Why Does an Empty `select {}` Statement Block in Go?

Understanding the Purpose of an Empty select Statement

In the given code snippet, we can observe the use of an empty select statement (select {}). To comprehend the behavior of such a statement, let's delve into its mechanics in Go.

An empty select statement serves as a blocking mechanism, similar to an empty for statement. However, there are subtle differences between the two.

Blocking Nature of select {}

When a select statement is empty, it effectively means that there are no channels or case statements to select from. As a result, the select statement will block indefinitely, waiting for a channel to become ready for reading or writing.

Comparison to for {}

Although both empty select and for statements block execution, they handle CPU resources differently. On most Go architectures, an empty select statement yields the CPU, allowing other threads or processes to execute. In contrast, an empty for loop consumes CPU resources by repeatedly checking the loop condition, resulting in a constant 100% CPU utilization.

In the provided code example, the empty select statement is used to block execution until a signal is received from elsewhere in the program. When *serve is a non-empty string, the statement is executed, and the server remains operational until the select statement is unblocked.

By understanding the blocking behavior of an empty select statement, developers can effectively utilize this mechanism for blocking and synchronization purposes in their Go programs.

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