From ccd992355df7192993c666236047820244914598 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Tue, 16 Apr 2024 21:19:13 +0200
Subject: Adding upstream version 1.21.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 src/runtime/select.go | 632 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 632 insertions(+)
 create mode 100644 src/runtime/select.go

(limited to 'src/runtime/select.go')

diff --git a/src/runtime/select.go b/src/runtime/select.go
new file mode 100644
index 0000000..34c0637
--- /dev/null
+++ b/src/runtime/select.go
@@ -0,0 +1,632 @@
+// 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 (
+	"internal/abi"
+	"unsafe"
+)
+
+const debugSelect = false
+
+// Select case descriptor.
+// Known to compiler.
+// Changes here must also be made in src/cmd/compile/internal/walk/select.go's scasetype.
+type scase struct {
+	c    *hchan         // chan
+	elem unsafe.Pointer // data element
+}
+
+var (
+	chansendpc = abi.FuncPCABIInternal(chansend)
+	chanrecvpc = abi.FuncPCABIInternal(chanrecv)
+)
+
+func selectsetpc(pc *uintptr) {
+	*pc = getcallerpc()
+}
+
+func sellock(scases []scase, lockorder []uint16) {
+	var c *hchan
+	for _, o := range lockorder {
+		c0 := scases[o].c
+		if c0 != c {
+			c = c0
+			lock(&c.lock)
+		}
+	}
+}
+
+func selunlock(scases []scase, lockorder []uint16) {
+	// 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.
+	for i := len(lockorder) - 1; i >= 0; i-- {
+		c := scases[lockorder[i]].c
+		if i > 0 && c == scases[lockorder[i-1]].c {
+			continue // will unlock it on the next iteration
+		}
+		unlock(&c.lock)
+	}
+}
+
+func selparkcommit(gp *g, _ unsafe.Pointer) bool {
+	// There are unlocked sudogs that point into gp's stack. Stack
+	// copying must lock the channels of those sudogs.
+	// Set activeStackChans here instead of before we try parking
+	// because we could self-deadlock in stack growth on a
+	// channel lock.
+	gp.activeStackChans = true
+	// Mark that it's safe for stack shrinking to occur now,
+	// because any thread acquiring this G's stack for shrinking
+	// is guaranteed to observe activeStackChans after this store.
+	gp.parkingOnChan.Store(false)
+	// Make sure we unlock after setting activeStackChans and
+	// unsetting parkingOnChan. The moment we unlock any of the
+	// channel locks we risk gp getting readied by a channel operation
+	// and so gp could continue running before everything before the
+	// unlock is visible (even to gp itself).
+
+	// This must not access gp's stack (see gopark). In
+	// particular, it must not access the *hselect. That's okay,
+	// because by the time this is called, gp.waiting has all
+	// channels in lock order.
+	var lastc *hchan
+	for sg := gp.waiting; sg != nil; sg = sg.waitlink {
+		if sg.c != lastc && lastc != nil {
+			// As soon as we unlock the channel, fields in
+			// any sudog with that channel may change,
+			// including c and waitlink. Since multiple
+			// sudogs may have the same channel, we unlock
+			// only after we've passed the last instance
+			// of a channel.
+			unlock(&lastc.lock)
+		}
+		lastc = sg.c
+	}
+	if lastc != nil {
+		unlock(&lastc.lock)
+	}
+	return true
+}
+
+func block() {
+	gopark(nil, nil, waitReasonSelectNoCases, traceBlockForever, 1) // forever
+}
+
+// selectgo implements the select statement.
+//
+// cas0 points to an array of type [ncases]scase, and order0 points to
+// an array of type [2*ncases]uint16 where ncases must be <= 65536.
+// Both reside on the goroutine's stack (regardless of any escaping in
+// selectgo).
+//
+// For race detector builds, pc0 points to an array of type
+// [ncases]uintptr (also on the stack); for other builds, it's set to
+// nil.
+//
+// selectgo returns the index of the chosen scase, which matches the
+// ordinal position of its respective select{recv,send,default} call.
+// Also, if the chosen scase was a receive operation, it reports whether
+// a value was received.
