Re: [Mingw-users] mingwm10.dll

[James S. <jam...@op...>]

On Tue, 2007-02-13 at 22:10 -0800, Brian Dessent wrote:
> James Steward wrote:
> 
> > If a threaded app is written in C where there's no exception handling,
> > it shouldn't be a problem, right?
> 
> I'm not sure.  But I did notice that if _MT is not defined then stdio.h
> selects faster non-threadsafe versions of getc, putc, getchar, and
> putchar.  So using those functions in a multithreaded C application
> without -mthreads would be a possible example of such a case.  I didn't
> see any other obvious uses of _MT but I didn't really look that hard.

Curious.

I believe the OP uses g++, threads, linked static?  However I'd like to
know whether there is any impact of this for my situation, gcc, threads,
linked dynamic.

I built both my test app and dll with and without -mthreads and diffed
the objdump -D output.  There were a few differences (say about 6 lines)
even though I do not directly use any of the functions that may differ
in stdio.h depending on whether _MT is defined or not (see below).

I do use fgets.  Could that call getc?  Otherwise I wonder why gcc
creates differences in the compiled code?

Also, the thread cleanup helper dll was not in the list according to
objdump -p of the -mthreads built version, so it must be a g++ thing
only?

I guess so long as one thread only accesses a file using the non thread
safe versions of the functions (below) there would be no danger of
corruption.

Regards,
James.

#if !defined _MT

__CRT_INLINE int __cdecl getc (FILE* __F)
{
  return (--__F->_cnt >= 0)
    ?  (int) (unsigned char) *__F->_ptr++
    : _filbuf (__F);
}

__CRT_INLINE int __cdecl putc (int __c, FILE* __F)
{
  return (--__F->_cnt >= 0)
    ?  (int) (unsigned char) (*__F->_ptr++ = (char)__c)
    :  _flsbuf (__c, __F);
}

__CRT_INLINE int __cdecl getchar (void)
{
  return (--stdin->_cnt >= 0)
    ?  (int) (unsigned char) *stdin->_ptr++
    : _filbuf (stdin);
}

__CRT_INLINE int __cdecl putchar(int __c)
{
  return (--stdout->_cnt >= 0)
    ?  (int) (unsigned char) (*stdout->_ptr++ = (char)__c)
    :  _flsbuf (__c, stdout);}

#else  /* Use library functions.  */

_CRTIMP int __cdecl     getc (FILE*);
_CRTIMP int __cdecl     putc (int, FILE*);
_CRTIMP int __cdecl     getchar (void);
_CRTIMP int __cdecl     putchar (int);

#endif