Test example・Simultaneous execution test of multiple functions

13/09/202121/10/2021Test qualityy

In embedded systems, it is also important to detect bugs hidden in the simultaneous execution of multiple processes.

In order for embedded software to continue to operate stably, it is important to identify and fix as many potential bugs as possible before release . Therefore, after the dynamic memory and resource leak test, timer and counter rollover test, let’s perform simultaneous execution test of multiple functions .

Simultaneous execution of multiple functions occurs at any time

There are various functions implemented in embedded software. And for each function, the test named normal system / quasi-normal system / abnormal system has confirmed the operation and stability of the single function . Built-in software only to run one by one function if, I may only test this single function, in the actual embedded software multiple functions are performed concurrently there that may be Ru.

For example, many embedded software devices have an interface, such as a GUI, that starts processing in response to instructions from the operator . In the case of such a device, the normal internal function as embedded software often operates behind the function execution in response to the instruction from the GUI . Then, when the timing of the operator’s screen operation by the GUI and the timing of the execution of the internal function match , the processing to execute the two functions is executed in parallel in the embedded software.

In this way, when the execution timing of the automatically executed internal function and the function executed by the operator’s instruction match, there are many patterns in which the processes that execute the two functions are executed at the same time in the embedded software. In addition, some embedded software has a function (multi-user / multitasking function) that executes processing from multiple users in parallel at the same time . In this case, if two users instruct the execution of some function at the same timing, the processing to execute the two functions will be executed at the same time.

Why bugs are likely to be latent in simultaneous execution of multiple processes

Even if two functions are executed at the same time, there is no problem if each function finishes operating normally . However, it is often the case that latent bugs move when two functions are executed at the same time . The most common is writing down data by accessing the same data at the same time , and reading inconsistent data in the middle of change . Both occur when there is a bug in exclusive control when multiple functions or processes access the same data .

For example, suppose you have information about sales to Mr. A, who has two data structures , product name and quantity . Suppose function A writes the information of 3 apples entered from the GUI now , and function B receives the information of 1 orange entered by Mr. A yesterday on another page from the communication line and writes it. If exclusive control is properly performed, two types of information, one orange and three apples, will be recorded in the sales contents for Mr. A.

In not been able to exclusive control , the bad timing I think what happens when the function A and function B is executed. Immediately after function A writes apple, function B receives communication and activates interrupt processing, writes one mandarin orange, and then function A returns and writes three. .. Then, as a result, Mr. A’s sales will be strange with 3 oranges.

The bug hidden in such exclusive control becomes apparent only when two functions are executed at the timing of writing data to the data at the same time . No matter how much you test on its own, you won’t find any potential bugs that depend on the timing of simultaneous execution of multiple features like this. This is just an example, but finding such potential bugs requires concurrent testing of multiple features .