Question

标准库里与调度相关的几个函数。了解实现细节，以便放心使用。

runtime.Gosched

让出当前 G 执行绪。与 gopark 的区别，G 会被放回队列，无需 goready 唤醒。

// proc.go

// Gosched yields the processor, allowing other goroutines to run. It does not
// suspend the current goroutine, so execution resumes automatically.
func Gosched() {
	mcall(gosched_m)
}

// Gosched continuation on g0.
func gosched_m(gp *g) {
	goschedImpl(gp)
}

func goschedImpl(gp *g) {
    
    // 修改状态。
	status := readgstatus(gp)
	if status&^_Gscan != _Grunning {
		dumpgstatus(gp)
		throw("bad g status")
	}
	casgstatus(gp, _Grunning, _Grunnable)
    
    // 解除 MP 绑定，放回全局队列。
	dropg()
	lock(&sched.lock)
	globrunqput(gp)
	unlock(&sched.lock)

    // 当前 MP 执行其他任务。
	schedule()
}

runtime.Goexit

终止当前任务。这与 return 返回调用堆栈上一级不同，而是直接结束整个任务。

在 Main Goroutine 调用 Goexit，它会等待其他 Gs 结束后才会崩溃。

注意，终止的是 G 函数执行，而不是 MP。

// panic.go

// Goexit terminates the goroutine that calls it. No other goroutine is affected.
// Goexit runs all deferred calls before terminating the goroutine. Because Goexit
// is not a panic, any recover calls in those deferred functions will return nil.
//
// Calling Goexit from the main goroutine terminates that goroutine
// without func main returning. Since func main has not returned,
// the program continues execution of other goroutines.
// If all other goroutines exit, the program crashes.

func Goexit() {
    
    // panic, defer ...
    
	goexit1()
}

// proc.go

// Finishes execution of the current goroutine.
func goexit1() {
	mcall(goexit0)
}

// goexit continuation on g0.
func goexit0(gp *g) {
	
    // G 任务结束，清理后放回复用链表。
    casgstatus(gp, _Grunning, _Gdead)
	dropg()
	gfput(_p_, gp)
    
    // 当前 MP 继续执行其他任务。
	schedule()
}