// cancelation signals, and other request-scoped values across API boundaries
// and between processes.
//
-// Incoming requests to a server should create a Context, and outgoing calls to
-// servers should accept a Context. The chain of function calls between them
-// must propagate the Context, optionally replacing it with a derived Context
-// created using WithCancel, WithDeadline, WithTimeout, or WithValue. These
-// Context values form a tree: when a Context is canceled, all Contexts derived
-// from it are also canceled.
+// Incoming requests to a server should create a Context, and outgoing
+// calls to servers should accept a Context. The chain of function
+// calls between them must propagate the Context, optionally replacing
+// it with a derived Context created using WithCancel, WithDeadline,
+// WithTimeout, or WithValue. When a Context is canceled, all
+// Contexts derived from it are also canceled.
//
-// The WithCancel, WithDeadline, and WithTimeout functions return a derived
-// Context and a CancelFunc. Calling the CancelFunc cancels the new Context and
-// any Contexts derived from it, removes the Context from the parent's tree, and
-// stops any associated timers. Failing to call the CancelFunc leaks the
-// associated resources until the parent Context is canceled or the timer fires.
+// The WithCancel, WithDeadline, and WithTimeout functions take a
+// Context (the parent) and return a derived Context (the child) and a
+// CancelFunc. Calling the CancelFunc cancels the child and its
+// children, removes the parent's reference to the child, and stops
+// any associated timers. Failing to call the CancelFunc leaks the
+// child and its children until the parent is canceled or the timer
+// fires. The go vet tool checks that CancelFuncs are used on all
+// control-flow paths.
//
// Programs that use Contexts should follow these rules to keep interfaces
// consistent across packages and enable static analysis tools to check context
// propagation:
//
// Do not store Contexts inside a struct type; instead, pass a Context
-// explicitly to each function that needs it. The Context should be the first
+// explicitly to each function that needs it. The Context should be the first
// parameter, typically named ctx:
//
// func DoSomething(ctx context.Context, arg Arg) error {
// // ... use ctx ...
// }
//
-// Do not pass a nil Context, even if a function permits it. Pass context.TODO
+// Do not pass a nil Context, even if a function permits it. Pass context.TODO
// if you are unsure about which Context to use.
//
// Use context Values only for request-scoped data that transits processes and
// Context's methods may be called by multiple goroutines simultaneously.
type Context interface {
// Deadline returns the time when work done on behalf of this context
- // should be canceled. Deadline returns ok==false when no deadline is
- // set. Successive calls to Deadline return the same results.
+ // should be canceled. Deadline returns ok==false when no deadline is
+ // set. Successive calls to Deadline return the same results.
Deadline() (deadline time.Time, ok bool)
// Done returns a channel that's closed when work done on behalf of this
- // context should be canceled. Done may return nil if this context can
- // never be canceled. Successive calls to Done return the same value.
+ // context should be canceled. Done may return nil if this context can
+ // never be canceled. Successive calls to Done return the same value.
//
// WithCancel arranges for Done to be closed when cancel is called;
// WithDeadline arranges for Done to be closed when the deadline
// a Done channel for cancelation.
Done() <-chan struct{}
- // Err returns a non-nil error value after Done is closed. Err returns
+ // Err returns a non-nil error value after Done is closed. Err returns
// Canceled if the context was canceled or DeadlineExceeded if the
- // context's deadline passed. No other values for Err are defined.
+ // context's deadline passed. No other values for Err are defined.
// After Done is closed, successive calls to Err return the same value.
Err() error
// Value returns the value associated with this context for key, or nil
- // if no value is associated with key. Successive calls to Value with
+ // if no value is associated with key. Successive calls to Value with
// the same key returns the same result.
//
// Use context values only for request-scoped data that transits
// processes and API boundaries, not for passing optional parameters to
// functions.
//
- // A key identifies a specific value in a Context. Functions that wish
+ // A key identifies a specific value in a Context. Functions that wish
// to store values in Context typically allocate a key in a global
// variable then use that key as the argument to context.WithValue and
- // Context.Value. A key can be any type that supports equality;
+ // Context.Value. A key can be any type that supports equality;
// packages should define keys as an unexported type to avoid
// collisions.
//
// // This prevents collisions with keys defined in other packages.
// type key int
//
- // // userKey is the key for user.User values in Contexts. It is
+ // // userKey is the key for user.User values in Contexts. It is
// // unexported; clients use user.NewContext and user.FromContext
// // instead of using this key directly.
// var userKey key = 0
func (deadlineExceededError) Timeout() bool { return true }
-// An emptyCtx is never canceled, has no values, and has no deadline. It is not
+// An emptyCtx is never canceled, has no values, and has no deadline. It is not
// struct{}, since vars of this type must have distinct addresses.
type emptyCtx int
)
// 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,
+// 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.
func Background() Context {
return background
}
-// TODO returns a non-nil, empty Context. Code should use context.TODO when
+// 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). TODO is recognized by static analysis tools that determine
+// parameter). TODO is recognized by static analysis tools that determine
// whether Contexts are propagated correctly in a program.
func TODO() Context {
return todo
}
// parentCancelCtx follows a chain of parent references until it finds a
-// *cancelCtx. This function understands how each of the concrete types in this
+// *cancelCtx. This function understands how each of the concrete types in this
// package represents its parent.
func parentCancelCtx(parent Context) (*cancelCtx, bool) {
for {
p.mu.Unlock()
}
-// A canceler is a context type that can be canceled directly. The
+// A canceler is a context type that can be canceled directly. The
// implementations are *cancelCtx and *timerCtx.
type canceler interface {
cancel(removeFromParent bool, err error)
Done() <-chan struct{}
}
-// A cancelCtx can be canceled. When canceled, it also cancels any children
+// A cancelCtx can be canceled. When canceled, it also cancels any children
// that implement canceler.
type cancelCtx struct {
Context
}
// WithDeadline returns a copy of the parent context with 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
+// 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's 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.
return c, func() { c.cancel(true, Canceled) }
}
-// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to
-// implement Done and Err. It implements cancel by stopping its timer then
+// A timerCtx carries a timer and a deadline. It embeds a cancelCtx to
+// implement Done and Err. It implements cancel by stopping its timer then
// delegating to cancelCtx.cancel.
type timerCtx struct {
cancelCtx
return &valueCtx{parent, key, val}
}
-// A valueCtx carries a key-value pair. It implements Value for that key and
+// A valueCtx carries a key-value pair. It implements Value for that key and
// delegates all other calls to the embedded Context.
type valueCtx struct {
Context