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Source file src/runtime/lfstack.go

Documentation: runtime

  // 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
  // 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: 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
  }
  

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