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Paul Eggert
87fb310b69
In documentation and comments, be more like POSIX in terminology involving multithreading. Explain the distinction between multithreaded process vs multithreaded program. Change “program” to “process” when the latter wording is more accurate or informative. Simplify the wording for the constraints on processes that use unlocked I/O. Change “multithread-safe” to “thread-safe”. Change “thread-safety” to “thread safety”. However, do not change “multithreaded” to “multi-threaded” even though there are some uses of both spellinga, as there are a whole bunch of uses of “multithreaded”, also in identifier names; perhaps Gnulib should even standardize on “multithreaded” (not “multi-threaded”), contra POSIX.
64 lines
2.0 KiB
C
64 lines
2.0 KiB
C
/* replacement pread function
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Copyright (C) 2009-2026 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file 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
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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/* Specification. */
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#include <unistd.h>
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#include <errno.h>
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#define __libc_lseek(f,o,w) lseek (f, o, w)
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#define __set_errno(Val) errno = (Val)
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#define __libc_read(f,b,n) read (f, b, n)
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/* pread substitute for systems that the function, such as mingw32 and BeOS. */
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/* The following is identical to the function from glibc's
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sysdeps/posix/pread.c */
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/* Note: This implementation of pread is not thread-safe. */
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ssize_t
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pread (int fd, void *buf, size_t nbyte, off_t offset)
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{
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/* Since we must not change the file pointer preserve the value so that
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we can restore it later. */
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off_t old_offset = __libc_lseek (fd, 0, SEEK_CUR);
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if (old_offset == (off_t) -1)
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return -1;
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/* Set to wanted position. */
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if (__libc_lseek (fd, offset, SEEK_SET) == (off_t) -1)
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return -1;
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/* Write out the data. */
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ssize_t result = __libc_read (fd, buf, nbyte);
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/* Now we have to restore the position. If this fails we have to
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return this as an error. But if the writing also failed we
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return this error. */
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int saved_errno = errno;
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if (__libc_lseek (fd, old_offset, SEEK_SET) == (off_t) -1)
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{
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if (result == -1)
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__set_errno (saved_errno);
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return -1;
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}
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__set_errno (saved_errno);
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return result;
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}
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