https://devzone.nordicsemi.com/f/nordic-q-a/81847/racing-adventure-in-osHi,Master: Question 1: As shown in the below, why does the api read this variable with critical protection? Question 2: Suppose two tasks have write operations to shared variables. For example: In the OS source code, you can see thaten-USTelligent Community 13Thu, 18 Nov 2021 12:19:18 GMThttps://devzone.nordicsemi.com/thread/339627?ContentTypeID=1Thu, 18 Nov 2021 12:19:18 GMT137ad170-7792-4731-bb38-c0d22fbe4515:c4db6ad0-65e2-4146-abf9-b1576597ed8bEinar Thorsrud<p>Hi,</p> <p>Regarding Q1, I do not know where this code comes from so I cannot comment on why this is done like it is.</p> <p>Regarding Q2, you are right that as this is a pure write (no read-modify-write) there is no need for a critical section here, even if the same variable is written to by two tasks. I cannot see that it serves any purpose. (The variable should be <code>volatile</code> though (assuming it is also read somewhere), so that the compiler does not optimize away reading of the variable, thinking it know what it is set to.)</p> <p>Regarding Q3, there are some situations where you want to use the DSB/ISB instruction but I do not see any particular reason you would need that here (there is no context here, though).</p><div style="clear:both;"></div>