Going Async in Go

Johannes Pelto-Piri & Oskar Wickström

What is Go?

Go is an open source programming environment that makes it easy to build simple, reliable, and efficient software.

Overview

• Open source, backed by Google
• Compiled
• Statically typed
• Garbage collected
• Concurrent

Hello World in Go

Packages

• Functions, types, variables and constants in packages are visible from other packages if the first character is uppercase. E.g. MyFunction is visible, myState is not.
• A main function must reside in the main package.
• A package name is the last name in the import path. When importing "net/http" you are importing the http package.
• The package name does not need to be unique in the linked executable, only the full import path.

Variables

References and Values

• When passing an object as a value, the struct is copied to the stack.
• When passing an object as a reference, you pass a pointer to the object.
• References can be dereferenced (*reference) and values can be referenced (&value).

Slices

• Slices wraps the more low level arrays in Go, and are the most commonly used sequence type.
• They are variable length and can have a fixed capacity.

Slices and Slicing

Maps

• Go provides a built-in map type that implements a hash table.
• Keys must be Comparable while values can be anything.
• Maps are not safe when used concurrently.
• No iteration order.

Working with Maps

Multiple Return Values

Defer

• defer schedules a function to be called before returning from the function calling defer.
• The arguments of the deferred function are evaluated when the function is called, not at the call to defer.
• The order of deferred function execution is FILO.

Closing a file with defer

Interfaces

• They are satisfied implicitly.
• Statically checked to avoid runtime errors.
• In short, statically checked duck typing.

Interfaces Example

Concurrency in Go

• Goroutines are small lightweight processes that are managed by Go's runtime.
• Channels are first class citizen that connects Goroutines.
• A channel may be buffered or unbuffered, an unbuffered channel will always block until there is a receiver.
• Channels are by default unbuffered.

Ping Pong

Goroutines are Cheap

• ~4KB initial memory overhead.
• They are multiplexed across OS threads.
• Goroutines do not block on IO.

Non-blocking IO in Goroutines

Lots of routines and channels

Buffered Channels

Select over Channels

Timing Out

Channel Directions

• Channels can be typed to have a direction.
• chan<- string can only be sent to.
• <-chan string can only be received from.

Closing Channels

Iterating Channel Messages

Timers & Tickers using Channels

Other Channel Operations

• len(c) returns the number of elements in a channel. In a non-buffered channel this is always 0.
• cap(c) returns the element capacity in a channel. In a non-buffered channel this is always 0.

GOMAXPROCS

• Sets the maximum number of OS threads used for Goroutines multiplexing.
• Can be set programatically with runtime.GOMAXPROCS(0).
• Will be removed when the Go scheduler improves.