All Goroutines Are Asleep — Deadlock

Why This Happens

Go detects a deadlock when all goroutines are blocked and none can proceed. This typically happens when you read from a channel that nothing will ever write to, lock a mutex that is already held by the same goroutine, or have circular dependencies between goroutines waiting on each other.

The Problem

func main() {
    ch := make(chan int)
    ch <- 42 // blocks forever, no receiver
    fmt.Println(<-ch)
}

The Fix

func main() {
    ch := make(chan int)
    go func() {
        ch <- 42
    }()
    fmt.Println(<-ch)
}

Step-by-Step Fix

1. 1

   Identify the blocked goroutines

   Read the panic output which shows the stack trace of each blocked goroutine and what it is waiting on.

2. 2

   Find the circular dependency

   Map out which goroutine is waiting for which channel or lock, and find the cycle.

3. 3

   Break the cycle

   Use a separate goroutine for the send or receive, use buffered channels, or restructure the synchronization logic.