Channels: Buffered, Unbuffered & Closing Rules

Channels carry values and synchronization between goroutines.

Choosing buffered versus unbuffered capacity and following close ownership rules prevents deadlocks and panics in production pipelines.

Summary

An unbuffered channel synchronizes partners: the sender blocks until the receiver is ready.

A buffered channel stores up to cap values without a waiting receiver.

Closing a channel broadcasts "no more sends" to receivers; only senders should close.

range over a channel drains until close; the two-value receive v, ok := <-ch detects close explicitly.

Recipe

Quick-reference recipe card - copy-paste ready.

package main
 
import "fmt"
 
func main() {
    ch := make(chan int, 2) // buffered
    ch <- 1
    ch <- 2
    close(ch)
 
    for v := range ch {
        fmt.Println(v)
    }
 
    v, ok := <-ch
    fmt.Println(v, ok) // 0 false after drained close
}

When to reach for this:

• Unbuffered: handoff, ack, strict backpressure between stages.
• Buffered: smooth bursts when producer and consumer run at different speeds.
• Close: producer finished; consumers should exit range loops.
• Never close from the receiver side in shared pipelines.

Working Example

package main
 
import (
    "fmt"
    "sync"
)
 
func producer(out chan<- int, wg *sync.WaitGroup) {
    defer wg.Done()
    for i := 1; i <= 5; i++ {
        out <- i
    }
    close(out) // sender closes
}
 
func consumer(in <-chan int, wg *sync.WaitGroup) {
    defer wg.Done()
    for v := range in {
        fmt.Println("got", v)
    }
}
 
func main() {
    ch := make(chan int) // unbuffered - sync handoff
    var wg sync.WaitGroup
    wg.Add(2)
    go producer(ch, &wg)
    go consumer(ch, &wg)
    wg.Wait()
}

What this demonstrates:

• Directional types chan<- and <-chan document send-only/receive-only usage.
• Sender closes after last send so range in consumer terminates.
• Unbuffered channel couples producer and consumer timing.
• WaitGroup waits for both sides to finish.

Deep Dive

How It Works

• Channel send copies the value into the channel buffer or hands off directly (unbuffered).
• Receive copies out and frees a buffer slot or unblocks a sender.
• close(ch) sets closed flag; future receives get zero value with ok == false.
• Send on closed channel panics; receive on closed channel is safe (returns zero).
• len(ch) and cap(ch) report queued elements and capacity.

Buffered vs Unbuffered

Close Rules

Go Notes

// Fan-in: one goroutine closes after all senders done
func fanIn(inputs ...<-chan int) <-chan int {
    out := make(chan int)
    var wg sync.WaitGroup
    wg.Add(len(inputs))
    for _, in := range inputs {
        go func(c <-chan int) {
            defer wg.Done()
            for v := range c {
                out <- v
            }
        }(in)
    }
    go func() {
        wg.Wait()
        close(out)
    }()
    return out
}

Gotchas

• Send on closed channel - Panic. Fix: only sender closes; use sync.Once to guard close.
• Leak: receiver gone, sender blocks - Unbuffered send waits forever. Fix: context cancel, timeout select, or buffer.
• Range without close - Consumer blocks forever. Fix: sender must close or cancel upstream.
• Closing consumer-facing channel while sending - Race with in-flight sends. Fix: close only after all sends complete (often WaitGroup then close).
• Huge buffer masking overload - Memory grows, latency hides. Fix: size to SLA; shed load when full.

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Alternatives

FAQs

Related

• Concurrency Basics - first channel examples
• select Statement & Default Cases - multiplex receives
• Concurrency in Go: Goroutines and Channels First - CSP overview
• sync.Mutex, RWMutex & WaitGroup - shared state alternative
• Concurrency Fundamentals Best Practices - channel habits

Stack versions: This page was written for Go 1.26.x (Green Tea GC default, go fix modernizers - verify patch at build), chi (latest - verify at build), gin (latest - verify at build), echo (latest - verify at build), google.golang.org/grpc (latest - verify at build), sigs.k8s.io/controller-runtime (latest - verify at build), kubebuilder (latest - verify at build), tinygo (latest - verify board targets at build), wazero (latest - verify at build), and golangci-lint (latest - verify linter set at build).