Channel in Go provides a connection between two goroutines, allowing them to communicate and synchronize the exchange of any resource that is passed through it.
It is the channel’s ability to control the goroutines interaction that creates the synchronization mechanism.
When a channel is created with no capacity, it is called an unbuffered channel. In turn, a channel created with capacity is called a buffered channel.
chan T // can be used to send and receive values of type T
chan <- float64 // can only be used to send float64s
<-chan int // can only be used to receive ints
Unbuffered channels have no capacity and therefore require both goroutines to be ready to make any exchange.
When a goroutine attempts to send a resource to an unbuffered channel and there is no goroutine waiting to receive the resource, the channel will lock the sending goroutine and make it wait.
When a goroutine attempts to receive from an unbuffered channel, and there is no goroutine waiting to send a resource, the channel will lock the receiving goroutine and make it wait. Synchronization is inherent in the interaction between the send and the receive. One can not happen without the other.
Example
package main
import "fmt"
func main() {
c := make(chan int)
// c <- 40 // This code alone will not work as channel blocks without synchronization
go func() { // This is sender, sync is done using goroutine
c <- 40
}()
fmt.Print(<-c) // Receiver - This is main go routine
}