I’m assuming that OS X’s method for setting a pthread’s cwd is private API.
Unless a better way to accomplish the same end-goal is in the works, is there
any way to expose it?
In regards to Linux, the more I look at this, the less attractive posix_spawn()
appears as a way of implementing this on that platform. I’ll likely have a
better idea how to approach this following some prototyping later tonight, but
my current line of thinking involves vfork() -> unshare() -> chdir() ->
execve().
Dan
> On Dec 18, 2015, at 12:39 PM, Pierre Habouzit <pie...@habouzit.net> wrote:
>
> FWIW Glibc implements posix_spawn on posix platforms in terms of {,v}fork +
> execve.
> So that means that SIGCHLD can be used.
>
> I don’t think linux has per-thread wd, since linux has had atcalls for a very
> long time, which makes this system interface not useful and only weird
> (pthread_{,f}chdir).
>
> I don’t think there’s a good way to fix this beside asking for POSIX to have
> a posix_spawnattr_setwd(attr, const char *); or changing it around the spawn,
> which of course, is bad and racy
>
> The other alternative is to use a trampoline execv() when -[NSTask
> currentDirectoryPath] has been set that will just chdir() and exec's again.
> it’s not really pretty but does the job. Given that this should be the
> exception and not the rule, maybe that’s acceptable.
>
>
> -Pierre
>
>> On Dec 18, 2015, at 11:37 AM, David Smith via swift-corelibs-dev
>> <swift-corelibs-dev@swift.org> wrote:
>>
>> One issue that we ran into in the ObjC NSTask is setting the current working
>> directory in the child process. We worked around the lack of an API for that
>> by using per-thread working directories, which is kind of awful. I'm not up
>> to date on what the best approach to use for this on Linux would be; it
>> sounds like clone() can do it, but I don't know if that's exposed at the
>> posix_spawn level at all.
>>
>> David
>>
>>> On Dec 18, 2015, at 11:08 AM, Dan Stenmark via swift-corelibs-dev
>>> <swift-corelibs-dev@swift.org> wrote:
>>>
>>> I hope to take a crack at implementing some of NSTask this weekend. What
>>> are the recommended posix_spawnattr_t flags that should be set? Do we also
>>> want to take the opportunity to expose the ability to override some of
>>> these flags (like POSIX_SPAWN_SETPGROUP) or do we want to avoid tying this
>>> with posix_spawn() too closely?
>>>
>>> Dan
>>> _______________________________________________
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>>> swift-corelibs-dev@swift.org
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>>
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