Context

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What a context carries

AI-generated

context.Context carries a cancellation signal, deadline, and request-scoped values across API boundaries. It is safe for use by multiple goroutines.

Use context for work lifetime, not as an optional-parameter bag. Pass it as the first parameter, usually named ctx, and do not store it in a struct unless an API specifically requires that pattern.

Hierarchy

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Derived contexts form a tree. Canceling a parent cancels every descendant, while a child cannot cancel its parent.

Go context cancellation treeParent cancellation propagates to all descendants, while child cancellation stops only that subtree.Go context cancellation tree Canceling a parent context propagates cancellation to every descendant, while canceling a child does not affect its parent or siblings. {"provenance": "AI-generated", "sourceAssets": []} Cancellation flows from parent to descendants request context database timeout2 seconds downstream timeout500 milliseconds query goroutine audit goroutine HTTP call goroutine derive derive Canceling the parent reaches every descendant; child cancellation stops only that subtree. 

ctx, cancel := context.WithTimeout(parent, 2*time.Second)
defer cancel()

select {
case result := <-work(ctx):
    return result, nil
case <-ctx.Done():
    return Result{}, ctx.Err()
}

Call the returned cancel function even when the timeout does not fire; it releases the associated timer and references promptly.

Context - Applied

AI-generated

func findUser(ctx context.Context, db *sql.DB, id int64) (User, error) {
    var user User
    err := db.QueryRowContext(
        ctx,
        `SELECT id, name FROM users WHERE id = ?`,
        id,
    ).Scan(&user.ID, &user.Name)
    return user, err
}

Use WithValue only for request-scoped metadata that crosses API boundaries, such as a request ID. Use an unexported key type to avoid collisions. Required business inputs should remain ordinary typed parameters.

Further reading: Go context package and Go concurrency patterns: context.

Concurrency Database Programming