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
#!/usr/bin/env python
# Dump revlogs as raw data stream
# $ find .hg/store/ -name "*.i" | xargs dumprevlog > repo.dump
from __future__ import absolute_import, print_function
import sys
from mercurial import (
node,
revlog,
util,
)
for fp in (sys.stdin, sys.stdout, sys.stderr):
util.setbinary(fp)
for f in sys.argv[1:]:
binopen = lambda fn: open(fn, 'rb')
r = revlog.revlog(binopen, f)
print("file:", f)
for i in r:
n = r.node(i)
p = r.parents(n)
d = r.revision(n)
print("node:", node.hex(n))
print("linkrev:", r.linkrev(i))
print("parents:", node.hex(p[0]), node.hex(p[1]))
print("length:", len(d))
print("-start-")
print(d)
print("-end-")