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<title>The GNU Fortran Compiler: Thread-safety of the runtime library</title>
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<a name="Thread_002dsafety-of-the-runtime-library"></a>
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<p>
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Next: <a href="Data-consistency-and-durability.html#Data-consistency-and-durability" accesskey="n" rel="next">Data consistency and durability</a>, Previous: <a href="Internal-representation-of-LOGICAL-variables.html#Internal-representation-of-LOGICAL-variables" accesskey="p" rel="prev">Internal representation of LOGICAL variables</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>
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<a name="Thread_002dsafety-of-the-runtime-library-1"></a>
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<h3 class="section">5.3 Thread-safety of the runtime library</h3>
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<a name="index-thread_002dsafety_002c-threads"></a>
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<p>GNU Fortran can be used in programs with multiple threads, e.g. by
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using OpenMP, by calling OS thread handling functions via the
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<code>ISO_C_BINDING</code> facility, or by GNU Fortran compiled library code
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being called from a multi-threaded program.
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</p>
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<p>The GNU Fortran runtime library, (<code>libgfortran</code>), supports being
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called concurrently from multiple threads with the following
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exceptions.
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</p>
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<p>During library initialization, the C <code>getenv</code> function is used,
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which need not be thread-safe. Similarly, the <code>getenv</code>
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function is used to implement the <code>GET_ENVIRONMENT_VARIABLE</code> and
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<code>GETENV</code> intrinsics. It is the responsibility of the user to
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ensure that the environment is not being updated concurrently when any
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of these actions are taking place.
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</p>
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<p>The <code>EXECUTE_COMMAND_LINE</code> and <code>SYSTEM</code> intrinsics are
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implemented with the <code>system</code> function, which need not be
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thread-safe. It is the responsibility of the user to ensure that
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<code>system</code> is not called concurrently.
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</p>
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<p>For platforms not supporting thread-safe POSIX functions, further
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functionality might not be thread-safe. For details, please consult
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the documentation for your operating system.
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</p>
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<p>The GNU Fortran runtime library uses various C library functions that
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depend on the locale, such as <code>strtod</code> and <code>snprintf</code>. In
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order to work correctly in locale-aware programs that set the locale
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using <code>setlocale</code>, the locale is reset to the default “C”
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locale while executing a formatted <code>READ</code> or <code>WRITE</code>
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statement. On targets supporting the POSIX 2008 per-thread locale
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functions (e.g. <code>newlocale</code>, <code>uselocale</code>,
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<code>freelocale</code>), these are used and thus the global locale set
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using <code>setlocale</code> or the per-thread locales in other threads are
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not affected. However, on targets lacking this functionality, the
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global LC_NUMERIC locale is set to “C” during the formatted I/O.
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Thus, on such targets it’s not safe to call <code>setlocale</code>
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concurrently from another thread while a Fortran formatted I/O
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operation is in progress. Also, other threads doing something
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dependent on the LC_NUMERIC locale might not work correctly if a
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formatted I/O operation is in progress in another thread.
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</p>
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<p>
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Next: <a href="Data-consistency-and-durability.html#Data-consistency-and-durability" accesskey="n" rel="next">Data consistency and durability</a>, Previous: <a href="Internal-representation-of-LOGICAL-variables.html#Internal-representation-of-LOGICAL-variables" accesskey="p" rel="prev">Internal representation of LOGICAL variables</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>
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