__errno_location() like functionality in Cygwin

__errno_location() like functionality in Cygwin

[Dmitry Timoshkov]

Hello.

I'm new to this list. I'd like to know, is it possible to define
my own __errno() function, which will provide functionality like
__errno_location() in linux?

This simple program works in linux, but doesn't under Cygwin:

static int myerrno = 0;
static char buf[256];

int *__errno_location(void)
{
    return &myerrno;
}

int *__errno(void)
{
    return &myerrno;
}

int main(void)
{
    int ret;

    /* provoke an error */
    ret = read(-1, buf, 255);
    printf("ret = %d, myerrno = %d\n", ret, myerrno);

    return 0;
}

Any suggestions?

Thanks in advance.
--
Dmitry.



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Re: __errno_location() like functionality in Cygwin

[Dmitry Timoshkov]

Hello again.

I wrote:

> I'm new to this list. I'd like to know, is it possible to define
> my own __errno() function, which will provide functionality like
> __errno_location() in linux?
> 
> This simple program works in linux, but doesn't under Cygwin:
[sample skipped]

I'm sorry, perhaps I sent too little information to make things to be more clear.

I have installed Cygwin 1.1.8 on win2000 and want to port multithreaded application
that currently works under Linux.

That application allocates for each created thread Thread Local Storage and saves in it
its own errno variable. Application defines its own function __errno_location in which
it returns address of that thread local errno variable. Can anybody shed some light
whether it possible or not to do the same trick under Cygwin? Or just say that it is
impossible?

I searched archives of this mailing list and have read FAQ and documentation about
two possible ways to achieve reentrancy using reent struct. The first method requires
to replace all standard library calls by their _*_r equivalents. That's not an option.
The second method requires to assign _impure_ptr to the pointer of thread local reent
structrure before EVERY libc call. Am I understand it correctly?

Thanks in advance for any pointers and suggestions.
--
Dmitry.



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