summaryrefslogtreecommitdiff
path: root/libgo/go/runtime/select.go
diff options
context:
space:
mode:
Diffstat (limited to 'libgo/go/runtime/select.go')
-rw-r--r--libgo/go/runtime/select.go651
1 files changed, 651 insertions, 0 deletions
diff --git a/libgo/go/runtime/select.go b/libgo/go/runtime/select.go
new file mode 100644
index 0000000000..f735a71e2f
--- /dev/null
+++ b/libgo/go/runtime/select.go
@@ -0,0 +1,651 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+// This file contains the implementation of Go select statements.
+
+import "unsafe"
+
+const (
+ debugSelect = false
+)
+
+var (
+ chansendpc = funcPC(chansend)
+ chanrecvpc = funcPC(chanrecv)
+)
+
+func selectsize(size uintptr) uintptr {
+ selsize := unsafe.Sizeof(_select{}) +
+ (size-1)*unsafe.Sizeof(_select{}.scase[0]) +
+ size*unsafe.Sizeof(*_select{}.lockorder) +
+ size*unsafe.Sizeof(*_select{}.pollorder)
+ return round(selsize, _Int64Align)
+}
+
+func newselect(sel *_select, selsize int64, size int32) {
+ if selsize != int64(selectsize(uintptr(size))) {
+ print("runtime: bad select size ", selsize, ", want ", selectsize(uintptr(size)), "\n")
+ gothrow("bad select size")
+ }
+ sel.tcase = uint16(size)
+ sel.ncase = 0
+ sel.lockorder = (**hchan)(add(unsafe.Pointer(&sel.scase), uintptr(size)*unsafe.Sizeof(_select{}.scase[0])))
+ sel.pollorder = (*uint16)(add(unsafe.Pointer(sel.lockorder), uintptr(size)*unsafe.Sizeof(*_select{}.lockorder)))
+
+ if debugSelect {
+ print("newselect s=", sel, " size=", size, "\n")
+ }
+}
+
+//go:nosplit
+func selectsend(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
+ // nil cases do not compete
+ if c != nil {
+ selectsendImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+ }
+ return
+}
+
+// cut in half to give stack a chance to split
+func selectsendImpl(sel *_select, c *hchan, pc uintptr, elem unsafe.Pointer, so uintptr) {
+ i := sel.ncase
+ if i >= sel.tcase {
+ gothrow("selectsend: too many cases")
+ }
+ sel.ncase = i + 1
+ cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+
+ cas.pc = pc
+ cas._chan = c
+ cas.so = uint16(so)
+ cas.kind = _CaseSend
+ cas.elem = elem
+
+ if debugSelect {
+ print("selectsend s=", sel, " pc=", hex(cas.pc), " chan=", cas._chan, " so=", cas.so, "\n")
+ }
+}
+
+//go:nosplit
+func selectrecv(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
+ // nil cases do not compete
+ if c != nil {
+ selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, nil, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+ }
+ return
+}
+
+//go:nosplit
+func selectrecv2(sel *_select, c *hchan, elem unsafe.Pointer, received *bool) (selected bool) {
+ // nil cases do not compete
+ if c != nil {
+ selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, received, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+ }
+ return
+}
+
+func selectrecvImpl(sel *_select, c *hchan, pc uintptr, elem unsafe.Pointer, received *bool, so uintptr) {
+ i := sel.ncase
+ if i >= sel.tcase {
+ gothrow("selectrecv: too many cases")
+ }
+ sel.ncase = i + 1
+ cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+ cas.pc = pc
+ cas._chan = c
+ cas.so = uint16(so)
+ cas.kind = _CaseRecv
+ cas.elem = elem
+ cas.receivedp = received
+
+ if debugSelect {
+ print("selectrecv s=", sel, " pc=", hex(cas.pc), " chan=", cas._chan, " so=", cas.so, "\n")
+ }
+}
+
+//go:nosplit
+func selectdefault(sel *_select) (selected bool) {
+ selectdefaultImpl(sel, getcallerpc(unsafe.Pointer(&sel)), uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+ return
+}
+
+func selectdefaultImpl(sel *_select, callerpc uintptr, so uintptr) {
+ i := sel.ncase
+ if i >= sel.tcase {
+ gothrow("selectdefault: too many cases")
+ }
+ sel.ncase = i + 1
+ cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+ cas.pc = callerpc
+ cas._chan = nil
+ cas.so = uint16(so)
+ cas.kind = _CaseDefault
+
+ if debugSelect {
+ print("selectdefault s=", sel, " pc=", hex(cas.pc), " so=", cas.so, "\n")
+ }
+}
+
+func sellock(sel *_select) {
+ lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
+ lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+ var c *hchan
+ for _, c0 := range lockorder {
+ if c0 != nil && c0 != c {
+ c = c0
+ lock(&c.lock)
+ }
+ }
+}
+
+func selunlock(sel *_select) {
+ // We must be very careful here to not touch sel after we have unlocked
+ // the last lock, because sel can be freed right after the last unlock.
