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177 lines
7.6 KiB
HTML
177 lines
7.6 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Reentrancy (The Red Hat newlib C Library)</title>
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<meta name="description" content="Reentrancy (The Red Hat newlib C Library)">
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<meta name="keywords" content="Reentrancy (The Red Hat newlib C Library)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="Misc.html#Misc" rel="next" title="Misc">
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<link href="setlocale.html#setlocale" rel="prev" title="setlocale">
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<style type="text/css">
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</style>
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</head>
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<body lang="en">
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<a name="Reentrancy"></a>
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<div class="header">
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<p>
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Next: <a href="Misc.html#Misc" accesskey="n" rel="next">Misc</a>, Previous: <a href="Locale.html#Locale" accesskey="p" rel="prev">Locale</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Reentrancy-1"></a>
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<h2 class="chapter">10 Reentrancy</h2>
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<a name="index-reentrancy"></a>
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<p>Reentrancy is a characteristic of library functions which allows multiple
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processes to use the same address space with assurance that the values stored
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in those spaces will remain constant between calls. The Red Hat
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newlib implementation of the library functions ensures that
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whenever possible, these library functions are reentrant. However,
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there are some functions that can not be trivially made reentrant.
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Hooks have been provided to allow you to use these functions in a fully
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reentrant fashion.
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</p>
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<a name="index-_005freent"></a>
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<a name="index-reent_002eh"></a>
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<a name="index-reentrancy-structure"></a>
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<p>These hooks use the structure <code>_reent</code> defined in <samp>reent.h</samp>.
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A variable defined as ‘<samp>struct _reent</samp>’ is called a <em>reentrancy
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structure</em>. All functions which must manipulate global information are
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available in two versions. The first version has the usual name, and
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uses a single global instance of the reentrancy structure. The second
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has a different name, normally formed by prepending ‘<samp>_</samp>’ and
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appending ‘<samp>_r</samp>’, and takes a pointer to the particular reentrancy
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structure to use.
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</p>
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<p>For example, the function <code>fopen</code> takes two arguments, <var>file</var>
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and <var>mode</var>, and uses the global reentrancy structure. The function
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<code>_fopen_r</code> takes the arguments, <var>struct_reent</var>, which is a
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pointer to an instance of the reentrancy structure, <var>file</var>
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and <var>mode</var>.
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</p>
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<p>There are two versions of ‘<samp>struct _reent</samp>’, a normal one and one
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for small memory systems, controlled by the <code>_REENT_SMALL</code>
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definition from the (automatically included) <samp><sys/config.h></samp>.
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</p>
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<a name="index-global-reentrancy-structure"></a>
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<a name="index-_005fimpure_005fptr"></a>
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<p>Each function which uses the global reentrancy structure uses the global
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variable <code>_impure_ptr</code>, which points to a reentrancy structure.
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</p>
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<p>This means that you have two ways to achieve reentrancy. Both require
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that each thread of execution control initialize a unique global
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variable of type ‘<samp>struct _reent</samp>’:
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</p>
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<ol>
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<li> <a name="index-extra-argument_002c-reentrant-fns"></a>
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Use the reentrant versions of the library functions, after initializing
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a global reentrancy structure for each process. Use the pointer to this
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structure as the extra argument for all library functions.
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</li><li> Ensure that each thread of execution control has a pointer to its own
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unique reentrancy structure in the global variable <code>_impure_ptr</code>,
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and call the standard library subroutines.
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</li></ol>
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<a name="index-list-of-reentrant-functions"></a>
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<a name="index-reentrant-function-list"></a>
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<p>The following functions are provided in both reentrant
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and non-reentrant versions.
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</p>
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<div class="example">
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<pre class="example"><em>Equivalent for errno variable:</em>
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</pre><pre class="example">_errno_r
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</pre><pre class="example"><em>Locale functions:</em>
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</pre><pre class="example">_localeconv_r _setlocale_r
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</pre><pre class="example"><em>Equivalents for stdio variables:</em>
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</pre><pre class="example">_stdin_r _stdout_r _stderr_r
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</pre><pre class="example"><em>Stdio functions:</em>
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</pre><pre class="example">_fdopen_r _perror_r _tempnam_r
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_fopen_r _putchar_r _tmpnam_r
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_getchar_r _puts_r _tmpfile_r
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_gets_r _remove_r _vfprintf_r
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_iprintf_r _rename_r _vsnprintf_r
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_mkstemp_r _snprintf_r _vsprintf_r
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_mktemp_t _sprintf_r
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</pre><pre class="example"><em>Signal functions:</em>
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</pre><pre class="example">_init_signal_r _signal_r
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_kill_r __sigtramp_r
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_raise_r
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</pre><pre class="example"><em>Stdlib functions:</em>
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</pre><pre class="example">_calloc_r _mblen_r _setenv_r
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_dtoa_r _mbstowcs_r _srand_r
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_free_r _mbtowc_r _strtod_r
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_getenv_r _memalign_r _strtol_r
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_mallinfo_r _mstats_r _strtoul_r
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_malloc_r _putenv_r _system_r
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_malloc_r _rand_r _wcstombs_r
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_malloc_stats_r _realloc_r _wctomb_r
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</pre><pre class="example"><em>String functions:</em>
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</pre><pre class="example">_strdup_r _strtok_r
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</pre><pre class="example"><em>System functions:</em>
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</pre><pre class="example">_close_r _link_r _unlink_r
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_execve_r _lseek_r _wait_r
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_fcntl_r _open_r _write_r
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_fork_r _read_r
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_fstat_r _sbrk_r
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_gettimeofday_r _stat_r
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_getpid_r _times_r
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</pre><pre class="example"><em>Time function:</em>
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</pre><pre class="example">_asctime_r
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</pre></div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Misc.html#Misc" accesskey="n" rel="next">Misc</a>, Previous: <a href="Locale.html#Locale" accesskey="p" rel="prev">Locale</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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