The select Keyword

Importance of the select keyword

The select keyword is really important because it allows us to listen to multiple channels at the same time. A select block can have multiple cases and an optional default case, which mimics the switch statement. It is good for select blocks to have a timeout option just in case. Last, a select without any cases (select{}) waits forever.

In practice, this means that select allows a goroutine to wait on multiple communication operations. So, select gives us the power to listen to multiple channels using a single select block. As a consequence, we can have nonblocking operations on channels, provided that we have implemented our select blocks appropriately.

A select statement is not evaluated sequentially, as all of its channels are examined simultaneously. If none of the channels in a select statement are ready, the select statement blocks (waits) until one of the channels is ready. If multiple channels of a select statement are ready, then the Go runtime makes a random selection from the set of these ready channels.

Coding example

The code in select.go presents a simple use of select running in a goroutine that has three cases. But first, let’s see how the goroutine that contains select runs: