In this part, we will show methods of exchanging data between threads. In the example from the previous part, threads were defined using K_THREAD_DEFINE()macro.

K_THREAD_DEFINE(thread0_id, STACKSIZE, thread0, NULL, NULL, NULL,
		THREAD0_PRIORITY, 0, 0);

The arguments of the macro are:

• the name of the thread
• size of the stack that is created for individual use of the thread
• address of the function of the thread
• three initial arguments of the thread which can be passed at the start of the thread (here all NULL)
• constant that specifies the priority of the thread
• thread options (here 0)
• delay to start the thread (0 meaning no delay)

As we can see every thread has its own stack, which means that if there is a need to exchange data between threads we have to use some shared variable visible for all threads interested in using it. In multitasking environments, especially running on a multi-core processor, there is a need to synchronise the access to shared resources. Zephyr offers some mechanisms for inter-thread data exchange and synchronisation.