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| <section id="thread-local-storage"> |
| <h1>Thread Local Storage<a class="headerlink" href="#thread-local-storage" title="Permalink to this heading"></a></h1> |
| <p>Thread local storage (TLS) is a mechanism that allows each thread to have its own |
| copy of a variable. This is useful for variables that are used by multiple |
| functions in a thread, but should not be shared with other threads.</p> |
| <p>There are some approaches to using TLS in NuttX:</p> |
| <p>1. Use the <code class="docutils literal notranslate"><span class="pre">pthread_key_create()</span></code> and <code class="docutils literal notranslate"><span class="pre">pthread_setspecific()</span></code> that from the POSIX standard. This is the most portable approach, but it requires that |
| the platform support pthreads. |
| 2. Use the <code class="docutils literal notranslate"><span class="pre">thread_local</span></code> or <code class="docutils literal notranslate"><span class="pre">__thread</span></code> keyword from the C standard: <a class="reference external" href="https://gcc.gnu.org/onlinedocs/gcc/extensions-to-the-c-language-family/thread-local-storage.html">https://gcc.gnu.org/onlinedocs/gcc/extensions-to-the-c-language-family/thread-local-storage.html</a></p> |
| <section id="configuration"> |
| <h2>Configuration<a class="headerlink" href="#configuration" title="Permalink to this heading"></a></h2> |
| <div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="go">CONFIG_SCHED_THREAD_LOCAL /* Enable native thread local storage support */</span> |
| </pre></div> |
| </div> |
| <p>Enable it to support native thread local storage, which is required that the compiler configured with <code class="docutils literal notranslate"><span class="pre">--enable-tls</span></code> option, this approach is more efficient if the compiler support it.</p> |
| <p>If your compiler support it then you still need further configuration to use it:</p> |
| <ol class="arabic simple"> |
| <li><p>Enable <code class="docutils literal notranslate"><span class="pre">CONFIG_SCHED_THREAD_LOCAL</span></code> in menuconfig</p></li> |
| <li><p>Handle <code class="docutils literal notranslate"><span class="pre">tbss</span></code> and <code class="docutils literal notranslate"><span class="pre">tdata</span></code> sections in linker script, your can refer to the example in rv-virt</p></li> |
| </ol> |
| <p>To confirm that your compiler supports TLS, you can try this command:</p> |
| <div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="go">arm-none-eabi-gcc --verbose</span> |
| <span class="go">COLLECT_GCC=arm-none-eabi-gcc</span> |
| <span class="go">COLLECT_LTO_WRAPPER=/home/huang/.local/pkg/arm/bin/../libexec/gcc/arm-none-eabi/13.3.1/lto-wrapper</span> |
| <span class="go">Target: arm-none-eabi</span> |
| <span class="go">Configured with: /data/jenkins/workspace/GNU-toolchain/arm-13/src/gcc/configure --target=arm-none-eabi --prefix=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/install --with-gmp=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/host-tools --with-mpfr=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/host-tools --with-mpc=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/host-tools --with-isl=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/host-tools --disable-shared --disable-nls --disable-threads --disable-tls --enable-checking=release --enable-languages=c,c++,fortran --with-newlib --with-gnu-as --with-headers=yes --with-gnu-ld --with-native-system-header-dir=/include --with-sysroot=/data/jenkins/workspace/GNU-toolchain/arm-13/build-arm-none-eabi/install/arm-none-eabi --with-multilib-list=aprofile,rmprofile --with-pkgversion='Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24)' --with-bugurl=https://bugs.linaro.org/</span> |
| <span class="go">Thread model: single</span> |
| <span class="go">Supported LTO compression algorithms: zlib</span> |
| <span class="go">gcc version 13.3.1 20240614 (Arm GNU Toolchain 13.3.Rel1 (Build arm-13.24))</span> |
| </pre></div> |
| </div> |
| <p>Then you can see <code class="docutils literal notranslate"><span class="pre">--disable-tls</span></code> in the output, which means that your compiler does not support TLS.</p> |
| <p>In this case, you can still use the thread local relative keyword, but it would be implemented by libgcc’s emutls.</p> |
| </section> |
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