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Source file src/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	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	}
    47	

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