How to Use sync.Cond in Go

Use sync.Cond to block goroutines until a specific condition is met by wrapping a sync.Mutex and signaling with Signal or Broadcast.

import "sync"

var (
    mu    sync.Mutex
    cond  = sync.NewCond(&mu)
    ready = false
)

// Waiter blocks until ready is true
func wait() {
    mu.Lock()
    for !ready {
        cond.Wait()
    }
    // Critical section
    mu.Unlock()
}

// Signaler sets ready and wakes one waiter
func signal() {
    mu.Lock()
    ready = true
    cond.Signal()
    mu.Unlock()
}

The Wait() method atomically unlocks the mutex and blocks until Signal() or Broadcast() is called. Always check the condition in a loop because spurious wakeups can occur.

sync.Cond is a tool that lets multiple parts of your program pause and wait for a specific event to happen. Think of it like a waiter at a restaurant who stops working until the chef signals that a table is ready. You use it when you need one part of your code to pause efficiently until another part finishes a task or changes a state.