Detecting a Full Buffered Channel

In Go, buffered channels have a maximum capacity limit. When a buffered channel reaches its capacity, sending additional items to it will typically result in the operation blocking. However, there are situations where you may prefer to drop items instead of blocking.

Using a Select Statement with Default

One way to determine whether a buffered channel is full is to use a select statement with a default clause. Here's an example:

package main

import "fmt"

func main() {
    ch := make(chan int, 1)

    // Fill it up
    ch 
In this example, the select statement has two cases:

• The first case attempts to send the value 2 to the channel. If the channel is not full, the operation will succeed.
• The default case is executed if none of the cases can be immediately executed. Since the channel is already full, the default case will be triggered, and the value 2 will be discarded.

Output:

Channel full. Discarding value

Checking Channel Size

Another method for detecting a full channel is to check its size using len(ch) and compare it to its capacity using cap(ch).

if len(ch) == cap(ch) {
    // Channel was full, but might not be by now
} else {
    // Channel wasn't full, but might be by now
}

Note that this approach does not guarantee the result will be valid by the time the if block is entered due to the possibility of channel activity between the size check and the if statement.