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https://github.com/autc04/Retro68.git
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759 lines
20 KiB
Go
759 lines
20 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package runtime
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// This file contains the implementation of Go select statements.
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import (
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"runtime/internal/sys"
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"unsafe"
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)
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// For gccgo, use go:linkname to rename compiler-called functions to
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// themselves, so that the compiler will export them.
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//
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//go:linkname newselect runtime.newselect
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//go:linkname selectdefault runtime.selectdefault
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//go:linkname selectsend runtime.selectsend
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//go:linkname selectrecv runtime.selectrecv
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//go:linkname selectrecv2 runtime.selectrecv2
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//go:linkname selectgo runtime.selectgo
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const (
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debugSelect = false
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// scase.kind
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caseRecv = iota
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caseSend
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caseDefault
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)
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// Select statement header.
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// Known to compiler.
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// Changes here must also be made in src/cmd/internal/gc/select.go's selecttype.
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type hselect struct {
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tcase uint16 // total count of scase[]
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ncase uint16 // currently filled scase[]
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pollorder *uint16 // case poll order
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lockorder *uint16 // channel lock order
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scase [1]scase // one per case (in order of appearance)
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}
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// Select case descriptor.
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// Known to compiler.
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// Changes here must also be made in src/cmd/internal/gc/select.go's selecttype.
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type scase struct {
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elem unsafe.Pointer // data element
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c *hchan // chan
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pc uintptr // return pc
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kind uint16
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index uint16 // case index
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receivedp *bool // pointer to received bool (recv2)
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releasetime int64
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}
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var (
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chansendpc = funcPC(chansend)
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chanrecvpc = funcPC(chanrecv)
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)
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func selectsize(size uintptr) uintptr {
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selsize := unsafe.Sizeof(hselect{}) +
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(size-1)*unsafe.Sizeof(hselect{}.scase[0]) +
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size*unsafe.Sizeof(*hselect{}.lockorder) +
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size*unsafe.Sizeof(*hselect{}.pollorder)
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return round(selsize, sys.Int64Align)
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}
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func newselect(sel *hselect, selsize int64, size int32) {
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if selsize != int64(selectsize(uintptr(size))) {
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print("runtime: bad select size ", selsize, ", want ", selectsize(uintptr(size)), "\n")
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throw("bad select size")
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}
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if size != int32(uint16(size)) {
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throw("select size too large")
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}
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sel.tcase = uint16(size)
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sel.ncase = 0
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sel.lockorder = (*uint16)(add(unsafe.Pointer(&sel.scase), uintptr(size)*unsafe.Sizeof(hselect{}.scase[0])))
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sel.pollorder = (*uint16)(add(unsafe.Pointer(sel.lockorder), uintptr(size)*unsafe.Sizeof(*hselect{}.lockorder)))
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// For gccgo the temporary variable will not have been zeroed.
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memclrNoHeapPointers(unsafe.Pointer(&sel.scase), uintptr(size)*unsafe.Sizeof(hselect{}.scase[0])+uintptr(size)*unsafe.Sizeof(*hselect{}.lockorder)+uintptr(size)*unsafe.Sizeof(*hselect{}.pollorder))
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if debugSelect {
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print("newselect s=", sel, " size=", size, "\n")
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}
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}
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func selectsend(sel *hselect, c *hchan, elem unsafe.Pointer, index int32) {
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// nil cases do not compete
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if c != nil {
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selectsendImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, index)
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}
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return
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}
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// cut in half to give stack a chance to split
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func selectsendImpl(sel *hselect, c *hchan, pc uintptr, elem unsafe.Pointer, index int32) {
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i := sel.ncase
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if i >= sel.tcase {
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throw("selectsend: too many cases")
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}
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sel.ncase = i + 1
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cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
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cas.pc = pc
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cas.c = c
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cas.index = uint16(index)
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cas.kind = caseSend
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cas.elem = elem
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if debugSelect {
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print("selectsend s=", sel, " pc=", hex(cas.pc), " chan=", cas.c, " index=", cas.index, "\n")
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}
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}
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func selectrecv(sel *hselect, c *hchan, elem unsafe.Pointer, index int32) {
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// nil cases do not compete
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if c != nil {
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selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, nil, index)
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}
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return
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}
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func selectrecv2(sel *hselect, c *hchan, elem unsafe.Pointer, received *bool, index int32) {
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// nil cases do not compete
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if c != nil {
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selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, received, index)
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}
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return
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}
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func selectrecvImpl(sel *hselect, c *hchan, pc uintptr, elem unsafe.Pointer, received *bool, index int32) {
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i := sel.ncase
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if i >= sel.tcase {
