[PATCH 2 of 2] osutil: implement setprocname to set process title for some platforms

[Gregory Szorc]

On Sun, Nov 13, 2016 at 6:18 AM, Yuya Nishihara <yuya at tcha.org> wrote:

> On Fri, 11 Nov 2016 21:14:37 +0000, Jun Wu wrote:
> > # HG changeset patch
> > # User Jun Wu <quark at fb.com>
> > # Date 1478898677 0
> > #      Fri Nov 11 21:11:17 2016 +0000
> > # Node ID 4ccb6bcaf25a741d3a0d8abd6c674573ef76069a
> > # Parent  98761d64eaaf67f3bdb99f3f80a57910e2624b78
> > # Available At https://bitbucket.org/quark-zju/hg-draft
> > #              hg pull https://bitbucket.org/quark-zju/hg-draft -r
> 4ccb6bcaf25a
> > osutil: implement setprocname to set process title for some platforms
>
> Seems fine. We can't guarantee argv[i] is null terminated for all i, but
> that seems less dangerous since the last argv[i] always has '\0'.
>
> A few nits.
>
> > --- a/mercurial/osutil.c
> > +++ b/mercurial/osutil.c
> > @@ -728,4 +728,59 @@ bail:
> >
> >  #endif /* CMSG_LEN */
> > +
> > +/* Check what setprocname method we can use:
> > + * a. use setproctitle if it's available - works in FreeBSD
> > + * b. rewrite **argv buffer in place - works in Linux and OS X
> > + * Note: for "b.", we need Python 2, because Python 3's Py_GetArgcArgv
> returns
> > + * the copied wchar_t **argv, not the original char **argv. */
> > +#if defined(HAVE_SETPROCTITLE)
> > +#define setprocname_method 'a'
> > +#elif (defined(__linux__) || defined(__APPLE__)) && PY_MAJOR_VERSION ==
> 2
> > +#define setprocname_method 'b'
> > +#else
> > +#undef setprocname_method
> > +#endif
>
> Lowercase macro name and char-type value seem not common. Can you change
> them
> to old-school macros such as SETPROCNAME_USE_SETPROCTITLE?
>
> > +#ifdef setprocname_method
> > +static PyObject *setprocname(PyObject *self, PyObject *args)
> > +{
> > +     const char *name = NULL;
> > +     if (!PyArg_ParseTuple(args, "s", &name))
> > +             return NULL;
> > +
> > +#if 'a' == setprocname_method
> > +     setproctitle("%s", name);
> > +#elif 'b' == setprocname_method
> > +     static char *argvstart = NULL;
> > +     static size_t argvsize = 0;
>
> Strictly speaking, these declarations should be moved to the block head.
> (But
> almost all modern compilers but for MSVC would allow mixed declarations.)
>

To clarify, C99 allows declarations anywhere. MSVC 2013+ support this C99
feature. However, Python 2.7 is built with MSVC 2008, so we're effectively
stuck with what that version supports as long as we support Python 2.
Alternatively, we could compile code as C++. That gets messy with the C
interop we need for Python C extensions and CFFI, however.


>
> > +     if (argvstart == NULL) {
> > +             int argc = 0, i;
> > +             char **argv = NULL;
> > +             extern void Py_GetArgcArgv(int *argc, char ***argv);
> > +             Py_GetArgcArgv(&argc, &argv);
> > +
> > +             /* Check the memory we can use. Typically, argv[i] and
> > +              * argv[i+1] are separated by a NULL character. */
> > +             if (argc > 0) {
> > +                     argvstart = argv[0];
> > +                     argvsize = strlen(argv[0]) + 1;
> > +                     for (i = 1; i < argc; ++i) {
> > +                             if (argv[i] == argvstart + argvsize)
> > +                                     argvsize += strlen(argv[i]) + 1;
> > +                     }
> > +             }
>
> Perhaps this loop can start with argvstart = argv[0], argvsize = 0, i = 0.
>
> > +     }
> > +
> > +     if (argvstart && argvsize > 1) {
> > +             int n = snprintf(argvstart, argvsize - 1, "%s", name);
>
> IIRC, snprintf() takes size including the last null byte and null
> termination
> is guaranteed.
>
> > +             if (n >= 0 && (size_t)n < argvsize)
> > +                     memset(argvstart + n, 0, argvsize - n);
> > +     }
> > +#endif
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