1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "common.h"
#include <algorithm>
namespace vespamalloc {
/**
* @brief Pointer and tag - use instead of bare pointer for cmpSwap()
*
* When making a lock-free data structure by using cmpSwap
* on pointers, you'll often run into the "ABA problem", see
* http://en.wikipedia.org/wiki/ABA_problem for details.
* The TaggedPtr makes it easy to do the woraround with tag bits,
* but requires the double-word compare-and-swap instruction.
* Very early Amd K7/8 CPUs are lacking this and will fail (Illegal Instruction).
**/
struct TaggedPtr {
TaggedPtr() noexcept : _ptr(nullptr), _tag(0) { }
TaggedPtr(void *h, size_t t) noexcept : _ptr(h), _tag(t) {}
void *_ptr;
size_t _tag;
};
class AFListBase
{
public:
using HeadPtr = TaggedPtr;
using AtomicHeadPtr = std::atomic<HeadPtr>;
AFListBase() : _next(NULL) { }
void setNext(AFListBase * csl) { _next = csl; }
static void init();
static void linkInList(AtomicHeadPtr & head, AFListBase * list);
static void linkIn(AtomicHeadPtr & head, AFListBase * csl, AFListBase * tail);
protected:
AFListBase * getNext() { return _next; }
static AFListBase * linkOut(AtomicHeadPtr & head);
private:
AFListBase *_next;
};
template <typename MemBlockPtrT>
class AFList : public AFListBase
{
public:
typedef size_t CountT;
enum { NumBlocks = 126 };
AFList() : _count(0) { }
CountT count() const { return _count; }
void add(MemBlockPtrT & ptr) {
ptr.free();
PARANOID_CHECK2( if (full()) { *(int*)0=0; });
_memBlockList[_count++] = ptr;
}
void sub(MemBlockPtrT & mem) {
if (empty()) {
return;
}
mem = _memBlockList[--_count];
}
bool empty() const { return (_count == 0); }
bool full() const { return (_count == NumBlocks); }
size_t fill(void * mem, SizeClassT sc, size_t blocksPerChunk = NumBlocks);
AFList * getNext() { return static_cast<AFList *>(AFListBase::getNext()); }
static AFList * linkOut(AtomicHeadPtr & head) {
return static_cast<AFList *>(AFListBase::linkOut(head));
}
private:
CountT _count;
MemBlockPtrT _memBlockList[NumBlocks];
};
template <typename MemBlockPtrT>
size_t AFList<MemBlockPtrT>::fill(void * mem, SizeClassT sc, size_t blocksPerChunk)
{
size_t sz = MemBlockPtrT::classSize(sc);
int retval(std::max(0, int(blocksPerChunk-_count)));
char * first = (char *) mem;
for(int i=0; i < retval; i++) {
_memBlockList[_count] = MemBlockPtrT(first + i*sz, MemBlockPtrT::unAdjustSize(sz));
_memBlockList[_count].free();
_count++;
}
return retval;
}
}
|
