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This article mainly introduces the example analysis of mutex semaphores in vxworks, which is very detailed and has certain reference value. Friends who are interested must finish it!

Multitasking systems are often faced with a problem: resource competition. What are the resources? Many, such as peripherals, files, data and so on. Conflicts occur when multiple tasks access these resources at the same time. For example, the following code

Each time the function myBufPut () is called, a character is stored in the array myBuf [], which is equivalent to a stack operation. In a real system, if there are too many tasks, anything can happen. If this function is called by two tasks (T1 and T2), the following execution sequence may appear.

No sooner had T1 added 1 to myBufIndex than it was preempted by the high-priority T2. Then you must wait for T2 to exit the ready queue before T1 can continue execution. The end result is that nothing is stored in myBuf [0], while myBuf [1] is first stored in 'baked' and then saved in'a'. It can be seen that with only two lines of code, something will go wrong. What if a resource has only one line of code?

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