目录
背景
golangchannelchannelgoroutinechannelchannelchannel准备好准备好
1.发送
channelgoroutine
2.接收
channelgoroutine
channelselect
channelchannel
select 流程
selectgoroutinefor{}goroutineselect{}goroutine
if len(cases) == 0 { block() }
channelchannelselectchannelchannelchannel
// generate permuted order norder := 0 for i := range scases { cas := &scases[i] // Omit cases without channels from the poll and lock orders. if cas.c == nil { cas.elem = nil // allow GC continue } j := fastrandn(uint32(norder + 1)) pollorder[norder] = pollorder[j] pollorder[j] = uint16(i) norder++ }
channelchannelchannel channelchannelselectselectchannelselect
selectchannelchannelchannelselectchannelchannelchannel
channelchannel
// sort the cases by Hchan address to get the locking order. // simple heap sort, to guarantee n log n time and constant stack footprint. for i := range lockorder { j := i // Start with the pollorder to permute cases on the same channel. c := scases[pollorder[i]].c for j > 0 && scases[lockorder[(j-1)/2]].c.sortkey() < c.sortkey() { k := (j - 1) / 2 lockorder[j] = lockorder[k] j = k } lockorder[j] = pollorder[i] } for i := len(lockorder) - 1; i >= 0; i-- { o := lockorder[i] c := scases[o].c lockorder[i] = lockorder[0] j := 0 for { k := j*2 + 1 if k >= i { break } if k+1 < i && scases[lockorder[k]].c.sortkey() < scases[lockorder[k+1]].c.sortkey() { k++ } if c.sortkey() < scases[lockorder[k]].c.sortkey() { lockorder[j] = lockorder[k] j = k continue } break } lockorder[j] = o }
selectchannelchannel
// lock all the channels involved in the select sellock(scases, lockorder)
准备好channelchannelselectchannelchannelchannel
pollorderchannel
for _, casei := range pollorder { casi = int(casei) cas = &scases[casi] c = cas.c if casi >= nsends { sg = c.sendq.dequeue() if sg != nil { goto recv } if c.qcount > 0 { goto bufrecv } if c.closed != 0 { goto rclose } } else { if raceenabled { racereadpc(c.raceaddr(), casePC(casi), chansendpc) } if c.closed != 0 { goto sclose } sg = c.recvq.dequeue() if sg != nil { goto send } if c.qcount < c.dataqsiz { goto bufsend } } }
default
if !block { selunlock(scases, lockorder) casi = -1 goto retc }
channelsudoggoroutinechannelchannel
// pass 2 - enqueue on all chans gp = getg() if gp.waiting != nil { throw("gp.waiting != nil") } nextp = &gp.waiting for _, casei := range lockorder { casi = int(casei) cas = &scases[casi] c = cas.c sg := acquireSudog() sg.g = gp sg.isSelect = true // No stack splits between assigning elem and enqueuing // sg on gp.waiting where copystack can find it. sg.elem = cas.elem sg.releasetime = 0 if t0 != 0 { sg.releasetime = -1 } sg.c = c // Construct waiting list in lock order. *nextp = sg nextp = &sg.waitlink if casi < nsends { c.sendq.enqueue(sg) } else { c.recvq.enqueue(sg) } }
goparkchannel
// wait for someone to wake us up gp.param = nil // Signal to anyone trying to shrink our stack that we're about // to park on a channel. The window between when this G's status // changes and when we set gp.activeStackChans is not safe for // stack shrinking. atomic.Store8(&gp.parkingOnChan, 1) gopark(selparkcommit, nil, waitReasonSelect, traceEvGoBlockSelect, 1) gp.activeStackChans = false
9.被唤醒
channelgoroutinesudogchannelchannelgoroutinesudog
sellock(scases, lockorder) gp.selectDone = 0 sg = (*sudog)(gp.param) gp.param = nil // pass 3 - dequeue from unsuccessful chans // otherwise they stack up on quiet channels // record the successful case, if any. // We singly-linked up the SudoGs in lock order. casi = -1 cas = nil caseSuccess = false sglist = gp.waiting // Clear all elem before unlinking from gp.waiting. for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink { sg1.isSelect = false sg1.elem = nil sg1.c = nil } gp.waiting = nil for _, casei := range lockorder { k = &scases[casei] if sg == sglist { // sg has already been dequeued by the G that woke us up. casi = int(casei) cas = k caseSuccess = sglist.success if sglist.releasetime > 0 { caseReleaseTime = sglist.releasetime } } else { c = k.c if int(casei) < nsends { c.sendq.dequeueSudoG(sglist) } else { c.recvq.dequeueSudoG(sglist) } } sgnext = sglist.waitlink sglist.waitlink = nil releaseSudog(sglist) sglist = sgnext }
您可能感兴趣的文章: