Custom Data

A thread’s custom data is a 32-bit, thread-specific value that may be used by an application for any purpose.

Concepts

Every thread has a 32-bit custom data area. The custom data is accessible only by the thread itself, and may be used by the application for any purpose it chooses. The default custom data for a thread is zero.

Note

Custom data support is not available to ISRs because they operate within a single shared kernel interrupt handling context.

Implementation

Using Custom Data

By default, thread custom data support is disabled. The configuration option CONFIG_THREAD_CUSTOM_DATA can be used to enable support.

The k_thread_custom_data_set() and k_thread_custom_data_get() functions are used to write and read a thread’s custom data, respectively. A thread can only access its own custom data, and not that of another thread.

The following code uses the custom data feature to record the number of times each thread calls a specific routine.

Note

Obviously, only a single routine can use this technique, since it monopolizes the use of the custom data feature.

int call_tracking_routine(void)
{
    uint32_t call_count;

    if (k_is_in_isr()) {
        /* ignore any call made by an ISR */
    } else {
        call_count = (uint32_t)k_thread_custom_data_get();
        call_count++;
        k_thread_custom_data_set((void *)call_count);
    }

    /* do rest of routine's processing */
    ...
}

Suggested Uses

Use thread custom data to allow a routine to access thread-specific information, by using the custom data as a pointer to a data structure owned by the thread.

Configuration Options

Related configuration options:

• CONFIG_THREAD_CUSTOM_DATA

APIs

The following thread custom data APIs are provided by kernel.h:

• k_thread_custom_data_set()
• k_thread_custom_data_get()