Context (Deprecated)

Package context has been superseded by the standard library context package.

Deprecated: Use the standard library context package instead.

Import

import "golang.org/x/net/context"

Variables

var Canceled = context.Canceled
var DeadlineExceeded = context.DeadlineExceeded

• Canceled: The error returned by Context.Err when the context is canceled for some reason other than its deadline passing
• DeadlineExceeded: The error returned by Context.Err when the context is canceled due to its deadline passing

Types

// Context carries a deadline, a cancellation signal, and other values across API boundaries
type Context = context.Context

// CancelFunc tells an operation to abandon its work
type CancelFunc = context.CancelFunc

Context's methods may be called by multiple goroutines simultaneously. A CancelFunc does not wait for the work to stop. A CancelFunc may be called by multiple goroutines simultaneously. After the first call, subsequent calls to a CancelFunc do nothing.

Functions

// Background returns a non-nil, empty Context
func Background() Context

// TODO returns a non-nil, empty Context
func TODO() Context

// WithCancel returns a derived context with a new Done channel
func WithCancel(parent Context) (ctx Context, cancel CancelFunc)

// WithDeadline returns a derived context with a deadline
func WithDeadline(parent Context, d time.Time) (Context, CancelFunc)

// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout))
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc)

// WithValue returns a derived context with an associated key-value pair
func WithValue(parent Context, key, val interface{}) Context

Background

Background returns a non-nil, empty Context. It is never canceled, has no values, and has no deadline. It is typically used by the main function, initialization, and tests, and as the top-level Context for incoming requests.

TODO

TODO returns a non-nil, empty Context. Code should use context.TODO when it's unclear which Context to use or it is not yet available (because the surrounding function has not yet been extended to accept a Context parameter).

WithCancel

WithCancel returns a derived context that points to the parent context but has a new Done channel. The returned context's Done channel is closed when the returned cancel function is called or when the parent context's Done channel is closed, whichever happens first.

Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete.

WithDeadline

WithDeadline returns a derived context that points to the parent context but has the deadline adjusted to be no later than d. If the parent's deadline is already earlier than d, WithDeadline(parent, d) is semantically equivalent to parent. The returned Context.Done channel is closed when the deadline expires, when the returned cancel function is called, or when the parent context's Done channel is closed, whichever happens first.

Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete.

WithTimeout

WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).

Canceling this context releases resources associated with it, so code should call cancel as soon as the operations running in this Context complete.

Example:

func slowOperationWithTimeout(ctx context.Context) (Result, error) {
    ctx, cancel := context.WithTimeout(ctx, 100*time.Millisecond)
    defer cancel() // releases resources if slowOperation completes before timeout elapses
    return slowOperation(ctx)
}

WithValue

WithValue returns a derived context that points to the parent Context. In the derived context, the value associated with key is val.

Use context Values only for request-scoped data that transits processes and APIs, not for passing optional parameters to functions.

The provided key must be comparable and should not be of type string or any other built-in type to avoid collisions between packages using context. Users of WithValue should define their own types for keys. To avoid allocating when assigning to an interface{}, context keys often have concrete type struct{}. Alternatively, exported context key variables' static type should be a pointer or interface.