Can you explain what a conditional variable sync.Cond in Go language is and what it is used for?

In Go language, sync.Cond is a structure that implements a condition variable used for goroutine synchronization. It allows one or more goroutines to wait for a certain condition to become true and to notify other goroutines when this condition changes.

Main methods of sync.Cond:

• Wait() — blocks the current goroutine until another goroutine calls Signal() or Broadcast().
• Signal() — wakes up one goroutine waiting on the condition variable.
• Broadcast() — wakes up all goroutines waiting on the condition variable.

Example usage:

var mu sync.Mutex
cond := sync.NewCond(&mu)

// Goroutine waiting for a signal
go func() {
    mu.Lock()
    cond.Wait() // wait for the signal
    // perform actions after waking up
    mu.Unlock()
}()

// Goroutine sending a signal
mu.Lock()
cond.Signal() // wake up one goroutine
mu.Unlock()

Thus, sync.Cond helps coordinate the work of multiple goroutines waiting for certain conditions to be met.