Mercurial > hg-stable
comparison mercurial/lock.py @ 32088:0d892d820a51 stable
lock: avoid unintentional lock acquisition at failure of readlock
Acquiring lock by vfs.makelock() and getting lock holder (aka
"locker") information by vfs.readlock() aren't atomic action.
Therefore, failure of the former doesn't ensure success of the latter.
Before this patch, lock is unintentionally acquired, if ENOENT
causes failure of vfs.readlock() while 5 times retrying, because
lock._trylock() returns to caller silently after retrying, and
lock.lock() assumes that lock._trylock() returns successfully only if
lock is acquired.
In this case, lock symlink (or file) isn't created, even though lock
is treated as acquired in memory.
To avoid this issue, this patch makes lock._trylock() raise
LockHeld(EAGAIN) at the end of it, if lock isn't acquired while
retrying.
An empty "locker" meaning "busy for frequent lock/unlock by many
processes" might appear in an abortion message, if lock acquisition
fails. Therefore, this patch also does:
- use '%r' to increase visibility of "locker", even if it is empty
- show hint message to explain what empty "locker" means
author | FUJIWARA Katsunori <foozy@lares.dti.ne.jp> |
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date | Mon, 01 May 2017 19:59:13 +0900 |
parents | e1938d6051da |
children | 1b758105b5c7 |
comparison
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32087:e1938d6051da | 32088:0d892d820a51 |
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148 self.vfs.join(self.f), self.desc, | 148 self.vfs.join(self.f), self.desc, |
149 locker) | 149 locker) |
150 else: | 150 else: |
151 raise error.LockUnavailable(why.errno, why.strerror, | 151 raise error.LockUnavailable(why.errno, why.strerror, |
152 why.filename, self.desc) | 152 why.filename, self.desc) |
153 | |
154 if not self.held: | |
155 # use empty locker to mean "busy for frequent lock/unlock | |
156 # by many processes" | |
157 raise error.LockHeld(errno.EAGAIN, | |
158 self.vfs.join(self.f), self.desc, "") | |
153 | 159 |
154 def _readlock(self): | 160 def _readlock(self): |
155 """read lock and return its value | 161 """read lock and return its value |
156 | 162 |
157 Returns None if no lock exists, pid for old-style locks, and host:pid | 163 Returns None if no lock exists, pid for old-style locks, and host:pid |