How Does the Net Package Influence Deadlock Detection in Go Programs?

Interplay of Net Package Import and Deadlock Detection

In a Go program, if a channel operation blocks while the program is running, the program will eventually receive a "deadlock" error. However, the behavior changes when the net package is imported.

The code snippet in question:

<code class="go">package main

import (
    "fmt"
    "net/http"
)

func main() {
    var ch = make(chan int)
    ch <- 1
}</code>

If the net/http package is not imported, the program exits with a "deadlock" error. This is because the channel operation (sending to an unbuffered channel) blocks forever, and no other goroutine is running to perform asynchronous operations that would allow the deadlock detector to identify the issue.

However, when the net/http package is imported, the program does not deadlock. This is because importing the net package starts background polling Goroutines that effectively disable the deadlock detector.

The net package includes functionality for managing network connections, and it uses Goroutines to handle connections asynchronously. These background polling Goroutines keep running even if no HTTP connection is currently being established or processed, which makes the program appear non-blocking to the deadlock detector. As a result, the program does not exit with a "deadlock" error, despite the blocked channel operation.

This behavior has been discussed in the GitHub issue https://github.com/golang/go/issues/12734.

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