+ // Consider the following situation.
+ // First M calls runtime·park() in runtime·selectgo() passing the sel.
+ // Once runtime·park() has unlocked the last lock, another M makes
+ // the G that calls select runnable again and schedules it for execution.
+ // When the G runs on another M, it locks all the locks and frees sel.
+ // Now if the first M touches sel, it will access freed memory.
+ n := int(sel.ncase)
+ r := 0
+ lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), n, n}
+ lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+ // skip the default case
+ if n > 0 && lockorder[0] == nil {
+ r = 1
+ }
+ for i := n - 1; i >= r; i-- {
+ c := lockorder[i]
+ if i > 0 && c == lockorder[i-1] {
+ continue // will unlock it on the next iteration
+ }
+ unlock(&c.lock)
+ }
+}
+
+func selparkcommit(gp *g, sel *_select) bool {
+ selunlock(sel)
+ return true
+}
+
+func block() {
+ gopark(nil, nil, "select (no cases)") // forever
+}
+
+// overwrites return pc on stack to signal which case of the select
+// to run, so cannot appear at the top of a split stack.
+//go:nosplit
+func selectgo(sel *_select) {
+ pc, offset := selectgoImpl(sel)
+ *(*bool)(add(unsafe.Pointer(&sel), uintptr(offset))) = true
+ setcallerpc(unsafe.Pointer(&sel), pc)
+}
+
+// selectgoImpl returns scase.pc and scase.so for the select
+// case which fired.
+func selectgoImpl(sel *_select) (uintptr, uint16) {
+ if debugSelect {
+ print("select: sel=", sel, "\n")
+ }
+
+ scaseslice := sliceStruct{unsafe.Pointer(&sel.scase), int(sel.ncase), int(sel.ncase)}
+ scases := *(*[]scase)(unsafe.Pointer(&scaseslice))
+
+ var t0 int64
+ if blockprofilerate > 0 {
+ t0 = cputicks()
+ for i := 0; i < int(sel.ncase); i++ {
+ scases[i].releasetime = -1
+ }
+ }
+
+ // The compiler rewrites selects that statically have
+ // only 0 or 1 cases plus default into simpler constructs.
+ // The only way we can end up with such small sel.ncase
+ // values here is for a larger select in which most channels
+ // have been nilled out. The general code handles those
+ // cases correctly, and they are rare enough not to bother
+ // optimizing (and needing to test).
+
+ // generate permuted order
+ pollslice := sliceStruct{unsafe.Pointer(sel.pollorder), int(sel.ncase), int(sel.ncase)}
+ pollorder := *(*[]uint16)(unsafe.Pointer(&pollslice))
+ for i := 0; i < int(sel.ncase); i++ {
+ pollorder[i] = uint16(i)
+ }
+ for i := 1; i < int(sel.ncase); i++ {
+ o := pollorder[i]
+ j := int(fastrand1()) % (i + 1)
+ pollorder[i] = pollorder[j]
+ pollorder[j] = o
+ }
+
+ // sort the cases by Hchan address to get the locking order.
+ // simple heap sort, to guarantee n log n time and constant stack footprint.
+ lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
+ lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+ for i := 0; i < int(sel.ncase); i++ {
+ j := i
+ c := scases[j]._chan
+ for j > 0 && lockorder[(j-1)/2].sortkey() < c.sortkey() {
+ k := (j - 1) / 2
+ lockorder[j] = lockorder[k]
+ j = k
+ }
+ lockorder[j] = c
+ }
+ for i := int(sel.ncase) - 1; i >= 0; i-- {
+ c := lockorder[i]
+ lockorder[i] = lockorder[0]
+ j := 0
+ for {
+ k := j*2 + 1
+ if k >= i {
+ break
+ }
+ if k+1 < i && lockorder[k].sortkey() < lockorder[k+1].sortkey() {
+ k++
+ }
+ if c.sortkey() < lockorder[k].sortkey() {
+ lockorder[j] = lockorder[k]
+ j = k
+ continue
+ }
+ break
+ }
+ lockorder[j] = c
+ }
+ /*
+ for i := 0; i+1 < int(sel.ncase); i++ {
+ if lockorder[i].sortkey() > lockorder[i+1].sortkey() {
+ print("i=", i, " x=", lockorder[i], " y=", lockorder[i+1], "\n")
+ gothrow("select: broken sort")
+ }
+ }
+ */
+
+ // lock all the channels involved in the select
+ sellock(sel)
+
+ var (
+ gp *g
+ done uint32
+ sg *sudog
+ c *hchan
+ k *scase
+ sglist *sudog
+ sgnext *sudog
+ )
+
+loop:
+ // pass 1 - look for something already waiting
+ var dfl *scase
+ var cas *scase
+ for i := 0; i < int(sel.ncase); i++ {
+ cas = &scases[pollorder[i]]
+ c = cas._chan
+
+ switch cas.kind {
+ case _CaseRecv:
+ if c.dataqsiz > 0 {
+ if c.qcount > 0 {
+ goto asyncrecv
+ }
+ } else {
+ sg = c.sendq.dequeue()
+ if sg != nil {
+ goto syncrecv
+ }
+ }
+ if c.closed != 0 {
+ goto rclose
+ }
+
+ case _CaseSend:
+ if raceenabled {
+ racereadpc(unsafe.Pointer(c), cas.pc, chansendpc)
+ }
+ if c.closed != 0 {
+ goto sclose
+ }
+ if c.dataqsiz > 0 {
+ if c.qcount < c.dataqsiz {
+ goto asyncsend
+ }
+ } else {
+ sg = c.recvq.dequeue()
+ if sg != nil {
+ goto syncsend
+ }
+ }
+
+ case _CaseDefault:
+ dfl = cas
+ }
+ }
+
+ if dfl != nil {
+ selunlock(sel)
+ cas = dfl
+ goto retc
+ }
+
+ // pass 2 - enqueue on all chans
+ gp = getg()
+ done = 0
+ for i := 0; i < int(sel.ncase); i++ {
+ cas = &scases[pollorder[i]]
+ c = cas._chan
+ sg := acquireSudog()
+ sg.g = gp
+ // Note: selectdone is adjusted for stack copies in stack.c:adjustsudogs
+ sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done)))
+ sg.elem = cas.elem
+ sg.releasetime = 0
+ if t0 != 0 {
+ sg.releasetime = -1
+ }
+ sg.waitlink = gp.waiting
+ gp.waiting = sg
+
+ switch cas.kind {
+ case _CaseRecv:
+ c.recvq.enqueue(sg)
+
+ case _CaseSend:
+ c.sendq.enqueue(sg)
+ }
+ }
+
+ // wait for someone to wake us up
+ gp.param = nil
+ gopark(unsafe.Pointer(funcPC(selparkcommit)), unsafe.Pointer(sel), "select")
+
+ // someone woke us up
+ sellock(sel)
+ 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 case order, so when
+ // iterating through the linked list they are in reverse order.
