selectgo loop

selectgo_loop.go

func selectgo(cas0 *scase, order0 *uint16, ncases int) (int, bool) {
	// ...
loop:
	// ...
	for i := 0; i < ncases; i++ {
		casi = int(pollorder[i])
		cas = &scases[casi]
		c = cas.c

		switch cas.kind {
		case caseNil:
			continue

		case caseRecv:
			sg = c.sendq.dequeue()
			if sg != nil {
				goto recv
			}
			if c.qcount > 0 {
				goto bufrecv
			}
			if c.closed != 0 {
				goto rclose
			}

		case caseSend:
			if c.closed != 0 {
				goto sclose
			}
			sg = c.recvq.dequeue()
			if sg != nil {
				goto send
			}
			if c.qcount < c.dataqsiz {
				goto bufsend
			}

		case caseDefault:
			dfli = casi
			dfl = cas
		}
	}

	if dfl != nil {
		selunlock(scases, lockorder)
		casi = dfli
		cas = dfl
		goto retc
	}

	// ...
}

浅谈 Go 语言 select 的实现原理