__hscore_open from HsBase.h

[Simon Marlow]

Bulat Ziganshin wrote:
> Hello Simon,
>
> Tuesday, November 14, 2006, 2:31:17 PM, you wrote:
>
>>>>> #ifdef mingw32_HOST_OS
>>>>>         if ((how & O_WRONLY) || (how & O_RDWR) || (how &
>>>>>           O_APPEND)) return _sopen(file,how,_SH_DENYRW,mode);
>>>>>         else
>>>>>           return _sopen(file,how,_SH_DENYWR,mode);
>>>>> #else
>>>>>         return open(file,how,mode);
>>>>> #endif
>>>
>>>> I haven't seen this code before, but I wonder if it's an attempt to
>>>> implement the single-writer multiple-reader locking semantics in
>>>> the Haskell 98 IO library?
>
>>> and second question: HOW this may help this semantics?? in my
>>> investigation, simple 'open' is just fine - it prevents writing by
>>> other processes to the file being written by Haskell program and it
>>> allow to read and write open by other processes of the file that i
>>> only read.
>
>> But does it allow the file to be opened for reading multiple times
>> by the current process?  Perhaps that's the issue.
>
> no problem at all. i even can read file modified by the same process
>
>>> may be it was problems on old windowses? and may be this some bug
>>> and this should be rewritten as DENY_WRITE and DENY_NONE,
>>> correspondingly
>>>
>>> btw, what is a semantics on Unix? is it the same as i mentioned
>>> above?
>
>> On Unix by default you can open a file as many times as you like,
>> both for reading and writing.  To enforce any restrictions you have
>> to use locks.
>
> i.e. no sopen at all? in this case, other parts of library should
> make proper locking for unix.

Yes, we do.  See http://darcs.haskell.org/packages/base/cbits/lockFile.c.

> but for windows, the code above allow to EITHER multiple readers OR
> one writer. to allow multiple readers AND one writer simultaneously,
> it should be written as

No, multiple readers *or* a single writer is what the Haskell spec says.  Go check your Haskell Report.

Cheers,
        Simon