前言 - context 源碼 可以先瞭解官方 context.go 輪廓. 這裡捎帶保存一份當前 context 版本備份. golang 標準庫 1.7 版本引入 context 包, 用於 golang 函數鏈安全的管理和控制. 說真 golang context 實現非常漂亮, 代碼中說明也 ...
前言 - context 源碼
可以先瞭解官方 context.go 輪廓. 這裡捎帶保存一份當前 context 版本備份.
// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package context defines the Context type, which carries deadlines,
// cancellation 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. When a Context is canceled, all
// Contexts derived from it are also canceled.
//
// 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
// 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
// if you are unsure about which Context to use.
//
// Use context Values only for request-scoped data that transits processes and
// APIs, not for passing optional parameters to functions.
//
// The same Context may be passed to functions running in different goroutines;
// Contexts are safe for simultaneous use by multiple goroutines.
//
// See https://blog.golang.org/context for example code for a server that uses
// Contexts.
package context
import (
"errors"
"internal/reflectlite"
"sync"
"time"
)
// A Context carries a deadline, a cancellation signal, and other values across
// API boundaries.
//
// 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.
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.
//
// WithCancel arranges for Done to be closed when cancel is called;
// WithDeadline arranges for Done to be closed when the deadline
// expires; WithTimeout arranges for Done to be closed when the timeout
// elapses.
//
// Done is provided for use in select statements:
//
// // Stream generates values with DoSomething and sends them to out
// // until DoSomething returns an error or ctx.Done is closed.
// func Stream(ctx context.Context, out chan<- Value) error {
// for {
// v, err := DoSomething(ctx)
// if err != nil {
// return err
// }
// select {
// case <-ctx.Done():
// return ctx.Err()
// case out <- v:
// }
// }
// }
//
// See https://blog.golang.org/pipelines for more examples of how to use
// a Done channel for cancellation.
Done() <-chan struct{}
// If Done is not yet closed, Err returns nil.
// If Done is closed, Err returns a non-nil error explaining why:
// Canceled if the context was canceled
// or DeadlineExceeded if the context's deadline passed.
// After Err returns a non-nil error, successive calls to Err return the same error.
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
// 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
// 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;
// packages should define keys as an unexported type to avoid
// collisions.
//
// Packages that define a Context key should provide type-safe accessors
// for the values stored using that key:
//
// // Package user defines a User type that's stored in Contexts.
// package user
//
// import "context"
//
// // User is the type of value stored in the Contexts.
// type User struct {...}
//
// // key is an unexported type for keys defined in this package.
// // This prevents collisions with keys defined in other packages.
// type key int
//
// // 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
//
// // NewContext returns a new Context that carries value u.
// func NewContext(ctx context.Context, u *User) context.Context {
// return context.WithValue(ctx, userKey, u)
// }
//
// // FromContext returns the User value stored in ctx, if any.
// func FromContext(ctx context.Context) (*User, bool) {
// u, ok := ctx.Value(userKey).(*User)
// return u, ok
// }
Value(key interface{}) interface{}
}
// Canceled is the error returned by Context.Err when the context is canceled.
var Canceled = errors.New("context canceled")
// DeadlineExceeded is the error returned by Context.Err when the context's
// deadline passes.
var DeadlineExceeded error = deadlineExceededError{}
type deadlineExceededError struct{}
func (deadlineExceededError) Error() string { return "context deadline exceeded" }
func (deadlineExceededError) Timeout() bool { return true }
func (deadlineExceededError) Temporary() bool { return true }
// 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
func (*emptyCtx) Deadline() (deadline time.Time, ok bool) {
return
}
func (*emptyCtx) Done() <-chan struct{} {
return nil
}
func (*emptyCtx) Err() error {
return nil
}
func (*emptyCtx) Value(key interface{}) interface{} {
return nil
}
func (e *emptyCtx) String() string {
switch e {
case background:
return "context.Background"
case todo:
return "context.TODO"
}
return "unknown empty Context"
}
var (
background = new(emptyCtx)
todo = new(emptyCtx)
)
// 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.
func Background() Context {
return background
}
// 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).
func TODO() Context {
return todo
}
// A CancelFunc tells an operation to abandon its work.
// A CancelFunc does not wait for the work to stop.
