Do Goroutines in HTTP Handlers Always Complete After the Response is Sent?

Goroutine Execution in an HTTP Handler

When using goroutines within an HTTP handler, it's natural to wonder about their completion status after returning the response. Let's explore the example code provided:

// Handler that starts a goroutine
func HomeHandler(w http.ResponseWriter, r *http.Request) {
    go worker() // Starts a goroutine called "worker"
    w.Write([]byte("Hello, World!")) // Sends a response to the client
}

The question arises: will the "worker" goroutine always complete, even after the HTTP response is sent?

The Answer

Yes, the "worker" goroutine will complete in all situations. Here's why:

Goroutines are lightweight threads that run concurrently with the main program. Starting a goroutine with go assigns it a stack and preempts it into execution. Once the goroutine is created, it runs independently of the main program, even after the current function (in this case, the HomeHandler) has returned.

In the provided example, the goroutine starts executing immediately after the go worker() line. It prints a message to indicate its start and then sleeps for 10 seconds before printing a completion message.

While the goroutine is running, the HomeHandler function continues execution and sends the response to the client. The server then marks the request as completed and returns to the listener, waiting for more requests.

Since the "worker" goroutine is independent of the handler, it continues to run even after the HTTP response has been sent. The operating system's scheduler allows it to share the CPU with other goroutines, and eventually, it will complete its sleep and print the completion message.

Exceptional Cases

There are only a few exceptional cases where a goroutine may not complete:

• Running out of memory: If the program runs out of memory, the entire system will crash, including all running goroutines.
• Unstable states: In rare circumstances, a goroutine may enter an unstable state due to various factors, such as deadlocks or panics. In such cases, the goroutine may not complete normally.

However, in stable and well-written programs like the one provided in your example, goroutines are expected to complete their tasks successfully.

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