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thread-safetygolockless

Is Go's buffered channel lockless?

Go's buffered channel is essentially a thread-safe FIFO queue. (See Is it possible to use Go's buffered channel as a thread-safe queue?)

I am wondering how it's implemented. Is it lock-free like described in Is there such a thing as a lockless queue for multiple read or write threads??

greping in Go's src directory (grep -r Lock .|grep chan) gives following output:

./pkg/runtime/chan.c:   Lock;
./pkg/runtime/chan_test.go: m.Lock()
./pkg/runtime/chan_test.go: m.Lock() // wait
./pkg/sync/cond.go: L Locker // held while observing or changing the condition

Doesn't to be locking on my machine (MacOS, intel x86_64) though. Is there any official resource to validate this?

Solution

  • If you read the runtime·chansend function in chan.c, you will see that runtime·lock is called before the check to see if the channel is buffered if(c->dataqsiz > 0).

    In other words, buffered channels (and all channels in general) use locks.

    The reason your search did not find it was you were looking for "Lock" with a capital L. The lock function used for channels is a non-exported C function in the runtime.