mirror of git://gcc.gnu.org/git/gcc.git
652 lines
15 KiB
Go
652 lines
15 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 "unsafe"
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const (
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debugSelect = false
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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(_select{}) +
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(size-1)*unsafe.Sizeof(_select{}.scase[0]) +
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size*unsafe.Sizeof(*_select{}.lockorder) +
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size*unsafe.Sizeof(*_select{}.pollorder)
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return round(selsize, _Int64Align)
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}
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func newselect(sel *_select, 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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gothrow("bad select size")
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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 = (**hchan)(add(unsafe.Pointer(&sel.scase), uintptr(size)*unsafe.Sizeof(_select{}.scase[0])))
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sel.pollorder = (*uint16)(add(unsafe.Pointer(sel.lockorder), uintptr(size)*unsafe.Sizeof(*_select{}.lockorder)))
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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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//go:nosplit
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func selectsend(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
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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, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
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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 *_select, c *hchan, pc uintptr, elem unsafe.Pointer, so uintptr) {
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i := sel.ncase
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if i >= sel.tcase {
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gothrow("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._chan = c
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cas.so = uint16(so)
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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._chan, " so=", cas.so, "\n")
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}
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}
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//go:nosplit
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func selectrecv(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
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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, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
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}
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return
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}
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//go:nosplit
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func selectrecv2(sel *_select, c *hchan, elem unsafe.Pointer, received *bool) (selected bool) {
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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, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
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}
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return
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}
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func selectrecvImpl(sel *_select, c *hchan, pc uintptr, elem unsafe.Pointer, received *bool, so uintptr) {
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i := sel.ncase
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if i >= sel.tcase {
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gothrow("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._chan = c
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cas.so = uint16(so)
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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._chan, " so=", cas.so, "\n")
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}
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}
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//go:nosplit
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func selectdefault(sel *_select) (selected bool) {
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selectdefaultImpl(sel, getcallerpc(unsafe.Pointer(&sel)), uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
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return
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}
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func selectdefaultImpl(sel *_select, callerpc uintptr, so uintptr) {
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i := sel.ncase
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if i >= sel.tcase {
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gothrow("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._chan = nil
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cas.so = uint16(so)
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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), " so=", cas.so, "\n")
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}
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}
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func sellock(sel *_select) {
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lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
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lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
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var c *hchan
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for _, c0 := range lockorder {
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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(sel *_select) {
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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 := int(sel.ncase)
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r := 0
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lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), n, n}
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lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
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// skip the default case
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if n > 0 && lockorder[0] == 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 := lockorder[i]
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if i > 0 && c == lockorder[i-1] {
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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, sel *_select) bool {
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selunlock(sel)
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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)") // forever
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}
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// overwrites return pc on stack to signal which case of the select
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// to run, so cannot appear at the top of a split stack.
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//go:nosplit
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func selectgo(sel *_select) {
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pc, offset := selectgoImpl(sel)
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*(*bool)(add(unsafe.Pointer(&sel), uintptr(offset))) = true
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setcallerpc(unsafe.Pointer(&sel), pc)
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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 *_select) (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 := sliceStruct{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 := sliceStruct{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 := 0; i < int(sel.ncase); i++ {
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pollorder[i] = uint16(i)
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}
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for i := 1; i < int(sel.ncase); i++ {
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o := pollorder[i]
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j := int(fastrand1()) % (i + 1)
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pollorder[i] = pollorder[j]
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pollorder[j] = o
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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 := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
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lockorder := *(*[]*hchan)(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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c := scases[j]._chan
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for j > 0 && lockorder[(j-1)/2].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] = c
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}
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for i := int(sel.ncase) - 1; i >= 0; i-- {
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c := lockorder[i]
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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 && lockorder[k].sortkey() < lockorder[k+1].sortkey() {
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k++
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}
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if c.sortkey() < lockorder[k].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] = c
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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 lockorder[i].sortkey() > lockorder[i+1].sortkey() {
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print("i=", i, " x=", lockorder[i], " y=", lockorder[i+1], "\n")
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gothrow("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(sel)
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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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)
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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._chan
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switch cas.kind {
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case _CaseRecv:
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if c.dataqsiz > 0 {
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if c.qcount > 0 {
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goto asyncrecv
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}
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} else {
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sg = c.sendq.dequeue()
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if sg != nil {
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goto syncrecv
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}
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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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if c.dataqsiz > 0 {
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if c.qcount < c.dataqsiz {
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goto asyncsend
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}
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} else {
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sg = c.recvq.dequeue()
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if sg != nil {
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goto syncsend
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}
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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(sel)
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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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for i := 0; i < int(sel.ncase); i++ {
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cas = &scases[pollorder[i]]
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c = cas._chan
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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 stack.c:adjustsudogs
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sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done)))
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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.waitlink = gp.waiting
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gp.waiting = sg
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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(unsafe.Pointer(funcPC(selparkcommit)), unsafe.Pointer(sel), "select")
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// someone woke us up
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sellock(sel)
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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 case order, so when
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// iterating through the linked list they are in reverse order.
