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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.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>.
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As a special exception, if you link the code in this file with
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files compiled with a GNU compiler to produce an executable,
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that does not cause the resulting executable to be covered by
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the GNU Lesser General Public License. This exception does not
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however invalidate any other reasons why the executable file
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might be covered by the GNU Lesser General Public License.
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This exception applies to code released by its copyright holders
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in files containing the exception. */
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/* This file provides definitions of _IO_2_1_stdin_, _IO_2_1_stdout_,
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and _IO_2_1_stderr_, the default values of stdin, stdout, stderr.
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See oldstdfiles.c for glibc 2.0 legacy definitions without wide
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character support. */
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#include "libioP.h"
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#ifdef _IO_MTSAFE_IO
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# define DEF_STDFILE(NAME, FD, CHAIN, FLAGS) \
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static _IO_lock_t _IO_stdfile_##FD##_lock = _IO_lock_initializer; \
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static struct _IO_wide_data _IO_wide_data_##FD \
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= { ._wide_vtable = &_IO_wfile_jumps }; \
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struct _IO_FILE_plus NAME \
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= {FILEBUF_LITERAL(CHAIN, FLAGS, FD, &_IO_wide_data_##FD), \
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&_IO_file_jumps};
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#else
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# define DEF_STDFILE(NAME, FD, CHAIN, FLAGS) \
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static struct _IO_wide_data _IO_wide_data_##FD \
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= { ._wide_vtable = &_IO_wfile_jumps }; \
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struct _IO_FILE_plus NAME \
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= {FILEBUF_LITERAL(CHAIN, FLAGS, FD, &_IO_wide_data_##FD), \
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&_IO_file_jumps};
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#endif
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DEF_STDFILE(_IO_2_1_stdin_, 0, 0, _IO_NO_WRITES);
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DEF_STDFILE(_IO_2_1_stdout_, 1, &_IO_2_1_stdin_, _IO_NO_READS);
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DEF_STDFILE(_IO_2_1_stderr_, 2, &_IO_2_1_stdout_, _IO_NO_READS+_IO_UNBUFFERED);
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struct _IO_FILE_plus *_IO_list_all = &_IO_2_1_stderr_;
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/* Finish double-linking stdin, stdout, and stderr in a constructor.
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Static initialization cannot complete the _prevchain setup. */
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__THROW __attribute__ ((constructor))
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static void
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_IO_stdfiles_init (void)
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{
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struct _IO_FILE **f;
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for (f = (struct _IO_FILE **) &_IO_list_all;
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*f != NULL;
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f = &(*f)->_chain)
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(*f)->_prevchain = f;
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}
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libc_hidden_data_def (_IO_list_all)
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