本文包含对context实现上的分析和使用方式，分析部分源码讲解比价多，可能会比较枯燥，读者可以直接跳过去阅读使用部分。
一、简介作者所讲的context的包名称是： "golang.org/x/net/context" ,希望读者不要引用错误了。
在godoc中对context的介绍如下：
Package context defines the Context type, which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes. As of Go 1.7 this package is available in the standard library under the name context. https://golang.org/pkg/context. Incoming requests to a server should create a Context, and outgoing calls to servers should accept a Context. The chain of function calls between must propagate the Context, optionally replacing it with a modified copy created using WithDeadline, WithTimeout, WithCancel, or WithValue. 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 for example code for a server that uses Contexts.