+func selectgo(cas0 *scase, order0 *uint16, pc0 *uintptr, nsends, nrecvs int, block bool) (int, bool) {
+	if debugSelect {
+		print("select: cas0=", cas0, "\n")
+	}
+
+	// NOTE: In order to maintain a lean stack size, the number of scases
+	// is capped at 65536.
+	cas1 := (*[1 << 16]scase)(unsafe.Pointer(cas0))
+	order1 := (*[1 << 17]uint16)(unsafe.Pointer(order0))
+
+	ncases := nsends + nrecvs
+	scases := cas1[:ncases:ncases]
+	pollorder := order1[:ncases:ncases]
+	lockorder := order1[ncases:][:ncases:ncases]
+	// NOTE: pollorder/lockorder's underlying array was not zero-initialized by compiler.
+
+	// Even when raceenabled is true, there might be select
+	// statements in packages compiled without -race (e.g.,
+	// ensureSigM in runtime/signal_unix.go).
+	var pcs []uintptr
+	if raceenabled && pc0 != nil {
+		pc1 := (*[1 << 16]uintptr)(unsafe.Pointer(pc0))
+		pcs = pc1[:ncases:ncases]
+	}
+	casePC := func(casi int) uintptr {
+		if pcs == nil {
+			return 0
+		}
+		return pcs[casi]
+	}
+
+	var t0 int64
+	if blockprofilerate > 0 {
+		t0 = cputicks()
+	}
+
+	// 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
+	norder := 0
+	for i := range scases {
+		cas := &scases[i]
+
+		// Omit cases without channels from the poll and lock orders.
+		if cas.c == nil {
+			cas.elem = nil // allow GC
+			continue
+		}
+
+		j := fastrandn(uint32(norder + 1))
+		pollorder[norder] = pollorder[j]
+		pollorder[j] = uint16(i)
+		norder++
+	}
+	pollorder = pollorder[:norder]
+	lockorder = lockorder[:norder]
+
+	// sort the cases by Hchan address to get the locking order.
+	// simple heap sort, to guarantee n log n time and constant stack footprint.
+	for i := range lockorder {
+		j := i
+		// Start with the pollorder to permute cases on the same channel.
+		c := scases[pollorder[i]].c
+		for j > 0 && scases[lockorder[(j-1)/2]].c.sortkey() < c.sortkey() {
+			k := (j - 1) / 2
+			lockorder[j] = lockorder[k]
+			j = k
+		}
+		lockorder[j] = pollorder[i]
+	}
+	for i := len(lockorder) - 1; i >= 0; i-- {
+		o := lockorder[i]
+		c := scases[o].c
+		lockorder[i] = lockorder[0]
+		j := 0
+		for {
+			k := j*2 + 1
+			if k >= i {
+				break
+			}
+			if k+1 < i && scases[lockorder[k]].c.sortkey() < scases[lockorder[k+1]].c.sortkey() {
+				k++
+			}
+			if c.sortkey() < scases[lockorder[k]].c.sortkey() {
+				lockorder[j] = lockorder[k]
+				j = k
+				continue
+			}
+			break
+		}
+		lockorder[j] = o
+	}
+
+	if debugSelect {
+		for i := 0; i+1 < len(lockorder); i++ {
+			if scases[lockorder[i]].c.sortkey() > scases[lockorder[i+1]].c.sortkey() {
+				print("i=", i, " x=", lockorder[i], " y=", lockorder[i+1], "\n")
+				throw("select: broken sort")
+			}
+		}
+	}
+
+	// lock all the channels involved in the select
+	sellock(scases, lockorder)
+
+	var (
+		gp     *g
+		sg     *sudog
+		c      *hchan
+		k      *scase
+		sglist *sudog
+		sgnext *sudog
+		qp     unsafe.Pointer
+		nextp  **sudog
+	)
+
+	// pass 1 - look for something already waiting
+	var casi int
+	var cas *scase
+	var caseSuccess bool
+	var caseReleaseTime int64 = -1
+	var recvOK bool
+	for _, casei := range pollorder {
+		casi = int(casei)
+		cas = &scases[casi]
+		c = cas.c
+
+		if casi >= nsends {
+			sg = c.sendq.dequeue()
+			if sg != nil {
+				goto recv
+			}
+			if c.qcount > 0 {
+				goto bufrecv
+			}
+			if c.closed != 0 {
+				goto rclose
+			}
+		} else {
+			if raceenabled {
+				racereadpc(c.raceaddr(), casePC(casi), chansendpc)
+			}
+			if c.closed != 0 {
+				goto sclose
+			}
+			sg = c.recvq.dequeue()
+			if sg != nil {
+				goto send
+			}
+			if c.qcount < c.dataqsiz {
+				goto bufsend
+			}
+		}
+	}
+
+	if !block {
+		selunlock(scases, lockorder)
+		casi = -1
+		goto retc
+	}
+
+	// pass 2 - enqueue on all chans
+	gp = getg()
+	if gp.waiting != nil {
+		throw("gp.waiting != nil")
+	}
+	nextp = &gp.waiting
+	for _, casei := range lockorder {
+		casi = int(casei)
+		cas = &scases[casi]
+		c = cas.c
+		sg := acquireSudog()
+		sg.g = gp
+		sg.isSelect = true
+		// No stack splits between assigning elem and enqueuing
+		// sg on gp.waiting where copystack can find it.
