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
# Extension to write out fake unsupported records into the merge state
#
#
from __future__ import absolute_import
from mercurial import (
cmdutil,
merge,
)
cmdtable = {}
command = cmdutil.command(cmdtable)
@command('fakemergerecord',
[('X', 'mandatory', None, 'add a fake mandatory record'),
('x', 'advisory', None, 'add a fake advisory record')], '')
def fakemergerecord(ui, repo, *pats, **opts):
with repo.wlock():
ms = merge.mergestate.read(repo)
records = ms._makerecords()
if opts.get('mandatory'):
records.append(('X', 'mandatory record'))
if opts.get('advisory'):
records.append(('x', 'advisory record'))
ms._writerecords(records)