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throw("selectrecv: too many cases")
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}
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sel.ncase = i + 1
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cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
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cas.pc = pc
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cas.c = c
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cas.index = uint16(index)
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cas.kind = caseRecv
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cas.elem = elem
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cas.receivedp = received
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if debugSelect {
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print("selectrecv s=", sel, " pc=", hex(cas.pc), " chan=", cas.c, " index=", cas.index, "\n")
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}
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}
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func selectdefault(sel *hselect, index int32) {
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selectdefaultImpl(sel, getcallerpc(unsafe.Pointer(&sel)), index)
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return
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}
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func selectdefaultImpl(sel *hselect, callerpc uintptr, index int32) {
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i := sel.ncase
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if i >= sel.tcase {
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throw("selectdefault: too many cases")
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}
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sel.ncase = i + 1
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cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
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cas.pc = callerpc
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cas.c = nil
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cas.index = uint16(index)
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cas.kind = caseDefault
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if debugSelect {
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print("selectdefault s=", sel, " pc=", hex(cas.pc), " index=", cas.index, "\n")
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}
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}
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func sellock(scases []scase, lockorder []uint16) {
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var c *hchan
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for _, o := range lockorder {
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c0 := scases[o].c
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if c0 != nil && c0 != c {
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c = c0
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lock(&c.lock)
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}
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}
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}
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func selunlock(scases []scase, lockorder []uint16) {
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// We must be very careful here to not touch sel after we have unlocked
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// the last lock, because sel can be freed right after the last unlock.
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// Consider the following situation.
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// First M calls runtime·park() in runtime·selectgo() passing the sel.
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// Once runtime·park() has unlocked the last lock, another M makes
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// the G that calls select runnable again and schedules it for execution.
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// When the G runs on another M, it locks all the locks and frees sel.
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// Now if the first M touches sel, it will access freed memory.
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n := len(scases)
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r := 0
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// skip the default case
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if n > 0 && scases[lockorder[0]].c == nil {
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r = 1
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}
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for i := n - 1; i >= r; i-- {
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c := scases[lockorder[i]].c
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if i > 0 && c == scases[lockorder[i-1]].c {
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continue // will unlock it on the next iteration
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}
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unlock(&c.lock)
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}
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}
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func selparkcommit(gp *g, _ unsafe.Pointer) bool {
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// This must not access gp's stack (see gopark). In
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// particular, it must not access the *hselect. That's okay,
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// because by the time this is called, gp.waiting has all
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// channels in lock order.
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var lastc *hchan
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for sg := gp.waiting; sg != nil; sg = sg.waitlink {
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if sg.c != lastc && lastc != nil {
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// As soon as we unlock the channel, fields in
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// any sudog with that channel may change,
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// including c and waitlink. Since multiple
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// sudogs may have the same channel, we unlock
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// only after we've passed the last instance
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// of a channel.
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unlock(&lastc.lock)
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}
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lastc = sg.c
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}
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if lastc != nil {
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unlock(&lastc.lock)
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}
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return true
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}
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func block() {
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gopark(nil, nil, "select (no cases)", traceEvGoStop, 1) // forever
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}
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// selectgo implements the select statement.
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//
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// *sel is on the current goroutine's stack (regardless of any
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// escaping in selectgo).
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//
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// selectgo does not return. Instead, it overwrites its return PC and
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// returns directly to the triggered select case. Because of this, it
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// cannot appear at the top of a split stack.
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func selectgo(sel *hselect) int32 {
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_, index := selectgoImpl(sel)
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return int32(index)
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}
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// selectgoImpl returns scase.pc and scase.so for the select
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// case which fired.
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func selectgoImpl(sel *hselect) (uintptr, uint16) {
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if debugSelect {
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print("select: sel=", sel, "\n")
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}
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scaseslice := slice{unsafe.Pointer(&sel.scase), int(sel.ncase), int(sel.ncase)}
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scases := *(*[]scase)(unsafe.Pointer(&scaseslice))
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var t0 int64
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if blockprofilerate > 0 {
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t0 = cputicks()
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for i := 0; i < int(sel.ncase); i++ {
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scases[i].releasetime = -1
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}
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}
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// The compiler rewrites selects that statically have
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// only 0 or 1 cases plus default into simpler constructs.