// After the first call, subsequent calls to a CancelFunc do nothing.
type CancelFunc func()
// WithCancel returns a copy of parent with 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.
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
c := newCancelCtx(parent)
propagateCancel(parent, &c)
return &c, func() { c.cancel(true, Canceled) }
}
// newCancelCtx returns an initialized cancelCtx.
func newCancelCtx(parent Context) cancelCtx {
return cancelCtx{Context: parent}
}
// propagateCancel arranges for child to be canceled when parent is.
func propagateCancel(parent Context, child canceler) {
if parent.Done() == nil {
return // parent is never canceled
}
if p, ok := parentCancelCtx(parent); ok {
p.mu.Lock()
if p.err != nil {
// parent has already been canceled
child.cancel(false, p.err)
} else {
if p.children == nil {
p.children = make(map[canceler]struct{})
}
p.children[child] = struct{}{}
}
p.mu.Unlock()
} else {
go func() {
select {
case <-parent.Done():
child.cancel(false, parent.Err())
case <-child.Done():
}
}()
}
}
// parentCancelCtx follows a chain of parent references until it finds a
// *cancelCtx. This function understands how each of the concrete types in this
// package represents its parent.
func parentCancelCtx(parent Context) (*cancelCtx, bool) {
for {
switch c := parent.(type) {
case *cancelCtx:
return c, true
case *timerCtx:
return &c.cancelCtx, true
case *valueCtx:
parent = c.Context
default:
return nil, false
}
}
}
// removeChild removes a context from its parent.
func removeChild(parent Context, child canceler) {
p, ok := parentCancelCtx(parent)
if !ok {
return
}
p.mu.Lock()
if p.children != nil {
delete(p.children, child)
}
p.mu.Unlock()
}
// 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{}
}
// closedchan is a reusable closed channel.
var closedchan = make(chan struct{})
func init() {
close(closedchan)
}
// A cancelCtx can be canceled. When canceled, it also cancels any children
// that implement canceler.
type cancelCtx struct {
Context
mu sync.Mutex // protects following fields
done chan struct{} // created lazily, closed by first cancel call
children map[canceler]struct{} // set to nil by the first cancel call
err error // set to non-nil by the first cancel call
}
func (c *cancelCtx) Done() <-chan struct{} {
c.mu.Lock()
if c.done == nil {
c.done = make(chan struct{})
}
d := c.done
c.mu.Unlock()
return d
}
func (c *cancelCtx) Err() error {
c.mu.Lock()
err := c.err
c.mu.Unlock()
return err
}
type stringer interface {
String() string
}
func contextName(c Context) string {
if s, ok := c.(stringer); ok {
return s.String()
}
return reflectlite.TypeOf(c).String()
}
func (c *cancelCtx) String() string {
return contextName(c.Context) + ".WithCancel"
}
// cancel closes c.done, cancels each of c's children, and, if
// removeFromParent is true, removes c from its parent's children.
func (c *cancelCtx) cancel(removeFromParent bool, err error) {
if err == nil {
panic("context: internal error: missing cancel error")
}
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return // already canceled
}
c.err = err
if c.done == nil {
c.done = closedchan
} else {
close(c.done)
}
for child := range c.children {
// NOTE: acquiring the child's lock while holding parent's lock.
child.cancel(false, err)
}
c.children = nil
c.mu.Unlock()
if removeFromParent {
removeChild(c.Context, c)
}
}
// 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
// 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.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) {
if cur, ok := parent.Deadline(); ok && cur.Before(d) {
// The current deadline is already sooner than the new one.
return WithCancel(parent)
}
c := &timerCtx{
cancelCtx: newCancelCtx(parent),
deadline: d,
}
propagateCancel(parent, c)
dur := time.Until(d)
if dur <= 0 {
c.cancel(true, DeadlineExceeded) // deadline has already passed
return c, func() { c.cancel(false, Canceled) }
}
c.mu.Lock()
defer c.mu.Unlock()
if c.err == nil {
c.timer = time.AfterFunc(dur, func() {
c.cancel(true, DeadlineExceeded)
})
}
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
// delegating to cancelCtx.cancel.
type timerCtx struct {
cancelCtx
timer *time.Timer // Under cancelCtx.mu.
