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
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
|
#include "alloc.h"
#include "byte.h"
#include "uint32.h"
#include "exit.h"
#include "tai.h"
#include "cache.h"
uint64 cache_motion = 0;
static char *x = 0;
static uint32 size;
static uint32 hsize;
static uint32 writer;
static uint32 oldest;
static uint32 unused;
/*
100 <= size <= 1000000000.
4 <= hsize <= size/16.
hsize is a power of 2.
hsize <= writer <= oldest <= unused <= size.
If oldest == unused then unused == size.
x is a hash table with the following structure:
x[0...hsize-1]: hsize/4 head links.
x[hsize...writer-1]: consecutive entries, newest entry on the right.
x[writer...oldest-1]: free space for new entries.
x[oldest...unused-1]: consecutive entries, oldest entry on the left.
x[unused...size-1]: unused.
Each hash bucket is a linked list containing the following items:
the head link, the newest entry, the second-newest entry, etc.
Each link is a 4-byte number giving the xor of
the positions of the adjacent items in the list.
Entries are always inserted immediately after the head and removed at the tail.
Each entry contains the following information:
4-byte link; 4-byte keylen; 4-byte datalen; 8-byte expire time; key; data.
*/
#define MAXKEYLEN 1000
#define MAXDATALEN 1000000
static void cache_impossible(void)
{
_exit(111);
}
static void set4(uint32 pos,uint32 u)
{
if (pos > size - 4) cache_impossible();
uint32_pack(x + pos,u);
}
static uint32 get4(uint32 pos)
{
uint32 result;
if (pos > size - 4) cache_impossible();
uint32_unpack(x + pos,&result);
return result;
}
static unsigned int hash(const char *key,unsigned int keylen)
{
unsigned int result = 5381;
while (keylen) {
result = (result << 5) + result;
result ^= (unsigned char) *key;
++key;
--keylen;
}
result <<= 2;
result &= hsize - 4;
return result;
}
char *cache_get(const char *key,unsigned int keylen,unsigned int *datalen,uint32 *ttl)
{
struct tai expire;
struct tai now;
uint32 pos;
uint32 prevpos;
uint32 nextpos;
uint32 u;
unsigned int loop;
double d;
if (!x) return 0;
if (keylen > MAXKEYLEN) return 0;
prevpos = hash(key,keylen);
pos = get4(prevpos);
loop = 0;
while (pos) {
if (get4(pos + 4) == keylen) {
if (pos + 20 + keylen > size) cache_impossible();
if (byte_equal(key,keylen,x + pos + 20)) {
tai_unpack(x + pos + 12,&expire);
tai_now(&now);
if (tai_less(&expire,&now)) return 0;
tai_sub(&expire,&expire,&now);
d = tai_approx(&expire);
if (d > 604800) d = 604800;
*ttl = d;
u = get4(pos + 8);
if (u > size - pos - 20 - keylen) cache_impossible();
*datalen = u;
return x + pos + 20 + keylen;
}
}
nextpos = prevpos ^ get4(pos);
prevpos = pos;
pos = nextpos;
if (++loop > 100) return 0; /* to protect against hash flooding */
}
return 0;
}
void cache_set(const char *key,unsigned int keylen,const char *data,unsigned int datalen,uint32 ttl)
{
struct tai now;
struct tai expire;
unsigned int entrylen;
unsigned int keyhash;
uint32 pos;
if (!x) return;
if (keylen > MAXKEYLEN) return;
if (datalen > MAXDATALEN) return;
if (!ttl) return;
if (ttl > 604800) ttl = 604800;
entrylen = keylen + datalen + 20;
while (writer + entrylen > oldest) {
if (oldest == unused) {
if (writer <= hsize) return;
unused = writer;
oldest = hsize;
writer = hsize;
}
pos = get4(oldest);
set4(pos,get4(pos) ^ oldest);
oldest += get4(oldest + 4) + get4(oldest + 8) + 20;
if (oldest > unused) cache_impossible();
if (oldest == unused) {
unused = size;
oldest = size;
}
}
keyhash = hash(key,keylen);
tai_now(&now);
tai_uint(&expire,ttl);
tai_add(&expire,&expire,&now);
pos = get4(keyhash);
if (pos)
set4(pos,get4(pos) ^ keyhash ^ writer);
set4(writer,pos ^ keyhash);
set4(writer + 4,keylen);
set4(writer + 8,datalen);
tai_pack(x + writer + 12,&expire);
byte_copy(x + writer + 20,keylen,key);
byte_copy(x + writer + 20 + keylen,datalen,data);
set4(keyhash,writer);
writer += entrylen;
cache_motion += entrylen;
}
int cache_init(unsigned int cachesize)
{
if (x) {
alloc_free(x);
x = 0;
}
if (cachesize > 1000000000) cachesize = 1000000000;
if (cachesize < 100) cachesize = 100;
size = cachesize;
hsize = 4;
while (hsize <= (size >> 5)) hsize <<= 1;
x = alloc(size);
if (!x) return 0;
byte_zero(x,size);
writer = hsize;
oldest = size;
unused = size;
return 1;
}
|
