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runtime: rename m.gcing to m.preemptoff and make it a string

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m.gcing has become overloaded to mean "don't preempt this g" in
general.  Once the garbage collector is preemptible, the one thing it
*won't* mean is that we're in the garbage collector.

So, rename gcing to "preemptoff" and make it a string giving a reason
that preemption is disabled.  gcing was never set to anything but 0 or
1, so we don't have to worry about there being a stack of reasons.

Change-Id: I4337c29e8e942e7aa4f106fc29597e1b5de4ef46
Reviewed-on: https://go-review.googlesource.com/3660
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Austin Clements 2015-01-30 15:30:41 -05:00
parent f95becaddb
commit 28b5118415
13 changed files with 36 additions and 32 deletions
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9
src/runtime/stack1.go
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@ -208,7 +208,7 @@ func stackalloc(n uint32) stack {
}
var x gclinkptr
c := thisg.m.mcache
if c == nil || thisg.m.gcing != 0 || thisg.m.helpgc != 0 {
if c == nil || thisg.m.preemptoff != "" || thisg.m.helpgc != 0 {
// c == nil can happen in the guts of exitsyscall or
// procresize. Just get a stack from the global pool.
// Also don't touch stackcache during gc
@ -271,7 +271,7 @@ func stackfree(stk stack) {
}
x := gclinkptr(v)
c := gp.m.mcache
if c == nil || gp.m.gcing != 0 || gp.m.helpgc != 0 {
if c == nil || gp.m.preemptoff != "" || gp.m.helpgc != 0 {
lock(&stackpoolmu)
stackpoolfree(x, order)
unlock(&stackpoolmu)
@ -648,7 +648,8 @@ func newstack() {
// Be conservative about where we preempt.
// We are interested in preempting user Go code, not runtime code.
// If we're holding locks, mallocing, or GCing, don't preempt.
// If we're holding locks, mallocing, or preemption is disabled, don't
// preempt.
// This check is very early in newstack so that even the status change
// from Grunning to Gwaiting and back doesn't happen in this case.
// That status change by itself can be viewed as a small preemption,
@ -658,7 +659,7 @@ func newstack() {
// it needs a lock held by the goroutine), that small preemption turns
// into a real deadlock.
if preempt {
if thisg.m.locks != 0 || thisg.m.mallocing != 0 || thisg.m.gcing != 0 || thisg.m.p.status != _Prunning {
if thisg.m.locks != 0 || thisg.m.mallocing != 0 || thisg.m.preemptoff != "" || thisg.m.p.status != _Prunning {
// Let the goroutine keep running for now.
// gp->preempt is set, so it will be preempted next time.
gp.stackguard0 = gp.stack.lo + _StackGuard