The new std.process is ready for review

[Steven Schveighoffer]

On Sat, 09 Mar 2013 11:05:14 -0500, Lars T. Kyllingstad  
<public at kyllingen.net> wrote:

> On Wednesday, 6 March 2013 at 16:45:51 UTC, Steven Schveighoffer wrote:
>> On Tue, 05 Mar 2013 17:38:09 -0500, Vladimir Panteleev  
>> <vladimir at thecybershadow.net> wrote:
>
>>> I've also initially tried writing a different program:
>>>
>>> [...]
>>
>> Linux should work here.  From what I can tell, you are doing it right.
>>
>> If I get some time, I'll try and debug this.
>
> I think I know what the problem is, and it sucks bigtime. :(
>
> Since the child process inherits the parent's open file descriptors,  
> both ends of a pipe will be open in the child process.  We have  
> separated pipe creation and process creation, so spawnProcess() knows  
> nothing about the "other" end of the pipe it receives, and is therefore  
> unable to close it.
>
> In this particular case, the problem is that "sort" doesn't do anything  
> until it receives EOF on standard input, which never happens, because  
> even though the write end of the pipe is closed in the parent process,  
> it is still open in the child.

Oh crap, that is bad.

Unlike Windows which is an opt-in strategy, unix has an opt-out strategy  
(there is the F_CLOEXEC flag).  For consistency, I think it would be good  
to close all the file descriptors before calling exec.

> I don't know how to solve this in a good way.  I can think of a few  
> alternatives, and they all suck:
>
> 1. Make a "special" spawnProcess() function for pipe redirection.
> 2. Use the "process object" approach, like Tango and Qt.
> 3. After fork(), in the child process, loop over the full range of  
> possible file descriptors and close the ones we don't want open.
>
> The last one would let us keep the current API (and would have the added  
> benefit of cleaning up unused FDs) but I have no idea how it would  
> impact performance.

I think 3 is the correct answer, it is consistent with Windows, and the  
most logical behavior.  For instance, if other threads are open and doing  
other things that aren't related (like network sockets), those too will be  
inherited!  We should close all file descriptors.

How do you loop over all open ones?  Just curious :)

-Steve