mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-26 04:31:03 +00:00
2a99e2398d
This patch fixes BZ #27777 "fclose does a linear search, takes ages when many FILE* are opened". Simply put, the master list of opened (FILE*), namely _IO_list_all, is a singly-linked list. As a consequence, the removal of a single element is in O(N), which cripples the performance of fclose(). The patch switches to a doubly-linked list, yielding O(1) removal. The one padding field in struct _IO_FILE, __pad5, is renamed to _prevchain for a doubly-linked list. Since fields in struct _IO_FILE after the _lock field are internal to glibc and opaque to applications. We can change them as long as the size of struct _IO_FILE is unchanged, which is checked as the part of glibc ABI with sizes of _IO_2_1_stdin_, _IO_2_1_stdout_ and _IO_2_1_stderr_. NB: When _IO_vtable_offset (fp) == 0, copy relocation will cover the whole struct _IO_FILE. Otherwise, only fields up to the _lock field will be copied to applications at run-time. It is used to check if the _prevchain field can be safely accessed. After opening 2 million (FILE*), the fclose() of 100 of them takes quite a few seconds without the patch, and under 2 seconds with it on a loaded machine. No test is added since there are no functional changes. Co-Authored-By: H.J. Lu <hjl.tools@gmail.com> Signed-off-by: Alexandre Ferrieux <alexandre.ferrieux@orange.com> Signed-off-by: H.J. Lu <hjl.tools@gmail.com> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
73 lines
2.8 KiB
C
73 lines
2.8 KiB
C
/* Copyright (C) 1993-2024 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>.
|
|
|
|
As a special exception, if you link the code in this file with
|
|
files compiled with a GNU compiler to produce an executable,
|
|
that does not cause the resulting executable to be covered by
|
|
the GNU Lesser General Public License. This exception does not
|
|
however invalidate any other reasons why the executable file
|
|
might be covered by the GNU Lesser General Public License.
|
|
This exception applies to code released by its copyright holders
|
|
in files containing the exception. */
|
|
|
|
|
|
/* This file provides definitions of _IO_2_1_stdin_, _IO_2_1_stdout_,
|
|
and _IO_2_1_stderr_, the default values of stdin, stdout, stderr.
|
|
See oldstdfiles.c for glibc 2.0 legacy definitions without wide
|
|
character support. */
|
|
|
|
#include "libioP.h"
|
|
|
|
#ifdef _IO_MTSAFE_IO
|
|
# define DEF_STDFILE(NAME, FD, CHAIN, FLAGS) \
|
|
static _IO_lock_t _IO_stdfile_##FD##_lock = _IO_lock_initializer; \
|
|
static struct _IO_wide_data _IO_wide_data_##FD \
|
|
= { ._wide_vtable = &_IO_wfile_jumps }; \
|
|
struct _IO_FILE_plus NAME \
|
|
= {FILEBUF_LITERAL(CHAIN, FLAGS, FD, &_IO_wide_data_##FD), \
|
|
&_IO_file_jumps};
|
|
#else
|
|
# define DEF_STDFILE(NAME, FD, CHAIN, FLAGS) \
|
|
static struct _IO_wide_data _IO_wide_data_##FD \
|
|
= { ._wide_vtable = &_IO_wfile_jumps }; \
|
|
struct _IO_FILE_plus NAME \
|
|
= {FILEBUF_LITERAL(CHAIN, FLAGS, FD, &_IO_wide_data_##FD), \
|
|
&_IO_file_jumps};
|
|
#endif
|
|
|
|
DEF_STDFILE(_IO_2_1_stdin_, 0, 0, _IO_NO_WRITES);
|
|
DEF_STDFILE(_IO_2_1_stdout_, 1, &_IO_2_1_stdin_, _IO_NO_READS);
|
|
DEF_STDFILE(_IO_2_1_stderr_, 2, &_IO_2_1_stdout_, _IO_NO_READS+_IO_UNBUFFERED);
|
|
|
|
struct _IO_FILE_plus *_IO_list_all = &_IO_2_1_stderr_;
|
|
|
|
/* Finish double-linking stdin, stdout, and stderr in a constructor.
|
|
Static initialization cannot complete the _prevchain setup. */
|
|
|
|
__THROW __attribute__ ((constructor))
|
|
static void
|
|
_IO_stdfiles_init (void)
|
|
{
|
|
struct _IO_FILE **f;
|
|
for (f = (struct _IO_FILE **) &_IO_list_all;
|
|
*f != NULL;
|
|
f = &(*f)->_chain)
|
|
(*f)->_prevchain = f;
|
|
}
|
|
|
|
libc_hidden_data_def (_IO_list_all)
|