gcc/libgo/runtime/lfstack.goc

// 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
#include "runtime.h"
#include "arch.h"

#if __SIZEOF_POINTER__ == 8
// SPARC64 and Solaris on AMD64 uses all 64 bits of virtual addresses.
// Use low-order three bits as ABA counter.
// http://docs.oracle.com/cd/E19120-01/open.solaris/816-5138/6mba6ua5p/index.html
# if defined(__sparc__) || (defined(__sun__) && defined(__amd64__))
static inline uint64 lfPack(LFNode *node, uintptr cnt) {
	return ((uint64)(node)) | ((cnt)&7);
}
static inline LFNode* lfUnpack(uint64 val) {
	return (LFNode*)(val&~7);
}
# else
#  if defined(__aarch64__)
// Depending on the kernel options, pointers on arm64 can have up to 48 significant
// bits (see https://www.kernel.org/doc/Documentation/arm64/memory.txt).
#   define PTR_BITS 48
#  else
// Amd64 uses 48-bit virtual addresses, 47-th bit is used as kernel/user flag.
// So we use 17msb of pointers as ABA counter.
#   define PTR_BITS 47
#  endif
# define CNT_BITS (64 - PTR_BITS + 3)
static inline uint64 lfPack(LFNode *node, uintptr cnt) {
	return ((uint64)(node)<<(64-PTR_BITS)) | (cnt&(((1<<CNT_BITS)-1)));
}
static inline LFNode* lfUnpack(uint64 val) {
	return (LFNode*)((val >> CNT_BITS) << 3);
}
# endif
#else
static inline uint64 lfPack(LFNode *node, uintptr cnt) {
	return ((uint64)(uintptr)(node)<<32) | cnt;
}
static inline LFNode* lfUnpack(uint64 val) {
	return (LFNode*)(uintptr)(val >> 32);
}
#endif

void
runtime_lfstackpush(uint64 *head, LFNode *node)
{
	uint64 old, new;

	if(node != lfUnpack(lfPack(node, 0))) {
		runtime_printf("p=%p\n", node);
		runtime_throw("runtime_lfstackpush: invalid pointer");
	}

	node->pushcnt++;
	new = lfPack(node, node->pushcnt);
	for(;;) {
		old = runtime_atomicload64(head);
		node->next = lfUnpack(old);
		if(runtime_cas64(head, old, new))
			break;
	}
}

LFNode*
runtime_lfstackpop(uint64 *head)
{
	LFNode *node, *node2;
	uint64 old, new;

	for(;;) {
		old = runtime_atomicload64(head);
		if(old == 0)
			return nil;
		node = lfUnpack(old);
		node2 = runtime_atomicloadp(&node->next);
		new = 0;
		if(node2 != nil)
			new = lfPack(node2, node2->pushcnt);
		if(runtime_cas64(head, old, new))
			return node;
	}
}

func lfstackpush_go(head *uint64, node *LFNode) {
	runtime_lfstackpush(head, node);
}

func lfstackpop_go(head *uint64) (node *LFNode) {
	node = runtime_lfstackpop(head);
}