How to debug deadlocks
yourbasic.org/golang
A deadlock happens when a group of goroutines are waiting for each other and none of them is able to proceed.
Take a look at this simple example.
func main() {
ch := make(chan int)
ch <- 1
fmt.Println(<-ch)
}
The program will get stuck on the channel send operation waiting forever for someone to read the value. Go is able to detect situations like this at runtime. Here is the output from our program:
fatal error: all goroutines are asleep - deadlock!
goroutine 1 [chan send]:
main.main()
.../deadlock.go:7 +0x6c
Debugging tips
A goroutine can get stuck
- either because it’s waiting for a channel or
- because it is waiting for one of the locks in the sync package.
Common reasons are that
- no other goroutine has access to the channel or the lock,
- a group of goroutines are waiting for each other and none of them is able to proceed.
Currently Go only detects when the program as a whole freezes, not when a subset of goroutines get stuck.
With channels it’s often easy to figure out what caused a deadlock. Programs that make heavy use of mutexes can, on the other hand, be notoriously difficult to debug.
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