[Vm-dev] Stdin/stdout/stderr support

[Igor Stasenko]

2008/8/30 David T. Lewis <lewis at mail.msen.com>:
>
> On Fri, Aug 29, 2008 at 10:38:18PM +0200, Bert Freudenberg wrote:
>>
>> Am 29.08.2008 um 22:18 schrieb Igor Stasenko:
>> >
>> >i mean that its better to use file handles which is available on all
>> >platforms. and they actually should be open at the process startup
>>
>> Maybe you misunderstood my patch then.
>>
>> If the image tries to open a file named "/dev/stderr" then the VM now
>> actually returns the pre-opened stderr rather than opening the named
>> file. So this is independent of whether a file named "/dev/stderr"
>> actually does exists or not, and it uses the proper file handles.
>
> Yes this will work, but I agree with Igor.
>
> This approach seems too platform-specific to be included in ./Cross.
> It relies on file path name conventions that apply to some (not all)
> Unix systems, and that do not make sense on other platforms. It introduces
> hidden and undocumented behavior (I will not allow you to close the file
> stream if you happen to have referred to it by some particular path name).
>
> Given that folks agree that the concept of stdin/stdout/stderr should
> be supported in Squeak, then there is no reason not to implement it in
> a way that makes sense on all platforms.  A set of three optional primitives
> is sufficient, and will provide the same access mechanism regardless of platform.
>
> For example, here is the Windows implementation from OSPP:
>
> /*      Answer a two element array containing the sqFile data structure representing
>        standard output stream for my OS process, and a flag (true or false) to indicate
>        whether the sqFile data structure contains a valid HANDLE. If no standard output
>        stream is available for this OS process, the sqFile data structure will contain an
>        invalid HANDLE value, which will result in failures on subsequent accesses. */
>
> EXPORT(sqInt) primitiveGetStdOutput(void) {
>    sqInt thisSession;
>    HANDLE invalid;
>    sqInt result;
>    HANDLE handle;
>    SQFile *file;
>    sqInt fileOop;
>
>        thisSession = sessionIdentifierFrom(interpreterProxy->stackObjectValue(0));
>        invalid = INVALID_HANDLE_VALUE;
>        result = interpreterProxy->instantiateClassindexableSize(interpreterProxy->classArray(), 2);

pushRemappableOop(result)

>        fileOop = interpreterProxy->instantiateClassindexableSize(interpreterProxy->classByteArray(), fileRecordSize());

result = popRemappableOop();

>        file = interpreterProxy->arrayValueOf(fileOop);
>        handle = GetStdHandle(STD_OUTPUT_HANDLE);
>        if (handle != invalid) {
>                interpreterProxy->stObjectatput(result, 2, interpreterProxy->trueObject());
>        } else {
>                interpreterProxy->stObjectatput(result, 2, interpreterProxy->falseObject());
>        }
>        file->file = handle;
>        file->sessionID = thisSession;
>        file->writable = 1;
>        file->lastOp = 0;
>        interpreterProxy->stObjectatput(result, 1, fileOop);
>        interpreterProxy->pop(2);
>        interpreterProxy->push(result);
> }
>
>

Good, but maybe it can be more simplier?
Just return a valid file handle on success, or fail primitive if not.
Also, it can be a single prim (primitiveGetStdFileHandle) , with
additional argument indicating which std stream to return e.g.
0 - for stdin
1 - for stdout
2 - for stderr


-- 
Best regards,
Igor Stasenko AKA sig.