runtime: break atomics out into package runtime/internal/atomic

This change breaks out most of the atomics functions in the runtime
into package runtime/internal/atomic. It adds some basic support
in the toolchain for runtime packages, and also modifies linux/arm
atomics to remove the dependency on the runtime's mutex. The mutexes
have been replaced with spinlocks.

all trybots are happy!
In addition to the trybots, I've tested on the darwin/arm64 builder,
on the darwin/arm builder, and on a ppc64le machine.

Change-Id: I6698c8e3cf3834f55ce5824059f44d00dc8e3c2f
Reviewed-on: https://go-review.googlesource.com/14204
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/src/runtime/cpuprof.go b/src/runtime/cpuprof.go
index 0790852d97..87d5f99b44 100644
--- a/src/runtime/cpuprof.go
+++ b/src/runtime/cpuprof.go
@@ -50,7 +50,10 @@
 
 package runtime
 
-import "unsafe"
+import (
+	"runtime/internal/atomic"
+	"unsafe"
+)
 
 const (
 	numBuckets      = 1 << 10
@@ -173,7 +176,7 @@ func SetCPUProfileRate(hz int) {
 			if n&0x80000000 != 0 {
 				print("runtime: setcpuprofile(off) twice\n")
 			}
-			if cas(&cpuprof.handoff, n, n|0x80000000) {
+			if atomic.Cas(&cpuprof.handoff, n, n|0x80000000) {
 				if n == 0 {
 					// we did the transition from 0 -> nonzero so we wake getprofile
 					notewakeup(&cpuprof.wait)
@@ -276,7 +279,7 @@ func (p *cpuProfile) evict(e *cpuprofEntry) bool {
 // so it cannot allocate memory or block.  It can try to swap logs with
 // the writing goroutine, as explained in the comment at the top of this file.
 func (p *cpuProfile) flushlog() bool {
-	if !cas(&p.handoff, 0, uint32(p.nlog)) {
+	if !atomic.Cas(&p.handoff, 0, uint32(p.nlog)) {
 		return false
 	}
 	notewakeup(&p.wait)
@@ -318,7 +321,7 @@ func (p *cpuProfile) getprofile() []byte {
 				p.flushing = true
 				goto Flush
 			}
-			if cas(&p.handoff, n, 0) {
+			if atomic.Cas(&p.handoff, n, 0) {
 				break
 			}
 		}
@@ -389,7 +392,7 @@ Flush:
 
 	// Finally done.  Clean up and return nil.
 	p.flushing = false
-	if !cas(&p.handoff, p.handoff, 0) {
+	if !atomic.Cas(&p.handoff, p.handoff, 0) {
 		print("runtime: profile flush racing with something\n")
 	}
 	return nil