Is there any other way that goroutines can communicate with eachother, Other than channels?

I had been interview today and one of the interesting that i come across from the interviewer is we know that Channels are the medium through which goroutines can communicate with each other.

But, What if they is no channels..! or do not want to use channels, Is there any other alternative way that we can send and read messages to goroutines in golang?

If yes, How is it so?

Channel is not the first nor the only communication tool between concurrent or parallel entities. There are numerous others.

As a sarcastic example, one goroutine may upload a file holding the message to Amazon S3, and the other goroutine can fetch that file. This is a communication.

A more efficient one would be to create and write the message to a local file which the other goroutine can read.

Another could be opening a server socket by one goroutine, and connecting to that socket from the other goroutine. And you have a full duplex "channel".

To stay on the "Earth", much simpler and more efficient solutions would be to send messages via a shared variable, but access to it must be synchronized of course via synchronization primitives such as those in the sync and sync/atomic packages.

A slice (of messages) may be shared by the 2 goroutines, and when the first goroutine wants to send a message to the other, it may acquire a write lock (sync.RWMutex), append the message to the slice then release the lock. The second goroutine may use a read lock to check if the slice has messages (length > 0), then use a write lock to take a message from the slice (and delete it).