# goroutine 调度时机有哪些

在四种情形下，goroutine 可能会发生调度，但也并不一定会发生，只是说 Go scheduler 有机会进行调度。

| 情形         | 说明                                                                                                                 |
| ---------- | ------------------------------------------------------------------------------------------------------------------ |
| 使用关键字 `go` | go 创建一个新的 goroutine，Go scheduler 会考虑调度                                                                             |
| GC         | 由于进行 GC 的 goroutine 也需要在 M 上运行，因此肯定会发生调度。当然，Go scheduler 还会做很多其他的调度，例如调度不涉及堆访问的 goroutine 来运行。GC 不管栈上的内存，只会回收堆上的内存 |
| 系统调用       | 当 goroutine 进行系统调用时，会阻塞 M，所以它会被调度走，同时一个新的 goroutine 会被调度上来                                                         |
| 内存同步访问     | atomic，mutex，channel 操作等会使 goroutine 阻塞，因此会被调度走。等条件满足后（例如其他 goroutine 解锁了）还会被调度上来继续运行                              |


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