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, 67 insertions, 0 deletions

diff --git a/src/runtime/internal/atomic/atomic_test.go b/src/runtime/internal/atomic/atomic_test.go
new file mode 100644
index 0000000000..e8ec788d6a
--- /dev/null
+++ b/src/runtime/internal/atomic/atomic_test.go
@@ -0,0 +1,67 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package atomic_test
+
+import (
+	"runtime"
+	"runtime/internal/atomic"
+	"testing"
+	"unsafe"
+)
+
+func runParallel(N, iter int, f func()) {
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(int(N)))
+	done := make(chan bool)
+	for i := 0; i < N; i++ {
+		go func() {
+			for j := 0; j < iter; j++ {
+				f()
+			}
+			done <- true
+		}()
+	}
+	for i := 0; i < N; i++ {
+		<-done
+	}
+}
+
+func TestXadduintptr(t *testing.T) {
+	const N = 20
+	const iter = 100000
+	inc := uintptr(100)
+	total := uintptr(0)
+	runParallel(N, iter, func() {
+		atomic.Xadduintptr(&total, inc)
+	})
+	if want := uintptr(N * iter * inc); want != total {
+		t.Fatalf("xadduintpr error, want %d, got %d", want, total)
+	}
+	total = 0
+	runParallel(N, iter, func() {
+		atomic.Xadduintptr(&total, inc)
+		atomic.Xadduintptr(&total, uintptr(-int64(inc)))
+	})
+	if total != 0 {
+		t.Fatalf("xadduintpr total error, want %d, got %d", 0, total)
+	}
+}
+
+// Tests that xadduintptr correctly updates 64-bit values.  The place where
+// we actually do so is mstats.go, functions mSysStat{Inc,Dec}.
+func TestXadduintptrOnUint64(t *testing.T) {
+	/*	if runtime.BigEndian != 0 {
+		// On big endian architectures, we never use xadduintptr to update
+		// 64-bit values and hence we skip the test.  (Note that functions
+		// mSysStat{Inc,Dec} in mstats.go have explicit checks for
+		// big-endianness.)
+		return
+	}*/
+	const inc = 100
+	val := uint64(0)
+	atomic.Xadduintptr((*uintptr)(unsafe.Pointer(&val)), inc)
+	if inc != val {
+		t.Fatalf("xadduintptr should increase lower-order bits, want %d, got %d", inc, val)
+	}
+}