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// The only way we can end up with such small sel.ncase
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// values here is for a larger select in which most channels
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// have been nilled out. The general code handles those
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// cases correctly, and they are rare enough not to bother
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// optimizing (and needing to test).
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// generate permuted order
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pollslice := slice{unsafe.Pointer(sel.pollorder), int(sel.ncase), int(sel.ncase)}
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pollorder := *(*[]uint16)(unsafe.Pointer(&pollslice))
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for i := 1; i < int(sel.ncase); i++ {
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j := int(fastrand()) % (i + 1)
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pollorder[i] = pollorder[j]
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pollorder[j] = uint16(i)
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}
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// sort the cases by Hchan address to get the locking order.
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// simple heap sort, to guarantee n log n time and constant stack footprint.
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lockslice := slice{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
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lockorder := *(*[]uint16)(unsafe.Pointer(&lockslice))
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for i := 0; i < int(sel.ncase); i++ {
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j := i
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// Start with the pollorder to permute cases on the same channel.
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c := scases[pollorder[i]].c
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for j > 0 && scases[lockorder[(j-1)/2]].c.sortkey() < c.sortkey() {
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k := (j - 1) / 2
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lockorder[j] = lockorder[k]
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j = k
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}
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lockorder[j] = pollorder[i]
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}
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for i := int(sel.ncase) - 1; i >= 0; i-- {
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o := lockorder[i]
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c := scases[o].c
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lockorder[i] = lockorder[0]
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j := 0
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for {
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k := j*2 + 1
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if k >= i {
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break
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}
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if k+1 < i && scases[lockorder[k]].c.sortkey() < scases[lockorder[k+1]].c.sortkey() {
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k++
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}
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if c.sortkey() < scases[lockorder[k]].c.sortkey() {
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lockorder[j] = lockorder[k]
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j = k
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continue
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}
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break
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}
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lockorder[j] = o
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}
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/*
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for i := 0; i+1 < int(sel.ncase); i++ {
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if scases[lockorder[i]].c.sortkey() > scases[lockorder[i+1]].c.sortkey() {
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print("i=", i, " x=", lockorder[i], " y=", lockorder[i+1], "\n")
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throw("select: broken sort")
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}
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}
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*/
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// lock all the channels involved in the select
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sellock(scases, lockorder)
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var (
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gp *g
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done uint32
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sg *sudog
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c *hchan
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k *scase
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sglist *sudog
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sgnext *sudog
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qp unsafe.Pointer
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nextp **sudog
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)
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loop:
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// pass 1 - look for something already waiting
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var dfl *scase
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var cas *scase
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for i := 0; i < int(sel.ncase); i++ {
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cas = &scases[pollorder[i]]
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c = cas.c
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switch cas.kind {
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case caseRecv:
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sg = c.sendq.dequeue()
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if sg != nil {
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goto recv
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}
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if c.qcount > 0 {
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goto bufrecv
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}
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if c.closed != 0 {
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goto rclose
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}
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case caseSend:
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if raceenabled {
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racereadpc(unsafe.Pointer(c), cas.pc, chansendpc)
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}
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if c.closed != 0 {
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goto sclose
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}
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sg = c.recvq.dequeue()
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if sg != nil {
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goto send
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}
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if c.qcount < c.dataqsiz {
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goto bufsend
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}
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case caseDefault:
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dfl = cas
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}
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}
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if dfl != nil {
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selunlock(scases, lockorder)
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cas = dfl
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goto retc
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}
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// pass 2 - enqueue on all chans
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gp = getg()
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done = 0
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if gp.waiting != nil {
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throw("gp.waiting != nil")
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}
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nextp = &gp.waiting
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for _, casei := range lockorder {
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cas = &scases[casei]
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c = cas.c
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sg := acquireSudog()
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sg.g = gp
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// Note: selectdone is adjusted for stack copies in stack1.go:adjustsudogs
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sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done)))
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// No stack splits between assigning elem and enqueuing
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// sg on gp.waiting where copystack can find it.
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sg.elem = cas.elem
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sg.releasetime = 0
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if t0 != 0 {
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sg.releasetime = -1
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}
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sg.c = c
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// Construct waiting list in lock order.
