Why Does an Infinite-Loop Goroutine Block a Go HTTP Server Despite Sufficient Resources?

Infinite-Loop Goroutine Blocks Go HTTP Server

The Go runtime, responsible for managing concurrent execution, prides itself on non-blocking operations. However, a scenario involving an infinite-loop goroutine initiated from within an HTTP server raises a concern. Despite having enough threads and goroutines (according to runtime.GOMAXPROCS), this infinite loop appears to block the server's handling of other requests.

To illustrate the issue, you've provided sample code featuring a server with an infinite-loop goroutine (disabled by default) and a client sending concurrent HTTP requests. With the goroutine disabled, the client displays the expected set of asterisks. However, enabling it leads to a blockade in the client's output after a handful of requests.

The mystery persists even after experimenting with runtime.LockOSThread within the goroutine, as it fails to resolve the blockage. According to Go's documentation, runtime.LockOSThread should execute the infinite loop in a separate thread, leaving other goroutines unaffected.

This puzzling behavior could be attributed to the Go runtime scheduler. Although preemptive to an extent, it's not entirely so. Go 1.2 introduced improvements by forcing occasional scheduler invocations during function calls. However, the infinite loops in this example lack function calls, bypassing this solution.

Consider adding meaningful work to your infinite loop handlers. Alternatively, a deliberate call to runtime.Gosched could alleviate the blocking issue.

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