+ cas = nil
+ sglist = gp.waiting
+ // Clear all selectdone and elem before unlinking from gp.waiting.
+ // They must be cleared before being put back into the sudog cache.
+ // Clear before unlinking, because if a stack copy happens after the unlink,
+ // they will not be updated, they will be left pointing to the old stack,
+ // which creates dangling pointers, which may be detected by the
+ // garbage collector.
+ for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink {
+ sg1.selectdone = nil
+ sg1.elem = nil
+ }
+ gp.waiting = nil
+ for i := int(sel.ncase) - 1; i >= 0; i-- {
+ k = &scases[pollorder[i]]
+ if sglist.releasetime > 0 {
+ k.releasetime = sglist.releasetime
+ }
+ if sg == sglist {
+ cas = k
+ } else {
+ c = k._chan
+ if k.kind == _CaseSend {
+ c.sendq.dequeueSudoG(sglist)
+ } else {
+ c.recvq.dequeueSudoG(sglist)
+ }
+ }
+ sgnext = sglist.waitlink
+ sglist.waitlink = nil
+ releaseSudog(sglist)
+ sglist = sgnext
+ }
+
+ if cas == nil {
+ goto loop
+ }
+
+ c = cas._chan
+
+ if c.dataqsiz > 0 {
+ gothrow("selectgo: shouldn't happen")
+ }
+
+ if debugSelect {
+ print("wait-return: sel=", sel, " c=", c, " cas=", cas, " kind=", cas.kind, "\n")
+ }
+
+ if cas.kind == _CaseRecv {
+ if cas.receivedp != nil {
+ *cas.receivedp = true
+ }
+ }
+
+ if raceenabled {
+ if cas.kind == _CaseRecv && cas.elem != nil {
+ raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+ } else if cas.kind == _CaseSend {
+ raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+ }
+ }
+
+ selunlock(sel)
+ goto retc
+
+asyncrecv:
+ // can receive from buffer
+ if raceenabled {
+ if cas.elem != nil {
+ raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+ }
+ raceacquire(chanbuf(c, c.recvx))
+ racerelease(chanbuf(c, c.recvx))
+ }
+ if cas.receivedp != nil {
+ *cas.receivedp = true
+ }
+ if cas.elem != nil {
+ memmove(cas.elem, chanbuf(c, c.recvx), uintptr(c.elemsize))
+ }
+ memclr(chanbuf(c, c.recvx), uintptr(c.elemsize))
+ c.recvx++
+ if c.recvx == c.dataqsiz {
+ c.recvx = 0
+ }
+ c.qcount--
+ sg = c.sendq.dequeue()
+ if sg != nil {
+ gp = sg.g
+ selunlock(sel)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ } else {
+ selunlock(sel)
+ }
+ goto retc
+
+asyncsend:
+ // can send to buffer
+ if raceenabled {
+ raceacquire(chanbuf(c, c.sendx))
+ racerelease(chanbuf(c, c.sendx))
+ raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+ }
+ memmove(chanbuf(c, c.sendx), cas.elem, uintptr(c.elemsize))
+ c.sendx++
+ if c.sendx == c.dataqsiz {
+ c.sendx = 0
+ }
+ c.qcount++
+ sg = c.recvq.dequeue()
+ if sg != nil {
+ gp = sg.g
+ selunlock(sel)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ } else {
+ selunlock(sel)
+ }
+ goto retc
+
+syncrecv:
+ // can receive from sleeping sender (sg)
+ if raceenabled {
+ if cas.elem != nil {
+ raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+ }
+ racesync(c, sg)
+ }
+ selunlock(sel)
+ if debugSelect {
+ print("syncrecv: sel=", sel, " c=", c, "\n")