+		sg.elem = cas.elem
+		sg.releasetime = 0
+		if t0 != 0 {
+			sg.releasetime = -1
+		}
+		sg.c = c
+		// Construct waiting list in lock order.
+		*nextp = sg
+		nextp = &sg.waitlink
+
+		if casi < nsends {
+			c.sendq.enqueue(sg)
+		} else {
+			c.recvq.enqueue(sg)
+		}
+	}
+
+	// wait for someone to wake us up
+	gp.param = nil
+	// Signal to anyone trying to shrink our stack that we're about
+	// to park on a channel. The window between when this G's status
+	// changes and when we set gp.activeStackChans is not safe for
+	// stack shrinking.
+	gp.parkingOnChan.Store(true)
+	gopark(selparkcommit, nil, waitReasonSelect, traceBlockSelect, 1)
+	gp.activeStackChans = false
+
+	sellock(scases, lockorder)
+
+	gp.selectDone.Store(0)
+	sg = (*sudog)(gp.param)
+	gp.param = nil
+
+	// pass 3 - dequeue from unsuccessful chans
+	// otherwise they stack up on quiet channels
+	// record the successful case, if any.
+	// We singly-linked up the SudoGs in lock order.
+	casi = -1
+	cas = nil
+	caseSuccess = false
+	sglist = gp.waiting
+	// Clear all elem before unlinking from gp.waiting.
+	for sg1 := gp.waiting; sg1 != nil; sg1 = sg1.waitlink {
+		sg1.isSelect = false
+		sg1.elem = nil
+		sg1.c = nil
+	}
+	gp.waiting = nil
+
+	for _, casei := range lockorder {
+		k = &scases[casei]
+		if sg == sglist {
+			// sg has already been dequeued by the G that woke us up.
+			casi = int(casei)
+			cas = k
+			caseSuccess = sglist.success
+			if sglist.releasetime > 0 {
+				caseReleaseTime = sglist.releasetime
+			}
+		} else {
+			c = k.c
+			if int(casei) < nsends {
+				c.sendq.dequeueSudoG(sglist)
+			} else {
+				c.recvq.dequeueSudoG(sglist)
+			}
+		}
+		sgnext = sglist.waitlink
+		sglist.waitlink = nil
+		releaseSudog(sglist)
+		sglist = sgnext
+	}
+
+	if cas == nil {
+		throw("selectgo: bad wakeup")
+	}
+
+	c = cas.c
+
+	if debugSelect {
+		print("wait-return: cas0=", cas0, " c=", c, " cas=", cas, " send=", casi < nsends, "\n")
+	}
+
+	if casi < nsends {
+		if !caseSuccess {
+			goto sclose
+		}
+	} else {
+		recvOK = caseSuccess
+	}
+
+	if raceenabled {
+		if casi < nsends {
+			raceReadObjectPC(c.elemtype, cas.elem, casePC(casi), chansendpc)
+		} else if cas.elem != nil {
+			raceWriteObjectPC(c.elemtype, cas.elem, casePC(casi), chanrecvpc)
+		}
+	}
+	if msanenabled {
+		if casi < nsends {
+			msanread(cas.elem, c.elemtype.Size_)
+		} else if cas.elem != nil {
+			msanwrite(cas.elem, c.elemtype.Size_)
+		}
+	}
+	if asanenabled {
+		if casi < nsends {
+			asanread(cas.elem, c.elemtype.Size_)
+		} else if cas.elem != nil {
+			asanwrite(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, casePC(casi), chanrecvpc)
+		}
+		racenotify(c, c.recvx, nil)
+	}
+	if msanenabled && cas.elem != nil {
+		msanwrite(cas.elem, c.elemtype.Size_)
