Please ignore, send to the list by accident.
On Fri, Jul 25, 2025 at 11:59 AM Tomasz Kamiński <tkami...@redhat.com>
wrote:
> Instead of using "::__overflow" using "__fwritable" and handle
> flushing empty writebuf in constructor.
> ---
> This removes unconditional flushing in _File constructor, and
> replace it with writeability check only. The flush is performed
> conditionally in _File_sink constructor, only if the _M_writebuf
> is empty. Otherwise it wil lbe done on first overflow.
>
> I looked into testing configure and testing that, just done edits
> that looked like what I should do.
>
> libstdc++-v3/acinclude.m4 | 7 ++++---
> libstdc++-v3/include/std/print | 22 +++++++++++++++-------
> 2 files changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> index 1774e81d617..0dd9375a278 100644
> --- a/libstdc++-v3/acinclude.m4
> +++ b/libstdc++-v3/acinclude.m4
> @@ -5824,10 +5824,11 @@ AC_LANG_SAVE
> using f2_type = size_t (*)(FILE*) noexcept;
> }
> ],[
> - f1_type f1 = &::__flbf;
> - f2_type f2 = &::__fbufsize;
> + f1_type twriteable = &::__fwriteable;
> + f1_type tblk = &::__flbf;
> + f2_type pbufsize = &::__fbufsize;
> FILE* f = ::fopen("", "");
> - int i = ::__overflow(f, EOF);
> + bool writeable = ::__fwriteable(f);
> bool line_buffered = ::__flbf(f);
> size_t bufsz = ::__fbufsize(f);
> char*& pptr = f->_IO_write_ptr;
> diff --git a/libstdc++-v3/include/std/print
> b/libstdc++-v3/include/std/print
> index 668eee366bd..4ffc18e780c 100644
> --- a/libstdc++-v3/include/std/print
> +++ b/libstdc++-v3/include/std/print
> @@ -57,6 +57,7 @@ namespace __format
> {
> #if _GLIBCXX_USE_STDIO_LOCKING && _GLIBCXX_USE_GLIBC_STDIO_EXT
> // These are defined in <stdio_ext.h> but we don't want to include that.
> + extern "C" int __fwritable(FILE*) noexcept;
> extern "C" int __flbf(FILE*) noexcept;
> extern "C" size_t __fbufsize(FILE*) noexcept;
>
> @@ -70,12 +71,11 @@ namespace __format
> _File(FILE* __f) : _M_file(__f)
> {
> ::flockfile(__f);
> - // Ensure stream is in write mode and allocate buffer if needed:
> - if (::__overflow(__f, EOF) == EOF)
> + // Ensure stream is in write mode
> + if (!__fwritable(__f))
> {
> - const int __err = errno;
> ::funlockfile(__f);
> - __throw_system_error(__err);
> + __throw_system_error(EACCES);
> }
> }
>
> @@ -144,9 +144,17 @@ namespace __format
> _File_sink(FILE* __f, bool __add_newline)
> : _M_file(__f), _M_add_newline(__add_newline)
> {
> - if (!_M_file._M_unbuffered())
> - // Write directly to the FILE's output buffer.
> - this->_M_reset(_M_file._M_write_buf());
> + if (_M_file._M_unbuffered())
> + return;
> +
> + std::span<char> __writebuf = _M_file._M_write_buf();
> + if (__writebuf.empty())
> + {
> + _M_file._M_flush();
> + __writebuf = _M_file._M_write_buf();
> + }
> + // Write directly to the FILE's output buffer.
> + this->_M_reset(__writebuf);
> }
>
> ~_File_sink() noexcept(false)
> --
> 2.49.0
>
>
