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
Source bundle was generated with the following script:
# hg init
# echo a > a
# ln -s a l
# hg ci -Ama -d'0 0'
# mkdir b
# echo a > b/a
# chmod +x b/a
# hg ci -Amb -d'1 0'
$ hg init
$ hg -q pull "$TESTDIR/bundles/test-manifest.hg"
The next call is expected to return nothing:
$ hg manifest
$ hg co
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg manifest
a
b/a
l
$ hg files -vr .
2 a
2 x b/a (glob)
1 l l
$ hg files -r . -X b
a
l
$ hg manifest -v
644 a
755 * b/a
644 @ l
$ hg manifest --debug
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 755 * b/a
047b75c6d7a3ef6a2243bd0e99f94f6ea6683597 644 @ l
$ hg manifest -r 0
a
l
$ hg manifest -r 1
a
b/a
l
$ hg manifest -r tip
a
b/a
l
$ hg manifest tip
a
b/a
l
$ hg manifest --all
a
b/a
l
The next two calls are expected to abort:
$ hg manifest -r 2
abort: unknown revision '2'!
[255]
$ hg manifest -r tip tip
abort: please specify just one revision
[255]