+	}
+	if asanenabled && cas.elem != nil {
+		asanwrite(cas.elem, c.elemtype.Size_)
+	}
+	recvOK = 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 {
+		racenotify(c, c.sendx, nil)
+		raceReadObjectPC(c.elemtype, cas.elem, casePC(casi), chansendpc)
+	}
+	if msanenabled {
+		msanread(cas.elem, c.elemtype.Size_)
+	}
+	if asanenabled {
+		asanread(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) }, 2)
+	if debugSelect {
+		print("syncrecv: cas0=", cas0, " c=", c, "\n")
+	}
+	recvOK = true
+	goto retc
+
+rclose:
+	// read at end of closed channel
+	selunlock(scases, lockorder)
+	recvOK = false
+	if cas.elem != nil {
+		typedmemclr(c.elemtype, cas.elem)
+	}
+	if raceenabled {
+		raceacquire(c.raceaddr())
+	}
+	goto retc
+
+send:
+	// can send to a sleeping receiver (sg)
+	if raceenabled {
+		raceReadObjectPC(c.elemtype, cas.elem, casePC(casi), chansendpc)
+	}
+	if msanenabled {
+		msanread(cas.elem, c.elemtype.Size_)
+	}
+	if asanenabled {
+		asanread(cas.elem, c.elemtype.Size_)
+	}
+	send(c, sg, cas.elem, func() { selunlock(scases, lockorder) }, 2)
+	if debugSelect {
+		print("syncsend: cas0=", cas0, " c=", c, "\n")
+	}
+	goto retc
+
+retc:
+	if caseReleaseTime > 0 {
+		blockevent(caseReleaseTime-t0, 1)
+	}
+	return casi, recvOK
+
+sclose:
+	// send on closed channel
+	selunlock(scases, lockorder)
+	panic(plainError("send on closed channel"))
+}
+
+func (c *hchan) sortkey() uintptr {
+	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) (int, bool) {
+	if len(cases) == 0 {
+		block()
+	}
+	sel := make([]scase, len(cases))
+	orig := make([]int, len(cases))
+	nsends, nrecvs := 0, 0
+	dflt := -1
+	for i, rc := range cases {
+		var j int
+		switch rc.dir {
+		case selectDefault:
+			dflt = i
+			continue
+		case selectSend:
+			j = nsends
+			nsends++
+		case selectRecv:
+			nrecvs++
+			j = len(cases) - nrecvs
+		}
+
+		sel[j] = scase{c: rc.ch, elem: rc.val}
+		orig[j] = i
+	}
+
+	// Only a default case.
+	if nsends+nrecvs == 0 {
+		return dflt, false
+	}
+
+	// Compact sel and orig if necessary.
+	if nsends+nrecvs < len(cases) {
+		copy(sel[nsends:], sel[len(cases)-nrecvs:])
+		copy(orig[nsends:], orig[len(cases)-nrecvs:])
+	}
+
+	order := make([]uint16, 2*(nsends+nrecvs))
+	var pc0 *uintptr
+	if raceenabled {
+		pcs := make([]uintptr, nsends+nrecvs)
+		for i := range pcs {
+			selectsetpc(&pcs[i])
+		}
+		pc0 = &pcs[0]
+	}
+
+	chosen, recvOK := selectgo(&sel[0], &order[0], pc0, nsends, nrecvs, dflt == -1)
+
+	// Translate chosen back to caller's ordering.
+	if chosen < 0 {
+		chosen = dflt
+	} else {
+		chosen = orig[chosen]
+	}
+	return chosen, recvOK
+}
+
+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
+	}
+}
-- 
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