deadline time.Time
}
func (c *timerCtx) Deadline() (deadline time.Time, ok bool) {
return c.deadline, true
}
func (c *timerCtx) String() string {
return contextName(c.cancelCtx.Context) + ".WithDeadline(" +
c.deadline.String() + " [" +
time.Until(c.deadline).String() + "])"
}
func (c *timerCtx) cancel(removeFromParent bool, err error) {
c.cancelCtx.cancel(false, err)
if removeFromParent {
// Remove this timerCtx from its parent cancelCtx's children.
removeChild(c.cancelCtx.Context, c)
}
c.mu.Lock()
if c.timer != nil {
c.timer.Stop()
c.timer = nil
}
c.mu.Unlock()
}
// 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:
//
// 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)
// }
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
return WithDeadline(parent, time.Now().Add(timeout))
}
// WithValue returns a copy of parent in which 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.
func WithValue(parent Context, key, val interface{}) Context {
if key == nil {
panic("nil key")
}
if !reflectlite.TypeOf(key).Comparable() {
panic("key is not comparable")
}
return &valueCtx{parent, key, val}
}
// 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
key, val interface{}
}
// stringify tries a bit to stringify v, without using fmt, since we don't
// want context depending on the unicode tables. This is only used by
// *valueCtx.String().
func stringify(v interface{}) string {
switch s := v.(type) {
case stringer:
return s.String()
case string:
return s
}
return "<not Stringer>"
}
func (c *valueCtx) String() string {
return contextName(c.Context) + ".WithValue(type " +
reflectlite.TypeOf(c.key).String() +
", val " + stringify(c.val) + ")"
}
func (c *valueCtx) Value(key interface{}) interface{} {
if c.key == key {
return c.val
}
return c.Context.Value(key)
}
golang 標準庫 1.7 版本引入 context 包, 用於 golang 函數鏈安全的管理和控制.
說真 golang context 實現非常漂亮, 代碼中說明也事無巨細, 整體很賞心悅目.
那我們帶大家巨集觀過一遍 context 設計佈局.
// Context 上下文調用鏈條
type Context interface {
// Deadline 返回是否完成和結束時刻
Deadline() (deadline time.Time, ok bool)
// Done 返回是否完成的阻塞 chan
Done() (done <-chan struct{})
// Err Done 時候儲存 error 信息, Canceled or DeadlineExceeded
Err() (err error)
// Value Context 中獲取 key 的值
Value(key interface{}) (val interface{})
}
// emptyCtx 永遠不會被取消的 context
type emptyCtx int
// cancelCtx 可被取消的 context
type cancelCtx struct { Context ... }
// timerCtx 帶計時器和截止日期的 cancelCtx
type timerCtx struct { cancelCtx ... }
// valueCtx 儲存鍵值對 context
type valueCtx struct {
Context
key, val interface{}
}
可以看出 Context 是個 interface, context.go 中有四種結構實現了 Context interface, 分別
是 emptyCtx, cancelCtx, timerCtx, valueCtx. 細看這類數據結構設計思路, 只記錄父親是誰,
單線聯繫. 可以反著類比普通樹結構只記錄兒子是誰哈哈, 大眾貨居然被玩出❀, 真強.
正文 - context 手寫
廢話不多說, 開始寫代碼. 上面 context.go 文件一把梭哈, 對於初學者還是無從學起的. 我們
這裡按照結構分模式展開書寫,
├── context
│ ├── cancel.go
│ ├── context.go
│ ├── empty.go
│ ├── timer.go
│ ├── value.go
│ └── with.go
讓其看起來好理解些.
