59 lines
1.6 KiB
ReStructuredText
59 lines
1.6 KiB
ReStructuredText
.. _thread_local_storage:
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Thread Local Storage (TLS)
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##########################
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Thread Local Storage (TLS) allows variables to be allocated on a per-thread
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basis. These variables are stored in the thread stack which means every
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thread has its own copy of these variables.
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Zephyr currently requires toolchain support for TLS.
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Configuration
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*************
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To enable thread local storage in Zephyr, :kconfig:option:`CONFIG_THREAD_LOCAL_STORAGE`
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needs to be enabled. Note that this option may not be available if
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the architecture or the SoC does not have the hidden option
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:kconfig:option:`CONFIG_ARCH_HAS_THREAD_LOCAL_STORAGE` enabled, which means
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the architecture or the SoC does not have the necessary code to support
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thread local storage and/or the toolchain does not support TLS.
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:kconfig:option:`CONFIG_ERRNO_IN_TLS` can be enabled together with
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:kconfig:option:`CONFIG_ERRNO` to let the variable ``errno`` be a thread local
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variable. This allows user threads to access the value of ``errno`` without
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making a system call.
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Declaring and Using Thread Local Variables
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******************************************
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The keyword ``__thread`` can be used to declare thread local variables.
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For example, to declare a thread local variable in header files:
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.. code-block:: c
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extern __thread int i;
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And to declare the actual variable in source files:
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.. code-block:: c
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__thread int i;
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Keyword ``static`` can also be used to limit the variable within a source file:
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.. code-block:: c
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static __thread int j;
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Using the thread local variable is the same as using other variable, for example:
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.. code-block:: c
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void testing(void) {
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i = 10;
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}
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