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PATCH for libstdc++/2211 (some discussion held on gcc-bugs)
- To: libstdc++ at gcc dot gnu dot org
- Subject: PATCH for libstdc++/2211 (some discussion held on gcc-bugs)
- From: Loren James Rittle <rittle at latour dot rsch dot comm dot mot dot com>
- Date: Mon, 2 Jul 2001 15:51:49 -0500 (CDT)
- CC: gcc-patches at gcc dot gnu dot org
- Reply-to: rittle at labs dot mot dot com
This patch removes an old hack that was impeding performance when C++
IO is unsynchronized from C IO (actually, it further refines where the
input buffer size of cin must be constrained to a size of 1 byte and
documents that condition). Bootstrapped and checked on
i386-unknown-freebsd4.2. Approved by Benjamin. Applied to mainline
only since it only improves performance.
2001-07-02 Loren J. Rittle <ljrittle@acm.org>
libstdc++/2211
* src/ios.cc (ios_base::Init::_S_ios_create): Rename __bufsize to
__out_bufsize. Add __in_bufsize, document it and use it.
Index: libstdc++-v3/src/ios.cc
===================================================================
RCS file: /cvs/gcc/egcs/libstdc++-v3/src/ios.cc,v
retrieving revision 1.19
diff -c -r1.19 ios.cc
*** ios.cc 2001/06/06 01:31:58 1.19
--- ios.cc 2001/07/02 20:41:25
***************
*** 144,157 ****
void
ios_base::Init::_S_ios_create(bool __sync)
{
! int __bufsize = __sync ? 0 : static_cast<int>(BUFSIZ);
// NB: The file globals.cc creates the four standard files
// with NULL buffers. At this point, we swap out the dummy NULL
// [io]stream objects and buffers with the real deal.
! new (&buf_cout) filebuf(stdout, ios_base::out, __bufsize);
! new (&buf_cin) filebuf(stdin, ios_base::in, 1);
! new (&buf_cerr) filebuf(stderr, ios_base::out, __bufsize);
new (&cout) ostream(&buf_cout);
new (&cin) istream(&buf_cin);
new (&cerr) ostream(&buf_cerr);
--- 144,166 ----
void
ios_base::Init::_S_ios_create(bool __sync)
{
! int __out_bufsize = __sync ? 0 : static_cast<int>(BUFSIZ);
! int __in_bufsize = __sync ? 1 : static_cast<int>(BUFSIZ);
+ #if _GLIBCPP_AVOID_FSEEK
+ // Platforms that prefer to avoid fseek() calls on streams only
+ // get their desire when the C++-layer input buffer size is 1.
+ // This hack hurts performance but keeps correctness across
+ // all types of streams that might be attached to (e.g.) cin.
+ __in_bufsize = 1;
+ #endif
+
// NB: The file globals.cc creates the four standard files
// with NULL buffers. At this point, we swap out the dummy NULL
// [io]stream objects and buffers with the real deal.
! new (&buf_cout) filebuf(stdout, ios_base::out, __out_bufsize);
! new (&buf_cin) filebuf(stdin, ios_base::in, __in_bufsize);
! new (&buf_cerr) filebuf(stderr, ios_base::out, __out_bufsize);
new (&cout) ostream(&buf_cout);
new (&cin) istream(&buf_cin);
new (&cerr) ostream(&buf_cerr);
***************
*** 160,168 ****
cerr.flags(ios_base::unitbuf);
#ifdef _GLIBCPP_USE_WCHAR_T
! new (&buf_wcout) wfilebuf(stdout, ios_base::out, __bufsize);
! new (&buf_wcin) wfilebuf(stdin, ios_base::in, 1);
! new (&buf_wcerr) wfilebuf(stderr, ios_base::out, __bufsize);
new (&wcout) wostream(&buf_wcout);
new (&wcin) wistream(&buf_wcin);
new (&wcerr) wostream(&buf_wcerr);
--- 169,177 ----
cerr.flags(ios_base::unitbuf);
#ifdef _GLIBCPP_USE_WCHAR_T
! new (&buf_wcout) wfilebuf(stdout, ios_base::out, __out_bufsize);
! new (&buf_wcin) wfilebuf(stdin, ios_base::in, __in_bufsize);
! new (&buf_wcerr) wfilebuf(stderr, ios_base::out, __out_bufsize);
new (&wcout) wostream(&buf_wcout);
new (&wcin) wistream(&buf_wcin);
new (&wcerr) wostream(&buf_wcerr);