context.go
package context
import (
"errors"
"time"
)
// Canceled 取消上下文時 context.Err 返回的錯誤
var Canceled = errors.New("context canceled")
// DeadlineExceeded 上下文超時時候 Context.Err 返回的錯誤
var DeadlineExceeded error = deadlineExceededError{}
type deadlineExceededError struct{}
func (deadlineExceededError) Error() string { return "context deadline exceeded" }
func (deadlineExceededError) Timeout() bool { return true }
func (deadlineExceededError) Temporary() bool { return true }
// Context 上下文調用鏈條
type Context interface {
// Deadline 返回是否完成和結束時刻
Deadline() (deadline time.Time, ok bool)
// Done 返回是否完成的阻塞 chan
Done() (done <-chan struct{})
// Err Done 時候儲存 error 信息, Canceled or DeadlineExceeded
Err() (err error)
// Value Context 中獲取 key 的值
Value(key interface{}) (val interface{})
}
empty.go
package context
import "time"
// emptyCtx 永遠不會被取消的 context
type emptyCtx int
func (*emptyCtx) Deadline() (deadline time.Time, ok bool) { return }
func (*emptyCtx) Done() (done <-chan struct{}) { return }
func (*emptyCtx) Err() (err error) { return }
func (*emptyCtx) Value(key interface{}) (val interface{}) { return }
var (
background = new(emptyCtx)
todo = new(emptyCtx)
)
// String emptyCtx 列印方法
func (e *emptyCtx) String() string {
switch e {
case background:
return "context.Background"
case todo:
return "context.TODO"
}
return "unknown empty Context"
}
// Background 不會被取消的 context, 一般用做頂級 context
func Background() Context {
return background
}
// TODO 當你不知道用什麼 Context 時候, 記住那就用這個
func TODO() Context {
return todo
}
cancel.go
package context
import (
"reflect"
"sync"
)
type stringer interface {
String() string
}
func contextName(c Context) string {
if s, ok := c.(stringer); ok {
return s.String()
}
return reflect.TypeOf(c).String()
}
// canceler 可以直接取消的上下文, 詳情見 *cancelCtx 和 *timerCtx
type canceler interface {
cancel(removeFromParent bool, err error)
Done() (done <-chan struct{})
}
// cancelCtx 可被取消的 context
type cancelCtx struct {
Context
mu sync.Mutex // 互斥鎖保證 goroutine 安全
done chan struct{} // 慢創建, 首次取消才會被調用的開關
children map[canceler]struct{} // 首次 context 取消後待取消的 child context
err error // 首次取消 context 保留的 error
}
func (c *cancelCtx) Done() (done <-chan struct{}) {
c.mu.Lock()
if c.done == nil {
c.done = make(chan struct{})
}
done = c.done
c.mu.Unlock()
return
}
func (c *cancelCtx) Err() (err error) {
c.mu.Lock()
err = c.err
c.mu.Unlock()
return
}
func (c *cancelCtx) String() string {
return contextName(c) + ".WithCancel"
}
// newCancelCtx returns an initialized cancelCtx
func newCancelCtx(parent Context) cancelCtx {
return cancelCtx{Context: parent}
}
(這裡用 "reflect" 標準包來表述 "internal/reflectlite" 內部才能使用的 "reflect" 包)
timer.go
package context
import (
"time"
)
// timerCtx 帶計時器和截止日期的 cancelCtx
type timerCtx struct {
cancelCtx
timer *time.Timer // 依賴 cancelCtx.mu
deadline time.Time // context 截止時間
}
func (c *timerCtx) Deadline() (time.Time, bool) {
return c.deadline, true
}
func (c *timerCtx) String() string {
return contextName(c.cancelCtx.Context) + ".WithDeadline(" + c.deadline.String() + " [" + time.Until(c.deadline).String() + "])"
}
value.go
package context
import "reflect"
// valueCtx 儲存鍵值對 context
type valueCtx struct {
Context
key, val interface{}
}
func (c *valueCtx) Value(key interface{}) interface{} {
if c.key == key {
return c.val
}
return c.Context.Value(key)
}
// stringify tries a bit to stringify v, without using fmt, since we don't
// want context depending on the unicode tables. This is only used by *valueCtx.String()
func stringify(v interface{}) string {
switch s := v.(type) {
case stringer:
return s.String()
case string:
return s
}
return "<not Stringer>"
}
func (c *valueCtx) String() string {
return contextName(c.Context) + ".WithValue(type " + reflect.TypeOf(c.key).String() + ", val " + stringify(c.val) + ")"
