runtime: add lock-free stack

This is factored out part of the:
https://golang.org/cl/5279048/
(parallel GC)

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5993043

1 files changed, 64 insertions, 0 deletions

diff --git a/src/pkg/runtime/lfstack.c b/src/pkg/runtime/lfstack.c
new file mode 100644
index 0000000000..e4ea6e83da
--- /dev/null
+++ b/src/pkg/runtime/lfstack.c
@@ -0,0 +1,64 @@
+// Copyright 2012 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.
+
+// Lock-free stack.
+
+#include "runtime.h"
+#include "arch_GOARCH.h"
+
+#ifdef _64BIT
+// Amd64 uses 48-bit virtual addresses, 47-th bit is used as kernel/user flag.
+// So we use 17msb of pointers as ABA counter.
+# define PTR_BITS 47
+#else
+# define PTR_BITS 32
+#endif
+#define PTR_MASK ((1ull<<PTR_BITS)-1)
+
+void
+runtime·lfstackpush(uint64 *head, LFNode *node)
+{
+	uint64 old, new;
+
+	if((uint64)node != ((uint64)node&PTR_MASK)) {
+		runtime·printf("p=%p\n", node);
+		runtime·throw("runtime·lfstackpush: invalid pointer");
+	}
+
+	node->pushcnt++;
+	new = (uint64)node|(((uint64)node->pushcnt)<<PTR_BITS);
+	old = runtime·atomicload64(head);
+	for(;;) {
+		node->next = (LFNode*)(old&PTR_MASK);
+		if(runtime·cas64(head, &old, new))
+			break;
+	}
+}
+
+LFNode*
+runtime·lfstackpop(uint64 *head)
+{
+	LFNode *node, *node2;
+	uint64 old, new;
+
+	old = runtime·atomicload64(head);
+	for(;;) {
+		if(old == 0)
+			return nil;
+		node = (LFNode*)(old&PTR_MASK);
+		node2 = runtime·atomicloadp(&node->next);
+		new = 0;
+		if(node2 != nil)
+			new = (uint64)node2|(((uint64)node2->pushcnt)<<PTR_BITS);
+		if(runtime·cas64(head, &old, new))
+			return node;
+	}
+}
+
+void
+runtime·lfstackpop2(uint64 *head, LFNode *node)
+{
+	node = runtime·lfstackpop(head);
+	FLUSH(&node);
+}