockInheritanceContractViolation(
'inherit cannot be called while lock is already inherited')
if self._inheritchecker is not None:
self._inheritchecker()
if self.releasefn:
self.releasefn()
if self._parentheld:
lockname = self.parentlock
else:
lockname = '%s:%s' % (lock._host, self.pid)
self._inherited = True
try:
yield lockname
finally:
if self.acquirefn:
self.acquirefn()
self._inherited = False
def release(self):
"""release the lock and execute callback function if any
If the lock has been acquired multiple times, the actual release is
delayed to the last release call."""
if self.held > 1:
self.held -= 1
elif self.held == 1:
self.held = 0
if self._getpid() != self.pid:
# we forked, and are not the parent
return
try:
if self.releasefn:
self.releasefn()
finally:
if not self._parentheld:
try:
self.vfs.unlink(self.f)
except OSError:
pass
# The postrelease functions typically assume the lock is not held
# at all.
if not self._parentheld:
for callback in self.postrelease:
callback()
# Prevent double usage and help clear cycles.
self.postrelease = None
def release(*locks):
for lock in locks:
if lock is not None:
lock.release()