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Concurrency in Depth

Context Cancellation

Deadlines, cancellation trees, request-scoped values, and signal-aware shutdown.

7 min readGo for SREBuild

Context Basics

Context carries deadlines, cancellation signals, and request-scoped values across goroutine boundaries. It is the standard way to control goroutine lifetimes in Go.

Gocontext-creation.go

21 linesLn 1, Col 1Go

context.Background() is the root context. context.WithCancel creates a cancellable child. WithTimeout and WithDeadline add time-based cancellation. WithValue adds key-value pairs. Always defer cancel() to prevent resource leaks.

Cancellation Trees

Contexts form a tree. Canceling a parent cancels all its children. This is how request cancellation propagates through a call stack.

Gocancellation-propagation.go

38 linesLn 1, Col 1Go

Context cancellation propagates downward through the tree. Canceling a parent immediately cancels all children. Children can be canceled independently without affecting siblings or parents. This creates a clean shutdown hierarchy.

Deadlines and Timeouts

Deadlines and timeouts propagate through context chains. If a parent has a shorter deadline than a child, the parent's deadline wins.

Godeadline-propagation.go

35 linesLn 1, Col 1Go

The effective deadline is the earliest deadline in the chain. If a parent has a 10-second deadline and a child sets a 5-second deadline, the child expires after 5 seconds. If the child sets 15 seconds, the parent's 10-second deadline wins.

Request-Scoped Values

context.WithValue carries request-scoped data: request IDs, authentication tokens, and tracing spans. Use typed keys to avoid collisions.

Gocontext-values.go

30 linesLn 1, Col 1Go

Use unexported types as keys to prevent collisions with other packages. Values should be request-scoped — do not put database connections or configuration in context. Values are immutable — WithValue creates a new context.

Signal Integration

Signal context converts OS signals into context cancellation. This is the standard pattern for graceful shutdown.

Gosignal-aware-context.go

44 linesLn 1, Col 1Go

signal.NotifyContext creates a context that is canceled when the specified signals are received. This is the cleanest pattern — the entire application uses context cancellation for shutdown. No global variables or channels needed.

Anti-Patterns

Gocontext-anti-patterns.go

38 linesLn 1, Col 1Go

Do not store context in structs. Do not put non-request-scoped values in context. Always check context.Done() in loops. Pass context as the first parameter to functions. Use function parameters for dependencies, not context values.

Context is for cancellation, not dependency injection

Context carries deadlines, cancellation signals, and request-scoped values. It is not a general-purpose dependency injection container. Pass databases, loggers, and config as function parameters. Use context only for request-scoped data.

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.

Stage 3 · Build

Concurrency in Depth

Context Cancellation

Deadlines, cancellation trees, request-scoped values, and signal-aware shutdown.

7 min readGo for SREBuild

Context Basics

Context carries deadlines, cancellation signals, and request-scoped values across goroutine boundaries. It is the standard way to control goroutine lifetimes in Go.

Gocontext-creation.go

21 linesLn 1, Col 1Go

Cancellation Trees

Contexts form a tree. Canceling a parent cancels all its children. This is how request cancellation propagates through a call stack.

Gocancellation-propagation.go

38 linesLn 1, Col 1Go

Deadlines and Timeouts

Deadlines and timeouts propagate through context chains. If a parent has a shorter deadline than a child, the parent's deadline wins.

Godeadline-propagation.go

35 linesLn 1, Col 1Go

Request-Scoped Values

context.WithValue carries request-scoped data: request IDs, authentication tokens, and tracing spans. Use typed keys to avoid collisions.

Gocontext-values.go

30 linesLn 1, Col 1Go

Signal Integration

Signal context converts OS signals into context cancellation. This is the standard pattern for graceful shutdown.

Gosignal-aware-context.go

44 linesLn 1, Col 1Go

Anti-Patterns

Gocontext-anti-patterns.go

38 linesLn 1, Col 1Go

Context is for cancellation, not dependency injection

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.