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*nextp = sg
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nextp = &sg.waitlink
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switch cas.kind {
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case caseRecv:
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c.recvq.enqueue(sg)
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case caseSend:
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c.sendq.enqueue(sg)
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}
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}
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// wait for someone to wake us up
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gp.param = nil
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gopark(selparkcommit, nil, "select", traceEvGoBlockSelect, 2)
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// While we were asleep, some goroutine came along and completed
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// one of the cases in the select and woke us up (called ready).
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// As part of that process, the goroutine did a cas on done above
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// (aka *sg.selectdone for all queued sg) to win the right to
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// complete the select. Now done = 1.
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//
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// If we copy (grow) our own stack, we will update the
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// selectdone pointers inside the gp.waiting sudog list to point
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// at the new stack. Another goroutine attempting to
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// complete one of our (still linked in) select cases might
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// see the new selectdone pointer (pointing at the new stack)
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// before the new stack has real data; if the new stack has done = 0
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// (before the old values are copied over), the goroutine might
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// do a cas via sg.selectdone and incorrectly believe that it has
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// won the right to complete the select, executing a second
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// communication and attempting to wake us (call ready) again.
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//
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// Then things break.
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//
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// The best break is that the goroutine doing ready sees the
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// _Gcopystack status and throws, as in #17007.
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// A worse break would be for us to continue on, start running real code,
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// block in a semaphore acquisition (sema.go), and have the other
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// goroutine wake us up without having really acquired the semaphore.
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// That would result in the goroutine spuriously running and then
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// queue up another spurious wakeup when the semaphore really is ready.
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// In general the situation can cascade until something notices the
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// problem and causes a crash.
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//
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// A stack shrink does not have this problem, because it locks
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// all the channels that are involved first, blocking out the
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// possibility of a cas on selectdone.
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//
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// A stack growth before gopark above does not have this
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// problem, because we hold those channel locks (released by
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// selparkcommit).
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//
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// A stack growth after sellock below does not have this
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// problem, because again we hold those channel locks.
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//
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// The only problem is a stack growth during sellock.
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// To keep that from happening, run sellock on the system stack.
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//
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// It might be that we could avoid this if copystack copied the
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// stack before calling adjustsudogs. In that case,
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// syncadjustsudogs would need to recopy the tiny part that
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// it copies today, resulting in a little bit of extra copying.
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//
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// An even better fix, not for the week before a release candidate,
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// would be to put space in every sudog and make selectdone
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// point at (say) the space in the first sudog.
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systemstack(func() {
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sellock(scases, lockorder)
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})
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sg = (*sudog)(gp.param)
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gp.param = nil
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// pass 3 - dequeue from unsuccessful chans
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// otherwise they stack up on quiet channels
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// record the successful case, if any.
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// We singly-linked up the SudoGs in lock order.
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cas = nil
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sglist = gp.waiting
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// Clear all elem before unlinking from gp.waiting.
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for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink {
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sg1.selectdone = nil
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sg1.elem = nil
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sg1.c = nil
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}
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gp.waiting = nil
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for _, casei := range lockorder {
|
|
k = &scases[casei]
|
|
if sglist.releasetime > 0 {
|
|
k.releasetime = sglist.releasetime
|
|
}
|
|
if sg == sglist {
|
|
// sg has already been dequeued by the G that woke us up.
|
|
cas = k
|
|
} else {
|
|
c = k.c
|
|
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 {
|
|
// We can wake up with gp.param == nil (so cas == nil)
|
|
// when a channel involved in the select has been closed.
|
|
// It is easiest to loop and re-run the operation;
|
|
// we'll see that it's now closed.
|
|
// Maybe some day we can signal the close explicitly,
|
|
// but we'd have to distinguish close-on-reader from close-on-writer.
|
|
// It's easiest not to duplicate the code and just recheck above.
|
|
// We know that something closed, and things never un-close,
|
|
// so we won't block again.
