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diff --git a/share/doc/gfortran/Data-consistency-and-durability.html b/share/doc/gfortran/Data-consistency-and-durability.html new file mode 100644 index 0000000..91178e6 --- /dev/null +++ b/share/doc/gfortran/Data-consistency-and-durability.html @@ -0,0 +1,160 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1999-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>The GNU Fortran Compiler: Data consistency and durability</title> + +<meta name="description" content="The GNU Fortran Compiler: Data consistency and durability"> +<meta name="keywords" content="The GNU Fortran Compiler: Data consistency and durability"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Compiler-Characteristics.html#Compiler-Characteristics" rel="up" title="Compiler Characteristics"> +<link href="Files-opened-without-an-explicit-ACTION_003d-specifier.html#Files-opened-without-an-explicit-ACTION_003d-specifier" rel="next" title="Files opened without an explicit ACTION= specifier"> +<link href="Thread_002dsafety-of-the-runtime-library.html#Thread_002dsafety-of-the-runtime-library" rel="previous" title="Thread-safety of the runtime library"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Data-consistency-and-durability"></a> +<div class="header"> +<p> +Next: <a href="Files-opened-without-an-explicit-ACTION_003d-specifier.html#Files-opened-without-an-explicit-ACTION_003d-specifier" accesskey="n" rel="next">Files opened without an explicit ACTION= specifier</a>, Previous: <a href="Thread_002dsafety-of-the-runtime-library.html#Thread_002dsafety-of-the-runtime-library" accesskey="p" rel="previous">Thread-safety of the runtime library</a>, Up: <a href="Compiler-Characteristics.html#Compiler-Characteristics" accesskey="u" rel="up">Compiler Characteristics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Data-consistency-and-durability-1"></a> +<h3 class="section">4.6 Data consistency and durability</h3> +<a name="index-consistency_002c-durability"></a> + +<p>This section contains a brief overview of data and metadata +consistency and durability issues when doing I/O. +</p> +<p>With respect to durability, GNU Fortran makes no effort to ensure that +data is committed to stable storage. If this is required, the GNU +Fortran programmer can use the intrinsic <code>FNUM</code> to retrieve the +low level file descriptor corresponding to an open Fortran unit. Then, +using e.g. the <code>ISO_C_BINDING</code> feature, one can call the +underlying system call to flush dirty data to stable storage, such as +<code>fsync</code> on POSIX, <code>_commit</code> on MingW, or <code>fcntl(fd, +F_FULLSYNC, 0)</code> on Mac OS X. The following example shows how to call +fsync: +</p> +<div class="smallexample"> +<pre class="smallexample"> ! Declare the interface for POSIX fsync function + interface + function fsync (fd) bind(c,name="fsync") + use iso_c_binding, only: c_int + integer(c_int), value :: fd + integer(c_int) :: fsync + end function fsync + end interface + + ! Variable declaration + integer :: ret + + ! Opening unit 10 + open (10,file="foo") + + ! ... + ! Perform I/O on unit 10 + ! ... + + ! Flush and sync + flush(10) + ret = fsync(fnum(10)) + + ! Handle possible error + if (ret /= 0) stop "Error calling FSYNC" +</pre></div> + +<p>With respect to consistency, for regular files GNU Fortran uses +buffered I/O in order to improve performance. This buffer is flushed +automatically when full and in some other situations, e.g. when +closing a unit. It can also be explicitly flushed with the +<code>FLUSH</code> statement. Also, the buffering can be turned off with the +<code>GFORTRAN_UNBUFFERED_ALL</code> and +<code>GFORTRAN_UNBUFFERED_PRECONNECTED</code> environment variables. Special +files, such as terminals and pipes, are always unbuffered. Sometimes, +however, further things may need to be done in order to allow other +processes to see data that GNU Fortran has written, as follows. +</p> +<p>The Windows platform supports a relaxed metadata consistency model, +where file metadata is written to the directory lazily. This means +that, for instance, the <code>dir</code> command can show a stale size for a +file. One can force a directory metadata update by closing the unit, +or by calling <code>_commit</code> on the file descriptor. Note, though, +that <code>_commit</code> will force all dirty data to stable storage, which +is often a very slow operation. +</p> +<p>The Network File System (NFS) implements a relaxed consistency model +called open-to-close consistency. Closing a file forces dirty data and +metadata to be flushed to the server, and opening a file forces the +client to contact the server in order to revalidate cached +data. <code>fsync</code> will also force a flush of dirty data and metadata +to the server. Similar to <code>open</code> and <code>close</code>, acquiring and +releasing <code>fcntl</code> file locks, if the server supports them, will +also force cache validation and flushing dirty data and metadata. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Files-opened-without-an-explicit-ACTION_003d-specifier.html#Files-opened-without-an-explicit-ACTION_003d-specifier" accesskey="n" rel="next">Files opened without an explicit ACTION= specifier</a>, Previous: <a href="Thread_002dsafety-of-the-runtime-library.html#Thread_002dsafety-of-the-runtime-library" accesskey="p" rel="previous">Thread-safety of the runtime library</a>, Up: <a href="Compiler-Characteristics.html#Compiler-Characteristics" accesskey="u" rel="up">Compiler Characteristics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |