github.com/panjjo/go@v0.0.0-20161104043856-d62b31386338/src/runtime/lfstack.go (about)

     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  func lfstackpush(head *uint64, node *lfnode) {
    19  	node.pushcnt++
    20  	new := lfstackPack(node, node.pushcnt)
    21  	if node1 := lfstackUnpack(new); node1 != node {
    22  		print("runtime: lfstackpush invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
    23  		throw("lfstackpush")
    24  	}
    25  	for {
    26  		old := atomic.Load64(head)
    27  		node.next = old
    28  		if atomic.Cas64(head, old, new) {
    29  			break
    30  		}
    31  	}
    32  }
    33  
    34  func lfstackpop(head *uint64) unsafe.Pointer {
    35  	for {
    36  		old := atomic.Load64(head)
    37  		if old == 0 {
    38  			return nil
    39  		}
    40  		node := lfstackUnpack(old)
    41  		next := atomic.Load64(&node.next)
    42  		if atomic.Cas64(head, old, next) {
    43  			return unsafe.Pointer(node)
    44  		}
    45  	}
    46  }