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116 lines
5.1 KiB
HTML
116 lines
5.1 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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<!-- This manual describes how to install and use the GNU multiple precision
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arithmetic library, version 6.1.0.
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Copyright 1991, 1993-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document under
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the terms of the GNU Free Documentation License, Version 1.3 or any later
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version published by the Free Software Foundation; with no Invariant Sections,
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with the Front-Cover Texts being "A GNU Manual", and with the Back-Cover
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Texts being "You have freedom to copy and modify this GNU Manual, like GNU
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software". A copy of the license is included in
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GNU Free Documentation License. -->
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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 (GNU MP 6.1.0)</title>
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<meta name="description" content="How to install and use the GNU multiple precision arithmetic library, version 6.1.0.">
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<meta name="keywords" content="Reentrancy (GNU MP 6.1.0)">
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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=iso-8859-1">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="GMP-Basics.html#GMP-Basics" rel="up" title="GMP Basics">
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<link href="Useful-Macros-and-Constants.html#Useful-Macros-and-Constants" rel="next" title="Useful Macros and Constants">
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<link href="Memory-Management.html#Memory-Management" rel="prev" title="Memory Management">
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<style type="text/css">
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span.roman {font-family: initial; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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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="Useful-Macros-and-Constants.html#Useful-Macros-and-Constants" accesskey="n" rel="next">Useful Macros and Constants</a>, Previous: <a href="Memory-Management.html#Memory-Management" accesskey="p" rel="prev">Memory Management</a>, Up: <a href="GMP-Basics.html#GMP-Basics" accesskey="u" rel="up">GMP Basics</a> [<a href="Concept-Index.html#Concept-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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<h3 class="section">3.7 Reentrancy</h3>
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<a name="index-Reentrancy"></a>
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<a name="index-Thread-safety"></a>
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<a name="index-Multi_002dthreading"></a>
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<p>GMP is reentrant and thread-safe, with some exceptions:
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</p>
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<ul>
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<li> If configured with <samp>--enable-alloca=malloc-notreentrant</samp> (or with
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<samp>--enable-alloca=notreentrant</samp> when <code>alloca</code> is not available),
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then naturally GMP is not reentrant.
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</li><li> <code>mpf_set_default_prec</code> and <code>mpf_init</code> use a global variable for the
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selected precision. <code>mpf_init2</code> can be used instead, and in the C++
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interface an explicit precision to the <code>mpf_class</code> constructor.
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</li><li> <code>mpz_random</code> and the other old random number functions use a global
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random state and are hence not reentrant. The newer random number functions
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that accept a <code>gmp_randstate_t</code> parameter can be used instead.
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</li><li> <code>gmp_randinit</code> (obsolete) returns an error indication through a global
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variable, which is not thread safe. Applications are advised to use
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<code>gmp_randinit_default</code> or <code>gmp_randinit_lc_2exp</code> instead.
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</li><li> <code>mp_set_memory_functions</code> uses global variables to store the selected
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memory allocation functions.
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</li><li> If the memory allocation functions set by a call to
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<code>mp_set_memory_functions</code> (or <code>malloc</code> and friends by default) are
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not reentrant, then GMP will not be reentrant either.
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</li><li> If the standard I/O functions such as <code>fwrite</code> are not reentrant then the
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GMP I/O functions using them will not be reentrant either.
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</li><li> It’s safe for two threads to read from the same GMP variable simultaneously,
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but it’s not safe for one to read while another might be writing, nor for
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two threads to write simultaneously. It’s not safe for two threads to
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generate a random number from the same <code>gmp_randstate_t</code> simultaneously,
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since this involves an update of that variable.
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</li></ul>
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</body>
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</html>
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