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
cHg
===
A fast client for Mercurial command server running on Unix.
Install:
$ make
$ make install
Usage:
$ chg help # show help of Mercurial
$ alias hg=chg # replace hg command
$ chg --kill-chg-daemon # terminate background server
Environment variables:
Although cHg tries to update environment variables, some of them cannot be
changed after spawning the server. The following variables are specially
handled:
* configuration files are reloaded automatically by default.
* CHGHG or HG specifies the path to the hg executable spawned as the
background command server.
The following variables are available for testing:
* CHGDEBUG enables debug messages.
* CHGSOCKNAME specifies the socket path of the background cmdserver.
* CHGTIMEOUT specifies how many seconds chg will wait before giving up
connecting to a cmdserver. If it is 0, chg will wait forever. Default: 60