lock: while releasing, unlink lockfile even if the release function throws
Consider a hypothetical bug in the release function that causes it to raise an
exception. Also consider the bisect command, which saves its state in a finally
clause. Saving the state requires acquiring the wlock.
If we don't unlink the lockfile when the exception is thrown, we'll try to
acquire the wlock again. We're going to try and acquire a lock again while our
old lockfile is on disk. The PID on disk is our own, and of course we're still
running, so we won't take over the lock. Hence we'll be stuck waiting for a
lock that we left behind ourselves.
To avoid this, always unlink the lockfile. This preserves the invariant that
self.held > 0 is equivalent to the lockfile existing on disk.
#!/usr/bin/env python
# Undump a dump from dumprevlog
# $ hg init
# $ undumprevlog < repo.dump
import sys
from mercurial import revlog, node, scmutil, util, transaction
for fp in (sys.stdin, sys.stdout, sys.stderr):
util.setbinary(fp)
opener = scmutil.opener('.', False)
tr = transaction.transaction(sys.stderr.write, opener, "undump.journal")
while True:
l = sys.stdin.readline()
if not l:
break
if l.startswith("file:"):
f = l[6:-1]
r = revlog.revlog(opener, f)
print f
elif l.startswith("node:"):
n = node.bin(l[6:-1])
elif l.startswith("linkrev:"):
lr = int(l[9:-1])
elif l.startswith("parents:"):
p = l[9:-1].split()
p1 = node.bin(p[0])
p2 = node.bin(p[1])
elif l.startswith("length:"):
length = int(l[8:-1])
sys.stdin.readline() # start marker
d = sys.stdin.read(length)
sys.stdin.readline() # end marker
r.addrevision(d, tr, lr, p1, p2)
tr.close()