Feedback

Thread life cycle

A thread is the basic unit of runnable code. The vast majority of firmware code will run in threads – whether it’s a user-defined thread, a thread created by the RTOS (for example a system workqueue thread), a thread created by an RTOS subsystem (for example a logger module), or a thread created by a library (for example the AT Monitor library).

A thread has the following items:

Thread control block: This is of type k_thread. For each thread, there will be an instance of a thread control block within the RTOS that keeps track of a thread’s information, specifically its metadata.
Stack: Each thread will have its own stack. The stack area’s size must be set to align with the specific processing requirements of the thread. The next section will cover how to set the right thread size.
Entry point function: This is the body of the thread or, in other words, the functionality implemented by it. It usually contains an infinite loop, as exiting the entry point will terminate the thread. The entry point function can have three optional argument values that can be passed to it on start.
Thread priority: The priority is just a signed integer that governs the “type” of the thread. It instructs the scheduler how to allocate CPU time to the thread. We will dive into this in the next topic, Scheduler in-depth.
Optional thread options: As covered in the nRF Connect SDK Fundamentals course – Lesson 7, by using this optional field, you can make the thread receive special treatment under specific circumstances.
Optional starting delay: You can instruct the kernel to immediately place the created thread in the queue of ready threads (ready queue) by passing K_NO_WAIT which is simply a start delay of 0. Or we can specify an optional start delay.

Creating a thread

Threads are created using either the K_THREAD_DEFINE() macro or the k_thread_create() function. In both cases, a stack needs to be allocated statically (dynamic threads are not supported in Zephyr RTOS as of v3.4.0). The K_THREAD_DEFINE() macro manages the stack allocation itself, and the desired stack size is passed as a parameter to the same macro. Conversely, if you use the k_thread_create() function, you must allocate a stack using the K_THREAD_STACK_DEFINE() macro in advance.

Recall

Recall from Lesson 7 – Multithreaded applications and Lesson 8 – Thread synchronization in the nRF Connect SDK Fundamentals course, when creating a thread, you can start it immediately or after specifying a certain delay. Once the thread is started, it is placed in the queue of ready threads (ready queue).

As was covered in the fundamentals course, when creating a thread, you can start it immediately or after specifying a certain delay. Once the thread is started, it is placed in the queue of ready threads (ready queue).

There is also the option to create a thread with the delay set to K_FOREVER, which effectively makes the thread inactive. To activate, call k_thread_start(), which will add the thread to the queue of ready threads (ready queue).

Definition

Ready queue: The queue of threads that has the state Ready. The scheduler only cares about the threads in the ready queue when deciding which one should be the current Running thread.

Thread states

If the scheduler picks up the thread for execution, its state transitions to Running. Scheduling policies are covered in the next topic, Scheduling in-depth. The thread will stay Running until:

The thread changes to an Unready state, meaning it has either the Sleeping, Suspended, or Waiting state.
- Sleeping: The thread decides to sleep for some time by calling k_sleep() or its derivatives.
- Suspended: Another thread suspends the thread by calling k_thread_suspend().
- Waiting: The thread waits for a kernel object (for example, a mutex or a semaphore) that is unavailable.

The thread yields on its own or is preempted by the scheduler.
- The thread yields by calling k_yield() to give up the CPU, and putting itself at the end of the ready queue.
- The thread is preempted by the scheduler in a rescheduling point when there is a higher priority thread in the ready queue. When preempted, the thread is placed at the end of the ready queue.

Terminate or abort

The thread execution ends by termination or aborting.
- A termination takes place when the entry point function of the thread is exited. This happens in a few situations where a thread has defined non-repetitive tasks, and it’s done with those tasks.
- Aborting can happen automatically if the thread encounters a fatal error condition, such as de-referencing a null pointer, in which case the RTOS aborts the thread. Alternatively, a thread can be deliberately aborted by another thread or by itself using the k_thread_abort() function.

More details on threads can be found on the Threads page of the nRF Connect SDK documentation.

Nordic Developer Academy Terms of Service

1. Introduction

‍These terms and conditions (“Terms of Use”) apply to the use of the Nordic Developer Academy, provided by Nordic Semiconductor ASA, org. nr. 966 011 726, a public limited liability company registered in Norway (“Nordic Semiconductor”). ‍

Nordic Developer Academy allows the user to take technical courses related to Nordic Semiconductor products, software and services, and obtain a certificate certifying completion of these courses. By completing the registration process for the Nordic Developer Academy, you are agreeing to be bound by these Terms of Use.

These Terms of Use are applicable as long as you have a user account giving you access to Nordic Developer Academy.‍

‍2. Access to and use of Nordic Developer Academy

‍‍Upon acceptance of these Terms of Use you are granted a non-exclusive right of access to, and use of Nordic Developer Academy, as it is provided to you at any time. Nordic Semiconductor provides Nordic Developer Academy to you free of charge, subject to the provisions of these Terms of Use and the Nordic Developer Academy Privacy Policy.

To access select features of Nordic Developer Academy, you need to create a user account. You are solely responsible for the security associated with your user account, including always keeping your login details safe.

