Do Goroutines in Go\'s HTTP Handlers Always Complete After the Response?

Goroutine Execution in HTTP Handlers

In Go, HTTP handlers often perform asynchronous tasks using goroutines. However, it's unclear whether these goroutines will complete after the handler returns a response.

Consider the following code:

package main

import (
    "fmt"
    "net/http"
    "time"
)

func worker() {
    fmt.Println("worker started")
    time.Sleep(time.Second * 10)
    fmt.Println("worker completed")
}

func HomeHandler(w http.ResponseWriter, r *http.Request) {
    go worker()
    w.Write([]byte("Hello, World!"))
}

func main() {
    http.HandleFunc("/home", HomeHandler)
    http.ListenAndServe(":8081", nil)
}

Will the worker goroutine complete in all situations after the response is written to the client?

Answer:

The worker goroutine will complete in all normal cases. The only way to prevent it from completing is to exit the program (by returning from main() or encountering a fatal error), or to run out of memory.

In a typical HTTP request-response scenario, the handler function (in this case, HomeHandler) returns after writing the response to the client. However, the program does not exit immediately. The goroutine executing the worker function will continue running until it completes or encounters an error.

The main() function, which is responsible for starting the HTTP server, will continue running until the program exits. Therefore, the worker goroutine has ample time to complete its execution, regardless of when the response is sent to the client.

In conclusion, while it may seem counterintuitive at first, goroutines started within HTTP handlers will complete even after the response is returned, unless the program terminates abnormally or runs out of memory. This allows for asynchronous tasks to be performed without blocking the handler from sending the response.

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