runtime: copy lfstack code from Go 1.7 runtime

    
    Note that lfstack_64bit.go was modified for Solaris support in a
    different, and better, way than the superseded lfstack.goc code.
    
    Reviewed-on: https://go-review.googlesource.com/31673

From-SVN: r241427

1 files changed, 50 insertions, 0 deletions

diff --git a/libgo/go/runtime/lfstack.go b/libgo/go/runtime/lfstack.go
new file mode 100644
index 0000000..2f2958c
--- /dev/null
+++ b/libgo/go/runtime/lfstack.go
@@ -0,0 +1,50 @@
+// 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.
+// Initialize head to 0, compare with 0 to test for emptiness.
+// The stack does not keep pointers to nodes,
+// so they can be garbage collected if there are no other pointers to nodes.
+// The following code runs only in non-preemptible contexts.
+
+package runtime
+
+import (
+	"runtime/internal/atomic"
+	"unsafe"
+)
+
+// Temporary for C code to call:
+//go:linkname lfstackpush runtime.lfstackpush
+//go:linkname lfstackpop runtime.lfstackpop
+
+func lfstackpush(head *uint64, node *lfnode) {
+	node.pushcnt++
+	new := lfstackPack(node, node.pushcnt)
+	if node1 := lfstackUnpack(new); node1 != node {
+		print("runtime: lfstackpush invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
+		throw("lfstackpush")
+	}
+	for {
+		old := atomic.Load64(head)
+		node.next = old
+		if atomic.Cas64(head, old, new) {
+			break
+		}
+	}
+}
+
+func lfstackpop(head *uint64) unsafe.Pointer {
+	for {
+		old := atomic.Load64(head)
+		if old == 0 {
+			return nil
+		}
+		node := lfstackUnpack(old)
+		next := atomic.Load64(&node.next)
+		if atomic.Cas64(head, old, next) {
+			return unsafe.Pointer(node)
+		}
+	}
+}