You will able to receive an electronic certificate from Nordic Developer Academy upon completion of courses. By issuing you such a certificate, Nordic Semiconductor certifies that you have completed the applicable course, but does not provide any further warrants or endorsements for any particular skills or professional qualifications.

Nordic Semiconductor will continuously develop Nordic Developer Academy with new features and functionality, but reserves the right to remove or alter any existing functions without notice.

‍3. Acceptable use

You undertake that you will use Nordic Developer Academy in accordance with applicable law and regulations, and in accordance with these Terms of Use.‍ You must not modify, adapt, or hack Nordic Developer Academy or modify another website so as to falsely imply that it is associated with Nordic Developer Academy, Nordic Semiconductor, or any other Nordic Semiconductor product, software or service.

You agree not to reproduce, duplicate, copy, sell, resell or in any other way exploit any portion of Nordic Developer Academy, use of Nordic Developer Academy, or access to Nordic Developer Academy without the express written permission by Nordic Semiconductor. You must not upload, post, host, or transmit unsolicited email, SMS, or \”spam\” messages.

You are responsible for ensuring that the information you post and the content you share does not;

contain false, misleading or otherwise erroneous information
infringe someone else’s copyrights or other intellectual property rights
contain sensitive personal data or
contain information that might be received as offensive or insulting.
Such information may be removed without prior notice.

‍Nordic Semiconductor reserves the right to at any time determine whether a use of Nordic Developer Academy is in violation of its requirements for acceptable use.

Violation of the at any time applicable requirements for acceptable use may result in termination of your account. We will take reasonable steps to notify you and state the reason for termination in such cases.

‍4. Routines for planned maintenance

‍Certain types of maintenance may imply a stop or reduction in availability of Nordic Developer Academy. Nordic Semiconductor does not warrant any level of service availability but will provide its best effort to limit the impact of any planned maintenance on the availability of Nordic Developer Academy.

5. Intellectual property rights

‍Nordic Semiconductor retains all rights to all elements of Nordic Developer Academy. This includes, but is not limited to, the concept, design, trademarks, know-how, trade secrets, copyrights and all other intellectual property rights.

Nordic Semiconductor receives all rights to all content uploaded or created in Nordic Developer Academy. You do not receive any license or usage rights to Nordic Developer Academy beyond what is explicitly stated in this Agreement.

‍6. Liability and damages

‍Nothing within these Terms of Use is intended to limit your statutory data privacy rights as a data subject, as described in the Nordic Developer Academy Privacy Policy. ‍You acknowledge that errors might occur from time to time and waive any right to claim for compensation as a result of errors in Nordic Developer Academy. When an error occurs, you shall notify Nordic Semiconductor of the error and provide a description of the error situation.

You agree to indemnify Nordic Semiconductor for any loss, including indirect loss, arising out of or in connection with your use of Nordic Developer Academy or violations of these Terms of Use. ‍Nordic Semiconductor shall not be held liable for, and does not warrant that (i) Nordic Developer Academy will meet your specific requirements, (ii) Nordic Developer Academy will be uninterrupted, timely, secure, or error-free, (iii) the results that may be obtained from the use of Nordic Developer Academy will be accurate or reliable, (iv) the quality of any products, services, information, or other material purchased or obtained by you through Nordic Developer Academy will meet your expectations, or that (v) any errors in Nordic Developer Academy will be corrected.

You accept that this is a service provided to you without any payment and hence you accept that Nordic Semiconductor will not be held responsible, or liable, for any breaches of these Terms of Use or any loss connected to your use of Nordic Developer Academy. Unless otherwise follows from mandatory law, Nordic Semiconductor will not accept any such responsibility or liability.

‍7. Change of terms

‍Nordic Semiconductor may update and change the Terms of Use from time to time. Nordic Semiconductor will seek to notify you about significant changes before such changes come into force and give you a possibility to evaluate the effects of proposed changes. Continued use of Nordic Developer Academy after any such changes shall constitute your acceptance of such changes. You can review the current version of the Terms of Use at any time at https://academy.nordicsemi.com/terms-of-service/

‍8. Transfer of rights

‍Nordic Semiconductor is entitled to transfer its rights and obligation pursuant to these Terms of Use to a third party as part of a merger or acquisition process, or as a result of other organizational changes.

‍9. Third Party Services

‍‍To the extent Nordic Developer Academy facilitates access to services provided by a third party, you agree to comply with the terms governing such third party services. Nordic Semiconductor shall not be held liable for any errors, omissions, inaccuracies, etc. related to such third party services.

‍10. Dispute resolution

‍‍The Terms of Use and any other legally binding agreement between yourself and Nordic Semiconductor shall be subject to Norwegian law and Norwegian courts’ exclusive jurisdiction.

nRF Connect SDK Intermediate

Thread life cycle

Creating a thread

Recall

Definition

Thread states

Terminate or abort

Switch language?

Change summary

What's new in the latest version

General updates

Bluetooth LE updates

MCUboot & Partition Manager