worker: rewrite error handling so os._exit covers all cases
Previously the worker error handling is like:
pid = os.fork() --+
if pid == 0: |
.... | problematic
.... --+
try: --+
.... | worker error handling
--+
If a signal arrives when Python is executing the "problematic" lines, an
external error handling (dispatch.py) will take over the control flow and
it's no longer guaranteed "os._exit" is called (see
86cd09bc13ba for why it
is necessary).
This patch rewrites the error handling so it covers all possible code paths
for a worker even during fork.
Note: "os.getpid() == parentpid" is used to test if the process is parent or
not intentionally, instead of checking "pid", because "pid = os.fork()" may
be not atomic - it's possible that that a signal hits the worker before the
assignment completes [1]. The newly added test replaces "os.fork" to
exercise that extreme case.
[1]: CPython compiles "pid = os.fork()" to 2 byte codes: "CALL_FUNCTION" and
"STORE_FAST", so it's probably not atomic:
def f():
pid = os.fork()
dis.dis(f)
2 0 LOAD_GLOBAL 0 (os)
3 LOAD_ATTR 1 (fork)
6 CALL_FUNCTION 0
9 STORE_FAST 0 (pid)
12 LOAD_CONST 0 (None)
15 RETURN_VALUE
from __future__ import absolute_import
import os
import sys
import time
from mercurial import (
commands,
hg,
ui as uimod,
util,
)
TESTDIR = os.environ["TESTDIR"]
BUNDLEPATH = os.path.join(TESTDIR, 'bundles', 'test-no-symlinks.hg')
# only makes sense to test on os which supports symlinks
if not getattr(os, "symlink", False):
sys.exit(80) # SKIPPED_STATUS defined in run-tests.py
u = uimod.ui.load()
# hide outer repo
hg.peer(u, {}, '.', create=True)
# clone with symlink support
hg.clone(u, {}, BUNDLEPATH, 'test0')
repo = hg.repository(u, 'test0')
# wait a bit, or the status call wont update the dirstate
time.sleep(1)
commands.status(u, repo)
# now disable symlink support -- this is what os.symlink would do on a
# non-symlink file system
def symlink_failure(src, dst):
raise OSError(1, "Operation not permitted")
os.symlink = symlink_failure
def islink_failure(path):
return False
os.path.islink = islink_failure
# dereference links as if a Samba server has exported this to a
# Windows client
for f in 'test0/a.lnk', 'test0/d/b.lnk':
os.unlink(f)
fp = open(f, 'wb')
fp.write(util.readfile(f[:-4]))
fp.close()
# reload repository
u = uimod.ui.load()
repo = hg.repository(u, 'test0')
commands.status(u, repo)
# try cloning a repo which contains symlinks
u = uimod.ui.load()
hg.clone(u, {}, BUNDLEPATH, 'test1')