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// 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.
package runtime
import (
"runtime/internal/atomic"
"unsafe"
)
// lfstack is the head of a lock-free stack.
//
// The zero value of lfstack is an empty list.
//
// This stack is intrusive. Nodes must embed lfnode as the first field.
//
// The stack does not keep GC-visible pointers to nodes, so the caller
// must ensure the nodes are allocated outside the Go heap.
type lfstack uint64
func (head *lfstack) push(node *lfnode) {
node.pushcnt++
new := lfstackPack(node, node.pushcnt)
if node1 := lfstackUnpack(new); node1 != node {
print("runtime: lfstack.push invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
throw("lfstack.push")
}
for {
old := atomic.Load64((*uint64)(head))
node.next = old
if atomic.Cas64((*uint64)(head), old, new) {
break
}
}
}
func (head *lfstack) pop() unsafe.Pointer {
for {
old := atomic.Load64((*uint64)(head))
if old == 0 {
return nil
}
node := lfstackUnpack(old)
next := atomic.Load64(&node.next)
if atomic.Cas64((*uint64)(head), old, next) {
return unsafe.Pointer(node)
}
}
}
func (head *lfstack) empty() bool {
return atomic.Load64((*uint64)(head)) == 0
}
// lfnodeValidate panics if node is not a valid address for use with
// lfstack.push. This only needs to be called when node is allocated.
func lfnodeValidate(node *lfnode) {
if base, _, _ := findObject(uintptr(unsafe.Pointer(node)), 0, 0); base != 0 {
throw("lfstack node allocated from the heap")
}
if lfstackUnpack(lfstackPack(node, ^uintptr(0))) != node {
printlock()
println("runtime: bad lfnode address", hex(uintptr(unsafe.Pointer(node))))
throw("bad lfnode address")
}
}
func lfstackPack(node *lfnode, cnt uintptr) uint64 {
return uint64(taggedPointerPack(unsafe.Pointer(node), cnt))
}
func lfstackUnpack(val uint64) *lfnode {
return (*lfnode)(taggedPointer(val).pointer())
}
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