lfstack.go

Documentation: runtime

		 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  
		 7  package runtime
		 8  
		 9  import (
		10  	"runtime/internal/atomic"
		11  	"unsafe"
		12  )
		13  
		14  // lfstack is the head of a lock-free stack.
		15  //
		16  // The zero value of lfstack is an empty list.
		17  //
		18  // This stack is intrusive. Nodes must embed lfnode as the first field.
		19  //
		20  // The stack does not keep GC-visible pointers to nodes, so the caller
		21  // is responsible for ensuring the nodes are not garbage collected
		22  // (typically by allocating them from manually-managed memory).
		23  type lfstack uint64
		24  
		25  func (head *lfstack) push(node *lfnode) {
		26  	node.pushcnt++
		27  	new := lfstackPack(node, node.pushcnt)
		28  	if node1 := lfstackUnpack(new); node1 != node {
		29  		print("runtime: lfstack.push invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
		30  		throw("lfstack.push")
		31  	}
		32  	for {
		33  		old := atomic.Load64((*uint64)(head))
		34  		node.next = old
		35  		if atomic.Cas64((*uint64)(head), old, new) {
		36  			break
		37  		}
		38  	}
		39  }
		40  
		41  func (head *lfstack) pop() unsafe.Pointer {
		42  	for {
		43  		old := atomic.Load64((*uint64)(head))
		44  		if old == 0 {
		45  			return nil
		46  		}
		47  		node := lfstackUnpack(old)
		48  		next := atomic.Load64(&node.next)
		49  		if atomic.Cas64((*uint64)(head), old, next) {
		50  			return unsafe.Pointer(node)
		51  		}
		52  	}
		53  }
		54  
		55  func (head *lfstack) empty() bool {
		56  	return atomic.Load64((*uint64)(head)) == 0
		57  }
		58  
		59  // lfnodeValidate panics if node is not a valid address for use with
		60  // lfstack.push. This only needs to be called when node is allocated.
		61  func lfnodeValidate(node *lfnode) {
		62  	if lfstackUnpack(lfstackPack(node, ^uintptr(0))) != node {
		63  		printlock()
		64  		println("runtime: bad lfnode address", hex(uintptr(unsafe.Pointer(node))))
		65  		throw("bad lfnode address")
		66  	}
		67  }
		68
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