Go: What is the difference between goroutine and thread?

Goroutine — lightweight concurrency primitive managed by Go runtime. Thread — OS-level execution unit with dedicated kernel resources.

Stack allocation:

• Goroutines start with 2KB stack, grow dynamically (up to 1GB).
• Threads start with 1-8MB stack, cannot resize.
• This enables millions of concurrent goroutines.

Scheduling model:

• Goroutines: cooperative scheduling by Go runtime (M:N threading).
• Threads: preemptive scheduling by OS kernel (1:1 threading).
• Go scheduler uses work stealing across P processors.

Performance characteristics:

• Goroutine creation: ~2µs, ~2KB memory.
• Thread creation: ~10-100µs, ~1-8MB memory.
• Context switch: goroutine ~100ns vs thread ~1-10µs.

1// Goroutine-based concurrent server
2func handleConnections(ln net.Listener) {
3    for {
4        conn, err := ln.Accept()
5        if err != nil {
6            log.Println("accept error:", err)
7            continue
8        }
9        go handleConnection(conn) // one goroutine per connection
10    }
11}

When to use goroutines:

• High-concurrency servers (thousands of connections).
• Background tasks and workers.
• Fan-out/fan-in patterns.
• I/O-bound operations.

When to use threads:

• Cgo interop.
• Thread-local storage.
• Long-running CPU-bound tasks.

Common mistakes:

• Not synchronizing goroutine completion.
• Closure variable capture in loops.
• Assuming goroutines are always parallel.
• Creating too many goroutines without backpressure.
• Using runtime.LockOSThread() unnecessarily.