[phobos] std.process Windows blocker

[Steve Schveighoffer]

First, those functions are unavailable to D programs, because that is the microsoft runtime, D uses the DMC runtime (DMC does have equivalent functions for those).  Second, getting the file descriptor, or creating a FILE * from a file descriptor, are not good enough.

To create a pipe, I need to use CreatePipe on Windows, or else a C-library wrapper (on Microsoft, it's _pipe).

The problem is, CreatePipe returns HANDLEs, which are not file descriptors.  So I need a way to transform HANDLEs into file descriptors.  With Microsoft's runtime there are two functions:

http://msdn.microsoft.com/en-us/library/ks2530z6%28VS.71%29.aspx
http://msdn.microsoft.com/en-us/library/bdts1c9x%28VS.71%29.aspx

With DMC, there are no such functions (including a _pipe equivalent).  However, Walter has showed me some internal DMC runtime code, which I can port to D to get it to work properly.

But it does raise the concern -- we are depending on 20-25 year old code that may not allow us to write to newer OS APIs, and which leaves some aspects of I/O (arguably one of the most important performance-oriented parts of a standard lib) closed to innovation.  I think eventually, it would be best for phobos to ditch dependence on FILE *, and I would argue, the C runtime in general.  Of course, the C runtime should be *available* to people who want to use it, but Phobos shouldn't use it.

For a good example of why this absolutely sucks, see what the original author of std.process had to do to get shell() to work on Windows:

version (Windows) string shell(string cmd)
{
    // Generate a random filename
    Appender!string a;
    foreach (ref e; 0 .. 8)
    {
        formattedWrite(a, "%x", rndGen.front);
        rndGen.popFront;
    }
    auto filename = a.data;
    scope(exit) if (exists(filename)) remove(filename);
    errnoEnforce(system(cmd ~ "> " ~ filename) == 0);
    return readText(filename);
}

-Steve



----- Original Message ----
> From: Andrei Alexandrescu <andrei at erdani.com>
> http://msdn.microsoft.com/en-us/library/ms235401%28VS.80%29.aspx
http://msdn.microsoft.com/en-us/library/ms235351%28VS.80%29.aspx

Andrei

Lars 
> Tandle Kyllingstad wrote:
> On Tue, 2010-05-04 at 13:28 -0700, Walter 
> Bright wrote:
>> Lars Tandle Kyllingstad wrote:
>>> On Mon, 
> 2010-05-03 at 18:54 -0700, Steve Schveighoffer wrote:
>>>> I can 
> create pipes by directly calling the Windows system call, the problem is, the C 
> runtime lacks a way of wrapping a Windows HANDLE type into a FILE *. 
> [...]
>>>>    
>>> You'd think that would 
> be a common enough situation to warrant having a
>>> function in the 
> Windows API doing just that -- like POSIX' fdopen().  I
>>> 
> mean, isn't FILE* the de facto file handle standard in the C world?
>> 
> Pipes aren't standard C <g>.
> 
> I didn't mean the pipe 
> creation functions. :)
> 
> On POSIX you have fdopen() to wrap a 
> FILE* handle around an OS file
> descriptor, and fileno() to extract an OS 
> file descriptor from a FILE*
> handle.  These are part of the POSIX 
> specification, and therefore
> available regardless of which runtime is 
> being used.
> 
> If I've understood Steve correctly, the same isn't 
> true on Windows.
> Rather, it seems Microsoft have tucked the 
> corresponding functions away
> in their own C runtime. :(
> 
> 
> -Lars
> 
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