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runtime: factor waiting on mark phase

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There are three places where we wait for the GC mark phase to
complete. Factor these all into a single helper function.

Fixes #24362.

Change-Id: I47f6a7147974f5b9a2869c527a024519070ba6f3
Reviewed-on: https://go-review.googlesource.com/102605
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2018-03-26 17:44:05 -04:00
parent f4412aee74
commit fcb7488add
1 changed files with 32 additions and 35 deletions
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67
src/runtime/mgc.go
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@ -231,21 +231,10 @@ func setGCPercent(in int32) (out int32) {
gcSetTriggerRatio(memstats.triggerRatio)
unlock(&mheap_.lock)
// If we just disabled GC, wait for any concurrent GC to
// If we just disabled GC, wait for any concurrent GC mark to
// finish so we always return with no GC running.
if in < 0 {
// Disable phase transitions.
lock(&work.sweepWaiters.lock)
if gcphase == _GCmark {
// GC is active. Wait until we reach sweeping.
gp := getg()
gp.schedlink = work.sweepWaiters.head
work.sweepWaiters.head.set(gp)
goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
} else {
// GC isn't active.
unlock(&work.sweepWaiters.lock)
}
gcWaitOnMark(atomic.Load(&work.cycles))
}
return out
@ -1090,21 +1079,10 @@ func GC() {
// GC may move ahead on its own. For example, when we block
// until mark termination N, we may wake up in cycle N+2.
gp := getg()
// Prevent the GC phase or cycle count from changing.
lock(&work.sweepWaiters.lock)
// Wait until the current sweep termination, mark, and mark
// termination complete.
n := atomic.Load(&work.cycles)
if gcphase == _GCmark {
// Wait until sweep termination, mark, and mark
// termination of cycle N complete.
gp.schedlink = work.sweepWaiters.head
work.sweepWaiters.head.set(gp)
goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
} else {
// We're in sweep N already.
unlock(&work.sweepWaiters.lock)
}
gcWaitOnMark(n)
// We're now in sweep N or later. Trigger GC cycle N+1, which
// will first finish sweep N if necessary and then enter sweep
@ -1112,14 +1090,7 @@ func GC() {
gcStart(gcBackgroundMode, gcTrigger{kind: gcTriggerCycle, n: n + 1})
// Wait for mark termination N+1 to complete.
lock(&work.sweepWaiters.lock)
if gcphase == _GCmark && atomic.Load(&work.cycles) == n+1 {
gp.schedlink = work.sweepWaiters.head
work.sweepWaiters.head.set(gp)
goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
} else {
unlock(&work.sweepWaiters.lock)
}
gcWaitOnMark(n + 1)
// Finish sweep N+1 before returning. We do this both to
// complete the cycle and because runtime.GC() is often used
@ -1156,6 +1127,32 @@ func GC() {
releasem(mp)
}
// gcWaitOnMark blocks until GC finishes the Nth mark phase. If GC has
// already completed this mark phase, it returns immediately.
func gcWaitOnMark(n uint32) {
for {
// Disable phase transitions.
lock(&work.sweepWaiters.lock)
nMarks := atomic.Load(&work.cycles)
if gcphase != _GCmark {
// We've already completed this cycle's mark.
nMarks++
}
if nMarks > n {
// We're done.
unlock(&work.sweepWaiters.lock)
return
}
// Wait until sweep termination, mark, and mark
// termination of cycle N complete.
gp := getg()
gp.schedlink = work.sweepWaiters.head
work.sweepWaiters.head.set(gp)
goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
}
}
// gcMode indicates how concurrent a GC cycle should be.
type gcMode int