| // Copyright 2016 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_test |
| |
| import ( |
| "context" |
| "fmt" |
| "time" |
| ) |
| |
| // This example demonstrate the use of a cancelable context preventing a |
| // goroutine leak. By the end of the example func's execution, the "count" |
| // goroutine is canceled. |
| func ExampleWithCancel() { |
| count := func(ctx context.Context, dst chan<- int) { |
| n := 1 |
| for { |
| select { |
| case dst <- n: |
| n++ |
| case <-ctx.Done(): |
| return |
| } |
| } |
| } |
| |
| ctx, cancel := context.WithCancel(context.Background()) |
| defer cancel() |
| |
| ints := make(chan int) |
| go count(ctx, ints) |
| for n := range ints { |
| fmt.Println(n) |
| if n == 5 { |
| return |
| } |
| } |
| // Output: |
| // 1 |
| // 2 |
| // 3 |
| // 4 |
| // 5 |
| } |
| |
| // This example passes a context with a arbitrary deadline to tell a blocking |
| // function that it should abandon its work as soon as it gets to it. |
| func ExampleWithDeadline() { |
| d := time.Now().Add(50 * time.Millisecond) |
| ctx, cancel := context.WithDeadline(context.Background(), d) |
| |
| // Even though ctx will be expired, it is good practice to call its |
| // cancelation function in any case. Failure to do so may keep the |
| // context and its parent alive longer than necessary. |
| defer cancel() |
| |
| select { |
| case <-time.After(1 * time.Second): |
| fmt.Println("overslept") |
| case <-ctx.Done(): |
| fmt.Println(ctx.Err()) |
| } |
| |
| // Output: |
| // context deadline exceeded |
| } |
| |
| // This example passes a context with a timeout to tell a blocking function that |
| // it should abandon its work after the timeout elapses. |
| func ExampleWithTimeout() { |
| // Pass a context with a timeout to tell a blocking function that it |
| // should abandon its work after the timeout elapses. |
| ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond) |
| defer cancel() |
| |
| select { |
| case <-time.After(1 * time.Second): |
| fmt.Println("overslept") |
| case <-ctx.Done(): |
| fmt.Println(ctx.Err()) // prints "context deadline exceeded" |
| } |
| |
| // Output: |
| // context deadline exceeded |
| } |
| |
| func ExampleWithValue() { |
| type favContextKey string |
| |
| f := func(ctx context.Context, k favContextKey) { |
| if v := ctx.Value(k); v != nil { |
| fmt.Println("found value:", v) |
| return |
| } |
| fmt.Println("key not found:", k) |
| } |
| |
| k := favContextKey("language") |
| ctx := context.WithValue(context.Background(), k, "Go") |
| |
| f(ctx, k) |
| f(ctx, favContextKey("color")) |
| |
| // Output: |
| // found value: Go |
| // key not found: color |
| } |