Understanding Go’s Context Type
Understand the context package in Go and its usage.
Go provides a package called context that is useful for two purposes, as outlined here:
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Canceling a chain of function calls after some event (such as a timeout)
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Passing information through a chain of function calls (such as user information)
A Context object is usually created in either main() or at the point of ingestion of some request (such as an RPC or HyperText Transfer Protocol (HTTP) request).
A basic Context object is created from our background Context object, as follows:
import "context"func main() {ctx := context.Background()}
The context package and the Context type is an advanced subject, but we introduce it here as it is used throughout the Go ecosystem.
Using a Context to signal a timeout
Context is often used to communicate a timer state or to terminate a wait condition, for example, when our program is waiting for a network response.
Let's say we want to call a function to get some data, but we don't want to wait longer than 5 seconds for the call to complete. We can signal this via a Context, as follows:
ctx, cancel := context.WithTimeout(context.Background(), 5 * time.Second)data, err := GatherData(ctx, args)cancel()if err != nil {return err}
context.WithTimeout() creates a new Context that will automatically be canceled after 5 seconds and a function that will cancel the Context (context.CancelFunc) when called.
Every Context is said to be derived from another Context. Here, we derive our ctx object from context.Background(). The context.Background() is our parent Context. New context objects can be derived from ...