}
with.go
package context
import (
"reflect"
"time"
)
// WithValue returns a copy of parent in which the value associated with key is val
func WithValue(parent Context, key, val interface{}) Context {
if key == nil {
panic("nil key")
}
// key 不具備可比性時候, 會引發運行時恐慌 panic
if !reflect.TypeOf(key).Comparable() {
panic("key is not comparable")
}
return &valueCtx{parent, key, val}
}
// parentCancelCtx 獲取 parent CancelCtx
func parentCancelCtx(parent Context) (*cancelCtx, bool) {
for {
switch c := parent.(type) {
case *cancelCtx:
return c, true
case *timerCtx:
return &c.cancelCtx, true
case *valueCtx:
parent = c.Context
default:
return nil, false
}
}
}
// removeChild removes a context from its parent
func removeChild(parent Context, child canceler) {
p, ok := parentCancelCtx(parent)
if !ok {
return
}
p.mu.Lock()
if p.children != nil {
delete(p.children, child)
}
p.mu.Unlock()
}
// closedchan 可重覆使用且已經關閉通道
var closedchan = make(chan struct{})
func init() {
close(closedchan)
}
// cancel cancelCtx 取消操作, 關閉 c.done, 取消每個 child context, removeFromParent is true 從 parent 刪除 child
func (c *cancelCtx) cancel(removeFromParent bool, err error) {
c.mu.Lock()
if c.err != nil {
c.mu.Unlock()
return // already canceled
}
c.err = err
if c.done == nil {
c.done = closedchan
} else {
close(c.done)
}
for child := range c.children {
// NOTE: 保留 parent 鎖, 繼續獲取 child 鎖
child.cancel(false, err)
}
c.children = nil
c.mu.Unlock()
if removeFromParent {
removeChild(c.Context, c)
}
}
// cancel timerCtx 取消操作
func (c *timerCtx) cancel(removeFromParent bool, err error) {
c.cancelCtx.cancel(false, err)
if removeFromParent {
// Remove this timerCtx from its parent cancelCtx's children
removeChild(c.cancelCtx.Context, c)
}
c.mu.Lock()
if c.timer != nil {
c.timer.Stop()
c.timer = nil
}
c.mu.Unlock()
}
// propagateCancel parent 取消 map 中添加 child 子項
func propagateCancel(parent Context, child canceler) {
if parent.Done() == nil {
return // parent is never canceled
}
if p, ok := parentCancelCtx(parent); ok {
p.mu.Lock()
if p.err != nil {
// parent has already been canceled
child.cancel(false, p.err)
} else {
if p.children == nil {
p.children = make(map[canceler]struct{})
}
p.children[child] = struct{}{}
}
p.mu.Unlock()
} else {
go func() {
select {
case <-parent.Done():
child.cancel(false, parent.Err())
case <-child.Done():
}
}()
}
}
// CancelFunc cancel func 行為
type CancelFunc func()
// WithCancel 基於 parent context 構造可取消的 child context
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
c := newCancelCtx(parent)
propagateCancel(parent, &c)
return &c, func() { c.cancel(true, Canceled) }
}
// WithDeadline 返回 child context 並調整 parent deadline
func WithDeadline(parent Context, d time.Time) (Context, CancelFunc) {
if cur, ok := parent.Deadline(); ok && cur.Before(d) {
// 當前截止日期早於新設置的截止日期, 直接使用當前截止日期
return WithCancel(parent)
}
c := &timerCtx{
cancelCtx: newCancelCtx(parent),
deadline: d,
}
propagateCancel(parent, c)
dur := time.Until(d)
if dur <= 0 {
c.cancel(true, DeadlineExceeded) // deadline has already passed
return c, func() { c.cancel(false, Canceled) }
}
c.mu.Lock()
defer c.mu.Unlock()
if c.err == nil {
c.timer = time.AfterFunc(dur, func() {
c.cancel(true, DeadlineExceeded)
})
}
return c, func() { c.cancel(true, Canceled) }
}
// WithTimeout returns WithDeadline(parent, time.Now().Add(timeout))
func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
return WithDeadline(parent, time.Now().Add(timeout))
}
看到 with.go 是不是有種 mmp 感覺, 第一問還好, 第二問也爽爽, 這第三問怎麼就有了壓軸最後一問思索感 ~
其實還好, 多關懷下 propagateCancel 和 cancelCtx.cancel 操作怎麼打配合. 其實上面源碼中最難寫的是
reflect 和 time (errors 和 sync 接觸多好理解) 有興趣的同行可以深入研究 . 水文該說再見了, 希望大家有
所得 ~
後記 - 代碼和註釋並存
錯誤是難免的, 歡迎勘誤 ~ 共同成長提高 ❉
<窗外雨> - https://music.163.com/#/song?id=514543382