|
|
goto loop
|
|
}
|
|
|
|
c = cas.c
|
|
|
|
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)
|
|
}
|
|
}
|
|
if msanenabled {
|
|
if cas.kind == caseRecv && cas.elem != nil {
|
|
msanwrite(cas.elem, c.elemtype.size)
|
|
} else if cas.kind == caseSend {
|
|
msanread(cas.elem, c.elemtype.size)
|
|
}
|
|
}
|
|
|
|
selunlock(scases, lockorder)
|
|
goto retc
|
|
|
|
bufrecv:
|
|
// 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 msanenabled && cas.elem != nil {
|
|
msanwrite(cas.elem, c.elemtype.size)
|
|
}
|
|
if cas.receivedp != nil {
|
|
*cas.receivedp = true
|
|
}
|
|
qp = chanbuf(c, c.recvx)
|
|
if cas.elem != nil {
|
|
typedmemmove(c.elemtype, cas.elem, qp)
|
|
}
|
|
typedmemclr(c.elemtype, qp)
|
|
c.recvx++
|
|
if c.recvx == c.dataqsiz {
|
|
c.recvx = 0
|
|
}
|
|
c.qcount--
|
|
selunlock(scases, lockorder)
|
|
goto retc
|
|
|
|
bufsend:
|
|
// can send to buffer
|
|
if raceenabled {
|
|
raceacquire(chanbuf(c, c.sendx))
|
|
racerelease(chanbuf(c, c.sendx))
|
|
raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
|
|
}
|
|
if msanenabled {
|
|
msanread(cas.elem, c.elemtype.size)
|
|
}
|
|
typedmemmove(c.elemtype, chanbuf(c, c.sendx), cas.elem)
|
|
c.sendx++
|
|
if c.sendx == c.dataqsiz {
|
|
c.sendx = 0
|
|
}
|
|
c.qcount++
|
|
selunlock(scases, lockorder)
|
|
goto retc
|
|
|
|
recv:
|
|
// can receive from sleeping sender (sg)
|
|
recv(c, sg, cas.elem, func() { selunlock(scases, lockorder) })
|
|
if debugSelect {
|
|
print("syncrecv: sel=", sel, " c=", c, "\n")
|
|
}
|
|
if cas.receivedp != nil {
|
|
*cas.receivedp = true
|
|
}
|
|
goto retc
|
|
|
|
rclose:
|
|
// read at end of closed channel
|
|
selunlock(scases, lockorder)
|
|
if cas.receivedp != nil {
|
|
*cas.receivedp = false
|
|
}
|
|
if cas.elem != nil {
|
|
typedmemclr(c.elemtype, cas.elem)
|
|
}
|
|
if raceenabled {
|
|
raceacquire(unsafe.Pointer(c))
|
|
}
|
|
goto retc
|
|
|
|
send:
|
|
// can send to a sleeping receiver (sg)
|
|
if raceenabled {
|
|
raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
|
|
}
|
|
if msanenabled {
|
|
msanread(cas.elem, c.elemtype.size)
|
|
}
|
|
send(c, sg, cas.elem, func() { selunlock(scases, lockorder) })
|
|
if debugSelect {
|
|
print("syncsend: sel=", sel, " c=", c, "\n")
|
|
}
|
|
goto retc
|
|
|
|
retc:
|
|
if cas.releasetime > 0 {
|
|
blockevent(cas.releasetime-t0, 2)
|
|
}
|
|
return cas.pc, cas.index
|
|
|
|
sclose:
|
|
// send on closed channel
|
|
selunlock(scases, lockorder)
|
|
panic(plainError("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
|
|
)
|
|
|
|
//go:linkname reflect_rselect reflect.rselect
|
|
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 := (*hselect)(mallocgc(size, nil, true))
|
|
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(sgp *sudog) {
|
|
x := sgp.prev
|
|
y := sgp.next
|
|
if x != nil {
|
|
if y != nil {
|
|
// middle of queue
|
|
x.next = y
|
|
y.prev = x
|
|
sgp.next = nil
|
|
sgp.prev = nil
|
|
return
|
|
}
|
|
// end of queue
|
|
x.next = nil
|
|
q.last = x
|
|
sgp.prev = nil
|
|
return
|
|
}
|
|
if y != nil {
|
|
// start of queue
|
|
y.prev = nil
|
|
q.first = y
|
|
sgp.next = nil
|
|
return
|
|
}
|
|
|
|
// x==y==nil. Either sgp is the only element in the queue,
|
|
// or it has already been removed. Use q.first to disambiguate.
|
|
if q.first == sgp {
|
|
q.first = nil
|
|
q.last = nil
|
|
}
|
|
}
|