746c59c82a
Up until now, the `__thread` keyword has been used for declaring variables as Thread local storage. However, `__thread` is a GNU specific keyword which thus limits compatibility with other toolchains (for instance IAR). This PR intoduces a new macro `Z_THREAD_LOCAL` which expands to the corresponding C11, C23 or C++11 standard keyword based on the standard that is specified during compilation, else it uses the old `__thread` keyword. Signed-off-by: Daniel Flodin <daniel.flodin@iar.com>
59 lines
1.7 KiB
ReStructuredText
59 lines
1.7 KiB
ReStructuredText
.. _thread_local_storage:
|
|
|
|
Thread Local Storage (TLS)
|
|
##########################
|
|
|
|
Thread Local Storage (TLS) allows variables to be allocated on a per-thread
|
|
basis. These variables are stored in the thread stack which means every
|
|
thread has its own copy of these variables.
|
|
|
|
Zephyr currently requires toolchain support for TLS.
|
|
|
|
|
|
Configuration
|
|
*************
|
|
|
|
To enable thread local storage in Zephyr, :kconfig:option:`CONFIG_THREAD_LOCAL_STORAGE`
|
|
needs to be enabled. Note that this option may not be available if
|
|
the architecture or the SoC does not have the hidden option
|
|
:kconfig:option:`CONFIG_ARCH_HAS_THREAD_LOCAL_STORAGE` enabled, which means
|
|
the architecture or the SoC does not have the necessary code to support
|
|
thread local storage and/or the toolchain does not support TLS.
|
|
|
|
:kconfig:option:`CONFIG_ERRNO_IN_TLS` can be enabled together with
|
|
:kconfig:option:`CONFIG_ERRNO` to let the variable ``errno`` be a thread local
|
|
variable. This allows user threads to access the value of ``errno`` without
|
|
making a system call.
|
|
|
|
|
|
Declaring and Using Thread Local Variables
|
|
******************************************
|
|
|
|
The macro ``Z_THREAD_LOCAL`` can be used to declare thread local variables.
|
|
|
|
For example, to declare a thread local variable in header files:
|
|
|
|
.. code-block:: c
|
|
|
|
extern Z_THREAD_LOCAL int i;
|
|
|
|
And to declare the actual variable in source files:
|
|
|
|
.. code-block:: c
|
|
|
|
Z_THREAD_LOCAL int i;
|
|
|
|
Keyword ``static`` can also be used to limit the variable within a source file:
|
|
|
|
.. code-block:: c
|
|
|
|
static Z_THREAD_LOCAL int j;
|
|
|
|
Using the thread local variable is the same as using other variable, for example:
|
|
|
|
.. code-block:: c
|
|
|
|
void testing(void) {
|
|
i = 10;
|
|
}
|