Flowing with Context

In this session, we will observe how a flowing context can help you optimize the resource usage of your server and enables context-based programming.

We will dive deeper into how context package works and why it is present in the Go as a native package at first place and how things were before this package. We will see different use cases of Context package and the do’s and don’ts being followed among the Gophers.

Transcript

1. Flowing with Context @duayashish
2. Disclaimer: Views are my personal. Not expressed to hurt any developers' feeling.
3. What is Context?
6. Importance of Context From real life's perspective
7. Importance of Context Better decisions From real life's perspective
8. Importance of Context Better decisions No wastage of resources From real life's perspective
9. Importance of Context Better decisions No wastage of resources Shared entities not leaked From real life's perspective
10. Importance of Context From applications' perspective
11. Importance of Context Request scoped values From applications' perspective
12. Importance of Context Request scoped values Cancellation signals From applications' perspective
13. Importance of Context Request scoped values Cancellation signals Deadlines and Timeouts From applications' perspective
14. Context API in Go
15. Context API in Go A Context carries a deadline, cancellation signal, and request-scoped values across API boundaries.
16. Context API in Go A Context carries a deadline, cancellation signal, and request-scoped values across API boundaries. Its methods are safe for simultaneous use by multiple goroutines.
18. Derived Context The context package provides functions to derive new Context values from existing ones. These values form a tree: when a Context is canceled, all Contexts derived from it are also canceled.
19. 1. Background Background returns an empty Context. It is never canceled, has no deadline, and has no values. Background is typically used in main, init, and tests, and as the top-level Context for incoming requests. func Background() Context
20. 2. WithCancel WithCancel returns a copy of parent whose Done channel is closed as soon as parent.Done is closed or cancel is called. func WithCancel (parent Context) (ctx Context, cancel CancelFunc)
21. 3. WithTimeout WithTimeout returns a copy of parent whose Done channel is closed as soon as parent.Done is closed, cancel is called, or timeout elapses. func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)
23. Context.Value Important points to remember
24. Context.Value Context.Value is for informing not controlling Important points to remember
25. Context.Value Context.Value is for informing not controlling Context.Value should NEVER be used for values that are not created and destroyed during the lifetime of the request Important points to remember
26. Advantages
27. Advantages It separates the core computation parameters from the operational parameters.
28. Advantages It separates the core computation parameters from the operational parameters. It codifies common operational aspects and how to communicate them across boundaries.
29. Advantages It separates the core computation parameters from the operational parameters. It codifies common operational aspects and how to communicate them across boundaries. Optimize resource usage
30. Criticism
31. Criticism No acknowledgement of cancelation
32. Criticism No acknowledgement of cancelation More prone to errors since avoiding static type checks
33. Criticism No acknowledgement of cancelation More prone to errors since avoiding static type checks Unnecessarily bloats function signature
34. Okay, better practices!
35. Okay, better practices! Most functions that use a Context should accept it as their first parameter: func F(ctx context.Context, /* other arguments */) {}
36. Okay, better practices! Most functions that use a Context should accept it as their first parameter: func F(ctx context.Context, /* other arguments */) {} A function that is never request-specific may use context.Background() or context.TODO()
38. Contexts are immutable, so it's fine to pass the same ctx to multiple calls that share the same deadline, cancellation signal, credentials, parent trace, etc
39. Contexts are immutable, so it's fine to pass the same ctx to multiple calls that share the same deadline, cancellation signal, credentials, parent trace, etc Context should always be flowing
40. With Context, thank you! @duayashish