golang panic usage

Golang is an efficient, concurrent and concise development language with good readability and maintainability. However, sometimes even in such a language, unexpected errors occur in the code, such as: array out of bounds, null pointer, or even system crash, etc. In order to deal with these problems, Go provides a simple processing method: panic.

1. What is panic?
Panic is a built-in function used to indicate that an unrecoverable error has occurred in the program. When the panic function is called, the program stops the current flow and throws an error, then stops running and ends the call stack.

2. How to use panic?
Panic is easy to use. Just throw the error directly through the panic() function. For example:

func app() {
    if err := someFunction(); err != nil{
        log.Printf("operation failed, error - %s", err.Error())
        panic(err)
    }
    // 其他代码
}

If an error occurs in someFunction(), the application will stop running and throw a panic err error message.

In the above example code, when an error occurs in the function, we print the details of the error and pass it to the panic function. This will cause the program to force stop and print an error message on the console. In this case, specific error information will be printed, and the application will stop running and will not continue to execute subsequent code. At this time, an error catching mechanism needs to be introduced into the code to ensure the correctness of the application.

3. The relationship between panic and Recover

If panic is used in the code, all the code in the call stack will stop running, the program will stop and an error message will be output, which will have a negative impact on the program. Have a great impact. Therefore, in the Go language, the paired use of panic and recover can make the program more robust.

The panic function will only stop the running of the program in the function that directly calls it. Then on the call stack of the function, when the exception reaches the top of the call stack, it will end the running of the program.

recover has the ability to restore system operation, it can only be called in the delay function. The function of recover is to intercept panic exceptions and restore system operation.

If there is no panic before calling the recover function, then recover will not do anything.

Let’s look at the following example:

func recoverDemo() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("recover from panic", r)
        }
    }()

    panic("something wrong")
    fmt.Println("After panic")
}

In this example, the function after the defer keyword will be executed before the function ends. If a panic occurs during function execution, the recover method will be activated after reaching the defer expression. It will catch the panic and print out the message we pass it.

In Golang, recover is usually used to recover from panic. Usually, during the development process, we hope that the program will not stop under certain circumstances, even if an exception occurs in the function, which requires us to use the recover function to recover.

4. Best Practices

In order to avoid program crashes caused by calling panic, we should try our best to catch these exceptions and use recover to recover when appropriate. In my practice, I usually follow the following principles when using panic:

1. Keep it simple
panic should not be abused in code and should only be used when a truly unrecoverable error occurs. In other cases, error handling mechanisms should be used.

2. Use the defer function correctly
We usually use the defer function to handle the cleanup of resource usage. However, when using panic and recover, the location of defer execution is very important. Call recover in the defer function to capture and handle panic exceptions.

3. Use standard error
The standard error mechanism in Golang is very useful. If an error occurs, we should use an error type variable to pass error information, and determine whether an error occurs by determining whether the variable is nil.

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