时间：2023-02-15 13:15:31 | 栏目：Golang | 点击：次
example_test.go,展示了With-系列的4个例子
func ExampleWithCancel() {
gen := func(ctx context.Context) <-chan int {
dst := make(chan int)
n := 1
go func() {
for {
select {
case <-ctx.Done():
return // returning not to leak the goroutine
case dst <- n:
n++
}
}
}()
return dst
}
ctx, cancel := context.WithCancel(context.Background())
defer cancel() // cancel when we are finished consuming integers
for n := range gen(ctx) {
fmt.Println(n)
if n == 5 {
break
}
}
// Output:
// 1
// 2
// 3
// 4
// 5
}
结构分析,gen是一个函数,返回值是一个信道, for range channel是有特殊意义的, for会循环从channel读数据,直到channel被close(),不然就是无限循环.
gen内部的协程就是典型的闭包,for range会不断触发读,gen内部的for select 会不断触发写,主协程读5次之后,会结束main函数,会触发defer函数, 也就是取消操作对应的回调,此时done信道会被close,gen内部的协程会正常退出.
这个例子是测试支持取消信号的上下文,取消函数的调用放在了main的defer函数中.
const shortDuration = 1 * time.Millisecond
func ExampleWithDeadline() {
d := time.Now().Add(shortDuration)
ctx, cancel := context.WithDeadline(context.Background(), d)
// Even though ctx will be expired, it is good practice to call its
// cancellation 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
}
deadline的这个例子,在main的defer中也有主动调用取消函数的. 实际上通过打印可以显示deadline是否按预期工作.
func ExampleWithTimeout() {
ctx, cancel := context.WithTimeout(context.Background(), shortDuration)
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
}
timeout只是deadline的一种简写.
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
}
context.WithValue和Context.Value()是存取操作, 取的时候,如果key没找到,会返回nil.
context_text.go,x_test.go是单元测试, example_test.go是示例,benchmark_test.go是基准测试, net_test.go展示了deadline对net包的支持.
先看单元测试的context_text.go.
type testingT interface {}
type otherContext struct {}
func quiescent(t testingT) time.Duration {}
func XTestBackground(t testingT) {}
func XTestTODO(t testingT) {}
func XTestWithCancel(t testingT) {}
func contains(m map[canceler]struct{}, key canceler) bool {}
func XTestParentFinishesChild(t testingT) {}
func XTestChildFinishesFirst(t testingT) {}
func testDeadline(c Context, name string, t testingT) {}
func XTestDeadline(t testingT) {}
func XTestTimeout(t testingT) {}
func XTestCanceledTimeout(t testingT) {}
func XTestValues(t testingT) {}
func XTestAllocs(t testingT, testingShort func() bool, testingAllocsPerRun func(int, func()) float64) {}
func XTestSimultaneousCancels(t testingT) {}
func XTestInterlockedCancels(t testingT) {}
func XTestLayersCancel(t testingT) {}
func XTestLayersTimeout(t testingT) {}
func XTestCancelRemoves(t testingT) {}
func XTestWithCancelCanceledParent(t testingT) {}
func XTestWithValueChecksKey(t testingT) {}
func XTestInvalidDerivedFail(t testingT) {}
func recoveredValue(fn func()) (v interface{}) {}
func XTestDeadlineExceededSupportsTimeout(t testingT) {}
type myCtx struct {}
type myDoneCtx struct {}
func (d *myDoneCtx) Done() <-chan struct{} {}
func XTestCustomContextGoroutines(t testingT) {}
这暴露的大多测试函数的参数类型是testingT接口类型,但这个源文件中没有实现testingT接口的,
func TestBackground(t *testing.T) { XTestBackground(t) }
func TestTODO(t *testing.T) { XTestTODO(t) }
func TestWithCancel(t *testing.T) { XTestWithCancel(t) }
func TestParentFinishesChild(t *testing.T) { XTestParentFinishesChild(t) }
func TestChildFinishesFirst(t *testing.T) { XTestChildFinishesFirst(t) }
func TestDeadline(t *testing.T) { XTestDeadline(t) }
func TestTimeout(t *testing.T) { XTestTimeout(t) }
func TestCanceledTimeout(t *testing.T) { XTestCanceledTimeout(t) }
func TestValues(t *testing.T) { XTestValues(t) }
func TestAllocs(t *testing.T) { XTestAllocs(t, testing.Short, testing.AllocsPerRun) }
func TestSimultaneousCancels(t *testing.T) { XTestSimultaneousCancels(t) }
func TestInterlockedCancels(t *testing.T) { XTestInterlockedCancels(t) }
func TestLayersCancel(t *testing.T) { XTestLayersCancel(t) }
func TestLayersTimeout(t *testing.T) { XTestLayersTimeout(t) }
func TestCancelRemoves(t *testing.T) { XTestCancelRemoves(t) }
func TestWithCancelCanceledParent(t *testing.T) { XTestWithCancelCanceledParent(t) }
func TestWithValueChecksKey(t *testing.T) { XTestWithValueChecksKey(t) }
func TestInvalidDerivedFail(t *testing.T) { XTestInvalidDerivedFail(t) }
func TestDeadlineExceededSupportsTimeout(t *testing.T) { XTestDeadlineExceededSupportsTimeout(t) }
func TestCustomContextGoroutines(t *testing.T) { XTestCustomContextGoroutines(t) }
这是x_test.go的内容,直接是用testing.T类型来实现testingT接口.
那先分析一下testing.T对testingT接口的实现.
type T struct {
common
isParallel bool
context *testContext
}
func (t *T) Deadline() (deadline time.Time, ok bool) {
deadline = t.context.deadline
return deadline, !deadline.IsZero()
}
注意：testing.T.context不是context.Context的实现类型, Deadline()返回了t.context中存储的deadline信息.
testing.T内嵌了testing.common,大部分方法集都来至common:
Error(args ...interface{})
Errorf(format string, args ...interface{})
Fail()
FailNow()
Failed() bool
Fatal(args ...interface{})
Fatalf(format string, args ...interface{})
Helper()
Log(args ...interface{})
Logf(format string, args ...interface{})
Name() string
Skip(args ...interface{})
SkipNow()
Skipf(format string, args ...interface{})
Skipped() bool
Parallel()是由testing.T实现,某个测试用例多次重复执行时, 可启用并发参数.