[swift-corelibs-dev] Recommended posix_spawnattr_t for NSTask's implementation

[Pierre Habouzit]

-Pierre

> On Dec 18, 2015, at 11:14 AM, Philippe Hausler via swift-corelibs-dev <swift-corelibs-dev at swift.org> wrote:
> 
> I would definitely say that posix_spawn is the correct path to implement this; that will keep pretty close to the way the one on darwin works;
> 
> Couple of suggestions:
> 
> posix_spawnattr_setsigmask should be set to the empty signal set
> 
> the attribute flags should probably be POSIX_SPAWN_CLOEXEC_DEFAULT | POSIX_SPAWN_SETSIGMASK | POSIX_SPAWN_SETSIGDEF
> 
> You can probably skip QoS since it won’t exist on linux.
> 
> There may be some issue with not having libdispatch to use for a source to watch a DISPATCH_PROC_EXIT but this perhaps could be done via a pthread (not certain on exactly how but perhaps it can be done)

No, it can’t that’s the big problem with posix_spawn() on linux, because the new task isn’t a child with this (or maybe it is on linux I don’t know) and there is no equivalent to the EVFILT_PROC which is the kevent backend for the PROC_EXIT dispatch source thing.

This feature is only available through netlink on linux which is restricted to the root user.

It *may* be that posix_spawn()ed things are children on linux and that a SIGCHLD source should be used instead, which means that NSTask would have to multiplex the SIGCHLD + waitpid() and route them back to the right NSTask().


> It also might be useful in this case to drop down to C similarly as CFXMLInterface - but pick your poison on that one.
> 
> 
>> On Dec 18, 2015, at 11:08 AM, Dan Stenmark via swift-corelibs-dev <swift-corelibs-dev at 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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