@@ -721,9 +721,13 @@ func casgstatus(gp *g, oldval, newval uint32) {
721721 throw ("casgstatus" )
722722 }
723723
724+ // See http://golang.org/cl/21503 for justification of the yield delay.
725+ const yieldDelay = 5 * 1000
726+ var nextYield int64
727+
724728 // loop if gp->atomicstatus is in a scan state giving
725729 // GC time to finish and change the state to oldval.
726- for ! atomic .Cas (& gp .atomicstatus , oldval , newval ) {
730+ for i := 0 ; ! atomic .Cas (& gp .atomicstatus , oldval , newval ); i ++ {
727731 if oldval == _Gwaiting && gp .atomicstatus == _Grunnable {
728732 systemstack (func () {
729733 throw ("casgstatus: waiting for Gwaiting but is Grunnable" )
@@ -736,6 +740,18 @@ func casgstatus(gp *g, oldval, newval uint32) {
736740 // gcphasework(gp)
737741 // })
738742 // }
743+ // But meanwhile just yield.
744+ if i == 0 {
745+ nextYield = nanotime () + yieldDelay
746+ }
747+ if nanotime () < nextYield {
748+ for x := 0 ; x < 10 && gp .atomicstatus != oldval ; x ++ {
749+ procyield (1 )
750+ }
751+ } else {
752+ osyield ()
753+ nextYield = nanotime () + yieldDelay / 2
754+ }
739755 }
740756 if newval == _Grunning {
741757 gp .gcscanvalid = false
@@ -773,12 +789,17 @@ func scang(gp *g) {
773789
774790 gp .gcscandone = false
775791
792+ // See http://golang.org/cl/21503 for justification of the yield delay.
793+ const yieldDelay = 10 * 1000
794+ var nextYield int64
795+
776796 // Endeavor to get gcscandone set to true,
777797 // either by doing the stack scan ourselves or by coercing gp to scan itself.
778798 // gp.gcscandone can transition from false to true when we're not looking
779799 // (if we asked for preemption), so any time we lock the status using
780800 // castogscanstatus we have to double-check that the scan is still not done.
781- for ! gp .gcscandone {
801+ loop:
802+ for i := 0 ; ! gp .gcscandone ; i ++ {
782803 switch s := readgstatus (gp ); s {
783804 default :
784805 dumpgstatus (gp )
@@ -787,6 +808,7 @@ func scang(gp *g) {
787808 case _Gdead :
788809 // No stack.
789810 gp .gcscandone = true
811+ break loop
790812
791813 case _Gcopystack :
792814 // Stack being switched. Go around again.
@@ -802,6 +824,7 @@ func scang(gp *g) {
802824 gp .gcscandone = true
803825 }
804826 restartg (gp )
827+ break loop
805828 }
806829
807830 case _Gscanwaiting :
@@ -827,6 +850,16 @@ func scang(gp *g) {
827850 casfrom_Gscanstatus (gp , _Gscanrunning , _Grunning )
828851 }
829852 }
853+
854+ if i == 0 {
855+ nextYield = nanotime () + yieldDelay
856+ }
857+ if nanotime () < nextYield {
858+ procyield (10 )
859+ } else {
860+ osyield ()
861+ nextYield = nanotime () + yieldDelay / 2
862+ }
830863 }
831864
832865 gp .preemptscan = false // cancel scan request if no longer needed
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