源代码与测试代码 https://github.com/YJZhangChina/GNP/tree/master/basic 下 goroutine_traps.go 与 goroutine_traps_test.go

1. 不安全的指针传递

Goroutine的调度次序未知，如果执行多次有指针传递的函数，且函数内存在写操作，需要考虑脏读和原子性问题。定义了Message结构体存储当前值current，valueChange方法用于修改current为当前步骤数step，并用Message指导后续操作。多次运goroutine执行该方法，由于指针传递，Message实例仅有一份，goroutine无法保证函数流程的原子性，造成了写无效和脏读。适当增大循环次数size可更容易发现该问题。

Testing UnsafePointerPassing in GoroutineTraps // 模拟结果可能不同After step 9 the value is 9. After step 0 the value is 0. After step 1 the value is 1. After step 2 the value is 2. After step 3 the value is 3. After step 4 the value is 4. After step 7 the value is 7. After step 8 the value is 8. After step 5 the value is 5. After step 6 the value is 5. // Error

指针传递前对Message实例进行克隆，产生写时复制的效果，修改后的结果不受影响。

Testing SafePointerPassing in GoroutineTraps // 模拟结果可能不同After step 0 the value is 0.After step 9 the value is 9.After step 5 the value is 5.After step 6 the value is 6.After step 7 the value is 7.After step 8 the value is 8.After step 2 the value is 2.After step 1 the value is 1.After step 3 the value is 3.After step 4 the value is 4.

goroutine_traps.go

package basicimport (	"fmt"	"sync")type Message struct {	current int}func valueChange(step int, message *Message, waiter *sync.WaitGroup) {	message.current = step	fmt.Printf("After step %d the value is %d.\n", step, message.current)	waiter.Done()}

goroutine_traps_test.go

package basicimport (	"fmt"	"sync"	"testing")func TestUnsafePointerPassing(t *testing.T) {	fmt.Println("Testing UnsafePointerPassing in GoroutineTraps")	size := 10	var waiter sync.WaitGroup	waiter.Add(size)	message := &Message{current: 1}	for i := 0; i < size; i++ {		go valueChange(i+1, message, &waiter)	}	waiter.Wait()}func TestSafePointerPassing(t *testing.T) {	fmt.Println("Testing SafePointerPassing in GoroutineTraps")	size := 10	var waiter sync.WaitGroup	waiter.Add(size)	message := &Message{current: 1}	for i := 0; i < 10; i++ {		var clone = new(Message)		*clone = *message		go valueChange(i+1, clone, &waiter)	}	waiter.Wait()}