This libgo patch adds a success field to the sudog structure used to
manage select statements. This is a step toward enabling some
compiler changes as part of upgrading to the Go 1.16beta1 release.
Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu. Committed
to mainline.
Ian
3b2d8145a4c349058d76ce299ea7eea605572004
diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index a7df8433403..bb537f152b9 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-d0e56e82bb298268ec0f306fef99a715c892d4a7
+eca96e39cb895805b617e0e1f184f893ed3e46bb
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.
diff --git a/libgo/go/runtime/chan.go b/libgo/go/runtime/chan.go
index 8e104f14140..1b20aff6ea3 100644
--- a/libgo/go/runtime/chan.go
+++ b/libgo/go/runtime/chan.go
@@ -285,18 +285,19 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool,
callerpc uintptr) bool {
}
gp.waiting = nil
gp.activeStackChans = false
- if gp.param == nil {
- if c.closed == 0 {
- throw("chansend: spurious wakeup")
- }
- panic(plainError("send on closed channel"))
- }
+ closed := !mysg.success
gp.param = nil
if mysg.releasetime > 0 {
blockevent(mysg.releasetime-t0, 2)
}
mysg.c = nil
releaseSudog(mysg)
+ if closed {
+ if c.closed == 0 {
+ throw("chansend: spurious wakeup")
+ }
+ panic(plainError("send on closed channel"))
+ }
return true
}
@@ -333,6 +334,7 @@ func send(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf
func(), skip int) {
gp := sg.g
unlockf()
gp.param = unsafe.Pointer(sg)
+ sg.success = true
if sg.releasetime != 0 {
sg.releasetime = cputicks()
}
@@ -406,7 +408,8 @@ func closechan(c *hchan) {
sg.releasetime = cputicks()
}
gp := sg.g
- gp.param = nil
+ gp.param = unsafe.Pointer(sg)
+ sg.success = false
if raceenabled {
raceacquireg(gp, c.raceaddr())
}
@@ -424,7 +427,8 @@ func closechan(c *hchan) {
sg.releasetime = cputicks()
}
gp := sg.g
- gp.param = nil
+ gp.param = unsafe.Pointer(sg)
+ sg.success = false
if raceenabled {
raceacquireg(gp, c.raceaddr())
}
@@ -607,11 +611,11 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool)
(selected, received bool)
if mysg.releasetime > 0 {
blockevent(mysg.releasetime-t0, 2)
}
- closed := gp.param == nil
+ success := mysg.success
gp.param = nil
mysg.c = nil
releaseSudog(mysg)
- return true, !closed
+ return true, success
}
// recv processes a receive operation on a full channel c.
@@ -664,6 +668,7 @@ func recv(c *hchan, sg *sudog, ep unsafe.Pointer, unlockf
func(), skip int) {
gp := sg.g
unlockf()
gp.param = unsafe.Pointer(sg)
+ sg.success = true
if sg.releasetime != 0 {
sg.releasetime = cputicks()
}
diff --git a/libgo/go/runtime/runtime2.go b/libgo/go/runtime/runtime2.go
index bf3fbac14c8..f30d1bcde6e 100644
--- a/libgo/go/runtime/runtime2.go
+++ b/libgo/go/runtime/runtime2.go
@@ -354,6 +354,12 @@ type sudog struct {
// g.selectDone must be CAS'd to win the wake-up race.
isSelect bool
+ // success indicates whether communication over channel c
+ // succeeded. It is true if the goroutine was awoken because a
+ // value was delivered over channel c, and false if awoken
+ // because c was closed.
+ success bool
+
parent *sudog // semaRoot binary tree
waitlink *sudog // g.waiting list or semaRoot
waittail *sudog // semaRoot
diff --git a/libgo/go/runtime/select.go b/libgo/go/runtime/select.go
index d5087fbc045..c31aa344b55 100644
--- a/libgo/go/runtime/select.go
+++ b/libgo/go/runtime/select.go
@@ -235,10 +235,10 @@ func selectgo(cas0 *scase, order0 *uint16, ncases int)
(int, bool) {
nextp **sudog
)
-loop:
// 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 {
@@ -335,6 +335,7 @@ loop:
// 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 {
@@ -350,6 +351,7 @@ loop:
// 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
}
@@ -368,16 +370,7 @@ loop:
}
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
+ throw("selectgo: bad wakeup")
}
c = cas.c
@@ -387,7 +380,9 @@ loop:
}
if cas.kind == caseRecv {
- recvOK = true
+ recvOK = caseSuccess
+ } else if cas.kind == caseSend && !caseSuccess {
+ goto sclose
}
selunlock(scases, lockorder)
