TAILIEUCHUNG - Program C Ansi Programming Embedded Systems in C and C++ phần 7

Tham khảo tài liệu 'program c ansi programming embedded systems in c and c++ phần 7', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | else The mutex is taken. Add the calling task to the waiting list. pCallingTask pCallingTask- state Waiting pCallingTask pCallingTask Scheduling Point When the mutex is released the caller begins executing here. exitCS Critical Section End take The neatest thing about the take method is that if the mutex is currently held by another task that is the binary flag is already set the calling task will be suspended until the mutex is released by that other task. This is kind of like telling your spouse that you are going to take a nap and asking him or her to wake you up when dinner is ready. It is even possible for multiple tasks to be waiting for the same mutex. In fact the waiting list associated with each mutex is ordered by priority so the highest-priority waiting task will always be awakened first. The method that comes next is used to release a mutex. Although this method could be called by any task it is expected that only a task that previously called take would invoke it. Unlike take this routine will never block. However one possible result of releasing the mutex could be to wake a task of higher priority. In that case the releasing task would immediately be forced by the scheduler to give up control of the processor in favor of the higher-priority task. Method release Description Release a mutex that is held by the calling task. Notes Returns None defined. void Mutex release void Task pWaitingTask enterCS Critical Section Begins if state Held pWaitingTask if pWaitingTask NULL Wake the first task on the waiting list. pWaitingTask- pNext pWaitingTask- state Ready pWaitingTask Scheduling Point else state Available exitCS Critical Section End release Critical sections The primary use of mutexes is for the protection of shared resources. Shared resources are global variables memory buffers or device registers that are .

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