public inbox for gcc-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc r11-6308] runtime: add "success" field to sudog
@ 2020-12-22 20:13 Ian Lance Taylor
0 siblings, 0 replies; only message in thread
From: Ian Lance Taylor @ 2020-12-22 20:13 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:3b2d8145a4c349058d76ce299ea7eea605572004
commit r11-6308-g3b2d8145a4c349058d76ce299ea7eea605572004
Author: Ian Lance Taylor <iant@golang.org>
Date: Mon Dec 21 21:20:59 2020 -0800
runtime: add "success" field to sudog
This is the gofrontend version of https://golang.org/cl/245019.
Original CL description:
The current wakeup protocol for channel communications is that the
second goroutine sets gp.param to the sudog when a value is
successfully communicated over the channel, and to nil when the wakeup
is due to closing the channel.
Setting nil to indicate channel closure works okay for chansend and
chanrecv, because they're only communicating with one channel, so they
know it must be the channel that was closed. However, it means
selectgo has to re-poll all of the channels to figure out which one
was closed.
This commit adds a "success" field to sudog, and changes the wakeup
protocol to always set gp.param to sg, and to use sg.success to
indicate successful communication vs channel closure.
While here, this also reorganizes the chansend code slightly so that
the sudog is still released to the pool if the send blocks and then is
awoken because the channel closed.
For golang/go#40410
This is being brought over to gofrontend as a step toward upgrading to
Go1.16beta1, setting up for more compiler changes related to select handling.
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/279734
Diff:
---
gcc/go/gofrontend/MERGE | 2 +-
libgo/go/runtime/chan.go | 25 +++++++++++++++----------
libgo/go/runtime/runtime2.go | 6 ++++++
libgo/go/runtime/select.go | 19 +++++++------------
4 files changed, 29 insertions(+), 23 deletions(-)
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)
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2020-12-22 20:13 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-12-22 20:13 [gcc r11-6308] runtime: add "success" field to sudog Ian Lance Taylor
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).