Can Buffered Channels Be Used for Implementing Buffered Locking in Go?

Buffered Locking in Go

In Go, buffered channels allow communication without blocking until the buffer is full. This raises the question: is there a general pattern for buffered locking, where a resource is locked for a limited number of clients?

Answer: Semaphores

The primitive for locking a resource for a limited number of clients is a semaphore. A semaphore is easily implemented using a buffered channel.

Consider the following example:

var semaphore = make(chan struct{}, 4) // allow four concurrent users

func f() {
    // Grab the lock. Blocks as long as 4 other invocations of f are still running.
    semaphore <- struct{}{}

    // Release the lock once we're done.
    defer func() { <-semaphore }()

    // Do work...
}

In this example, the buffered channel with four elements (make(chan struct{}, 4)) acts as a semaphore. The f function grabs the lock by sending a value to the channel. If the channel is full, the function will block until a value is received. Once the lock is acquired, the defer statement ensures that the lock is released when the function returns.

By using semaphores implemented with buffered channels, you can create buffered locking patterns that restrict access to a resource to a limited number of concurrent users.

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