Mercurial > hg
view mercurial/lock.py @ 33766:4c706037adef
wireproto: overhaul iterating batcher code (API)
The remote batching code is difficult to read. Let's improve it.
As part of the refactor, the future returned by method calls on
batchiter() instances is now populated. However, you still need to
consume the results() generator for the future to be set. But at
least now we can stuff the future somewhere and not have to worry
about aligning method call order with result order since you can
use a future to hold the result.
Also as part of the change, we now verify that @batchable generators
yield exactly 2 values. In other words, we enforce their API.
The non-iter batcher has been unused since b6e71f8af5b8. And to my
surprise we had no explicit unit test coverage of it! test-batching.py
has been overhauled to use the iterating batcher.
Since the iterating batcher doesn't allow non-batchable method
calls nor local calls, tests have been updated to reflect reality.
The iterating batcher has been used for multiple releases apparently
without major issue. So this shouldn't cause alarm.
.. api::
@peer.batchable functions must now yield exactly 2 values
Differential Revision: https://phab.mercurial-scm.org/D319
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 09 Aug 2017 23:29:30 -0700 |
parents | 0d892d820a51 |
children | 1b758105b5c7 |
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# 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 . 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 = socket.gethostname() if pycompat.ispy3: result = result.encode(pycompat.sysstr(encoding.encoding), 'replace') 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 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): 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() 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()