+ }
+ if cas.receivedp != nil {
+ *cas.receivedp = true
+ }
+ if cas.elem != nil {
+ memmove(cas.elem, sg.elem, uintptr(c.elemsize))
+ }
+ sg.elem = nil
+ gp = sg.g
+ gp.param = unsafe.Pointer(sg)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+ goto retc
+
+rclose:
+ // read at end of closed channel
+ selunlock(sel)
+ if cas.receivedp != nil {
+ *cas.receivedp = false
+ }
+ if cas.elem != nil {
+ memclr(cas.elem, uintptr(c.elemsize))
+ }
+ if raceenabled {
+ raceacquire(unsafe.Pointer(c))
+ }
+ goto retc
+
+syncsend:
+ // can send to sleeping receiver (sg)
+ if raceenabled {
+ raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+ racesync(c, sg)
+ }
+ selunlock(sel)
+ if debugSelect {
+ print("syncsend: sel=", sel, " c=", c, "\n")
+ }
+ if sg.elem != nil {
+ memmove(sg.elem, cas.elem, uintptr(c.elemsize))
+ }
+ sg.elem = nil
+ gp = sg.g
+ gp.param = unsafe.Pointer(sg)
+ if sg.releasetime != 0 {
+ sg.releasetime = cputicks()
+ }
+ goready(gp)
+
+retc:
+ if cas.releasetime > 0 {
+ blockevent(cas.releasetime-t0, 2)
+ }
+ return cas.pc, cas.so
+
+sclose:
+ // send on closed channel
+ selunlock(sel)
+ panic("send on closed channel")
+}
+
+func (c *hchan) sortkey() uintptr {
+ // TODO(khr): if we have a moving garbage collector, we'll need to
+ // change this function.
+ return uintptr(unsafe.Pointer(c))
+}
+
+// A runtimeSelect is a single case passed to rselect.
+// This must match ../reflect/value.go:/runtimeSelect
+type runtimeSelect struct {
+ dir selectDir
+ typ unsafe.Pointer // channel type (not used here)
+ ch *hchan // channel
+ val unsafe.Pointer // ptr to data (SendDir) or ptr to receive buffer (RecvDir)
+}
+
+// These values must match ../reflect/value.go:/SelectDir.
+type selectDir int
+
+const (
+ _ selectDir = iota
+ selectSend // case Chan <- Send
+ selectRecv // case <-Chan:
+ selectDefault // default
+)
+
+func reflect_rselect(cases []runtimeSelect) (chosen int, recvOK bool) {
+ // flagNoScan is safe here, because all objects are also referenced from cases.
+ size := selectsize(uintptr(len(cases)))
+ sel := (*_select)(mallocgc(size, nil, flagNoScan))
+ newselect(sel, int64(size), int32(len(cases)))
+ r := new(bool)
+ for i := range cases {
+ rc := &cases[i]
+ switch rc.dir {
+ case selectDefault:
+ selectdefaultImpl(sel, uintptr(i), 0)
+ case selectSend:
+ if rc.ch == nil {
+ break
+ }
+ selectsendImpl(sel, rc.ch, uintptr(i), rc.val, 0)
+ case selectRecv:
+ if rc.ch == nil {
+ break
+ }
+ selectrecvImpl(sel, rc.ch, uintptr(i), rc.val, r, 0)
+ }
+ }
+
+ pc, _ := selectgoImpl(sel)
+ chosen = int(pc)
+ recvOK = *r
+ return
+}
+
+func (q *waitq) dequeueSudoG(s *sudog) {
+ var prevsgp *sudog
+ l := &q.first
+ for {
+ sgp := *l
+ if sgp == nil {
+ return
+ }
+ if sgp == s {
+ *l = sgp.next
+ if q.last == sgp {
+ q.last = prevsgp
+ }
+ s.next = nil
+ return
+ }
+ l = &sgp.next
+ prevsgp = sgp
+ }
+}
View Lorry Controller Status