libgo/go/runtime/lfstack.go

   1 // Copyright 2012 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Lock-free stack.
   6 // Initialize head to 0, compare with 0 to test for emptiness.
   7 // The stack does not keep pointers to nodes,
   8 // so they can be garbage collected if there are no other pointers to nodes.
   9 // The following code runs only in non-preemptible contexts.
  10
  11 package runtime
  12
  13 import (
  14         "runtime/internal/atomic"
  15         "unsafe"
  16 )
  17
  18 // Temporary for C code to call:
  19 //go:linkname lfstackpush runtime.lfstackpush
  20 //go:linkname lfstackpop runtime.lfstackpop
  21
  22 func lfstackpush(head *uint64, node *lfnode) {
  23         node.pushcnt++
  24         new := lfstackPack(node, node.pushcnt)
  25         if node1 := lfstackUnpack(new); node1 != node {
  26                 print("runtime: lfstackpush invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
  27                 throw("lfstackpush")
  28         }
  29         for {
  30                 old := atomic.Load64(head)
  31                 node.next = old
  32                 if atomic.Cas64(head, old, new) {
  33                         break
  34                 }
  35         }
  36 }
  37
  38 func lfstackpop(head *uint64) unsafe.Pointer {
  39         for {
  40                 old := atomic.Load64(head)
  41                 if old == 0 {
  42                         return nil
  43                 }
  44                 node := lfstackUnpack(old)
  45                 next := atomic.Load64(&node.next)
  46                 if atomic.Cas64(head, old, next) {
  47                         return unsafe.Pointer(node)
  48                 }
  49         }
  50 }