Analysis of the delayed execution mechanism of Golang functions

Golang is a widely used programming language that performs well in high-concurrency scenarios. One of its important features is the delayed execution mechanism of functions. This article will deeply explore the delayed execution mechanism of Golang functions, including the principle of delayed execution, precautions when using, etc.

1. The principle of delayed execution

The delayed execution mechanism in Golang is implemented through the defer keyword. When a function contains a defer statement, execution of the function pointed to by the statement will be deferred until the function containing the defer statement returns. The delayed execution mechanism will execute all defer statements first-in-last-out before the function returns. That is to say, the statements deferred first will be executed later.

The following is a simple sample code:

func main() {
    defer fmt.Println("world")
    fmt.Println("hello")
}

The output result is:

hello
world

As you can see, the delayed execution mechanism causes "world" to be executed first, and then "hello" implement.

2. Usage scenarios of delayed execution

In addition to being used for simple statement execution sequence control, the delayed execution mechanism has many more practical application scenarios.

2.1 Resource closure

In Golang, some resources need to be closed in time after use, such as file reading and writing, database connections, network communications, etc. If these resources are not released in time, it will lead to resource waste or resource leakage, thus affecting the performance and stability of the program.

The defer statement can be used for resource closing operations, such as file closing operations:

func readFile(filepath string) ([]byte, error) {
    file, err := os.Open(filepath)
    if err != nil {
        return nil, err
    }
    defer file.Close()

    return ioutil.ReadAll(file)
}

In the above code, the file closing operation is placed in the defer statement, so that even if the file is read If an error occurs, the file will be closed promptly to avoid resource leakage.

2.2 Error handling

When an error occurs during function execution, we may need to perform some cleanup operations. The defer statement can perform cleaning operations before the function returns, while avoiding the use of complex conditional statements to determine the timing of cleaning.

The following is a sample code to control code interruption:

func do() {
    defer func() {
        if r := recover(); r != nil {
            fmt.Printf("recovered from %v
", r)
        }
    }()
    panic("unknown error")
}

In the above code, by putting the recover statement into the defer statement, the program can be resumed after executing the panic statement , and perform necessary cleanup operations to avoid resource leakage caused by abnormal exit of the program.

2.3 Logging

In development, we often need to record some operation logs. Since logging operations are usually cumbersome and time-consuming, we can use the defer statement to perform logging operations while ensuring that logging is performed before the function returns.

The following is a sample code for recording function execution time:

func do() {
    defer func(start time.Time) {
        fmt.Printf("function cost %v
", time.Since(start))
    }(time.Now())

    // some code...
}

In the above code, we put the logging operations that need to be performed before the function returns into the defer statement. And use an anonymous function to pass in the timestamp as a parameter to obtain the function execution time.

3. Notes on delayed execution

Although the defer statement is very convenient, you need to pay attention to some things when using it, otherwise it will cause unnecessary trouble.

3.1 Delayed execution of function parameters

When the function parameters of the defer statement are function calls, you need to pay attention to when the parameters of the function are calculated. As shown in the following code:

func foo(i int) {
    fmt.Printf("foo(%d)
", i)
}

func bar() {
    i := 0
    defer foo(i)
    i++
}

The output result is:

foo(0)

As you can see, in the above code, the value of i is not calculated when the function returns, but when the defer statement is executed. derived. Therefore, you should be aware of this delayed evaluation when the function parameter is a reference to a variable.

3.2 Performance impact of delayed execution

Although the defer statement is convenient, it will also have an impact on the performance of the program when used in large quantities. Since the defer statement needs to push the function call parameters onto the stack, when a large number of delayed functions need to be executed, it will cause the stack memory to grow, thus affecting the performance of the program.

4. Summary

The delayed execution mechanism is one of the important features in the Golang language. It can be used for resource closure, error handling, logging and other operations. When using it, you need to pay attention to avoid the impact of delayed calculation and multiple calls to avoid unnecessary performance losses.

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