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cas = nil
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sglist = gp.waiting
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// Clear all selectdone and elem before unlinking from gp.waiting.
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// They must be cleared before being put back into the sudog cache.
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// Clear before unlinking, because if a stack copy happens after the unlink,
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// they will not be updated, they will be left pointing to the old stack,
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// which creates dangling pointers, which may be detected by the
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// garbage collector.
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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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}
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gp.waiting = nil
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for i := int(sel.ncase) - 1; i >= 0; i-- {
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k = &scases[pollorder[i]]
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if sglist.releasetime > 0 {
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k.releasetime = sglist.releasetime
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}
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if sg == sglist {
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cas = k
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} else {
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c = k._chan
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if k.kind == _CaseSend {
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c.sendq.dequeueSudoG(sglist)
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} else {
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c.recvq.dequeueSudoG(sglist)
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}
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}
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sgnext = sglist.waitlink
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sglist.waitlink = nil
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releaseSudog(sglist)
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sglist = sgnext
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}
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if cas == nil {
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goto loop
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}
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c = cas._chan
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if c.dataqsiz > 0 {
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gothrow("selectgo: shouldn't happen")
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}
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if debugSelect {
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print("wait-return: sel=", sel, " c=", c, " cas=", cas, " kind=", cas.kind, "\n")
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}
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if cas.kind == _CaseRecv {
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if cas.receivedp != nil {
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*cas.receivedp = true
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}
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}
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if raceenabled {
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if cas.kind == _CaseRecv && cas.elem != nil {
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raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
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} else if cas.kind == _CaseSend {
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raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
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}
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}
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selunlock(sel)
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goto retc
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asyncrecv:
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// can receive from buffer
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if raceenabled {
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if cas.elem != nil {
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raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
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}
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raceacquire(chanbuf(c, c.recvx))
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racerelease(chanbuf(c, c.recvx))
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}
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if cas.receivedp != nil {
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*cas.receivedp = true
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}
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if cas.elem != nil {
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memmove(cas.elem, chanbuf(c, c.recvx), uintptr(c.elemsize))
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}
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memclr(chanbuf(c, c.recvx), uintptr(c.elemsize))
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c.recvx++
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if c.recvx == c.dataqsiz {
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c.recvx = 0
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}
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c.qcount--
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sg = c.sendq.dequeue()
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if sg != nil {
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gp = sg.g
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selunlock(sel)
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if sg.releasetime != 0 {
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sg.releasetime = cputicks()
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}
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goready(gp)
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} else {
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selunlock(sel)
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}
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goto retc
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asyncsend:
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// can send to buffer
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if raceenabled {
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raceacquire(chanbuf(c, c.sendx))
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racerelease(chanbuf(c, c.sendx))
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raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
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}
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memmove(chanbuf(c, c.sendx), cas.elem, uintptr(c.elemsize))
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c.sendx++
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if c.sendx == c.dataqsiz {
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c.sendx = 0
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}
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c.qcount++
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sg = c.recvq.dequeue()
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if sg != nil {
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gp = sg.g
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selunlock(sel)
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if sg.releasetime != 0 {
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sg.releasetime = cputicks()
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}
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goready(gp)
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} else {
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selunlock(sel)
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}
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goto retc
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syncrecv:
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// can receive from sleeping sender (sg)
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if raceenabled {
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if cas.elem != nil {
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raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
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}
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racesync(c, sg)
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}
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selunlock(sel)
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if debugSelect {
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print("syncrecv: sel=", sel, " c=", c, "\n")
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}
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if cas.receivedp != nil {
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*cas.receivedp = true
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}
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if cas.elem != nil {
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memmove(cas.elem, sg.elem, uintptr(c.elemsize))
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}
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sg.elem = nil
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gp = sg.g
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gp.param = unsafe.Pointer(sg)
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if sg.releasetime != 0 {
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sg.releasetime = cputicks()
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}
|
|
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
|
|
}
|
|
}
|