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runtime: introduce a type for lfstacks

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The lfstack API is still a C-style API: lfstacks all have unhelpful
type uint64 and the APIs are package-level functions. Make the code
more readable and Go-style by creating an lfstack type with methods
for push, pop, and empty.

Change-Id: I64685fa3be0e82ae2d1a782a452a50974440a827
Reviewed-on: https://go-review.googlesource.com/38290
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2017-03-07 16:38:29 -05:00
parent 2805d20689
commit 13ae271d5d
4 changed files with 35 additions and 24 deletions
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35
src/runtime/lfstack.go
View file

@ -3,10 +3,6 @@
// 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
@ -15,32 +11,47 @@ import (
"unsafe"
)
func lfstackpush(head *uint64, node *lfnode) {
// 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
// is responsible for ensuring the nodes are not garbage collected
// (typically by allocating them from manually-managed memory).
type lfstack uint64
func (head *lfstack) push(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")
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(head)
old := atomic.Load64((*uint64)(head))
node.next = old
if atomic.Cas64(head, old, new) {
if atomic.Cas64((*uint64)(head), old, new) {
break
}
}
}
func lfstackpop(head *uint64) unsafe.Pointer {
func (head *lfstack) pop() unsafe.Pointer {
for {
old := atomic.Load64(head)
old := atomic.Load64((*uint64)(head))
if old == 0 {
return nil
}
node := lfstackUnpack(old)
next := atomic.Load64(&node.next)
if atomic.Cas64(head, old, next) {
if atomic.Cas64((*uint64)(head), old, next) {
return unsafe.Pointer(node)
}
}
}
func (head *lfstack) empty() bool {
return atomic.Load64((*uint64)(head)) == 0
}