How does importing the net/http package in Go affect deadlock error detection?

Avoiding Deadlock Errors with Go HTTP Imports

In Go, using the net/http package for HTTP communication introduces a subtle behavior that can affect the detection of deadlocks.

Consider the following code:

<code class="go">package main

import (
    "fmt"
    "net/http"
)

func Extract(url string) ([]string, error) {
    http.Get(url)

    var links []string
    return links, nil
}

func crawl(url string) []string {
    list, _ := Extract(url)
    return list
}

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

Without the net/http import, running this code would result in a "deadlock" error. This is because the Extract function is blocked on an HTTP request without a corresponding call to ServeHTTP or Close.

However, if the net/http package is imported, even without calling the Extract function, the "deadlock" error disappears. This is because importing the net package starts background polling Goroutines that automatically communicate with the HTTP server.

This behavior is documented in the Go blog post "Goroutine Pooling in NetHttp":

"The net package begins a simple background goroutine that periodically tests reachability to the HTTP server. The simple test goroutine exits if HTTP server isn't reachable and then re-starts when server becomes reachable. This makes sure that goroutines that have net.Dial in their call stack are not erroneously reported as being blocked."

Importing the net package effectively disables the deadlock detector for any code that uses net.Dial, which includes HTTP communication.

For applications that require stricter deadlock detection, it is recommended to avoid importing the net package until it is necessary to establish communication with an HTTP server.

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