只要接触过c/c++网路编程人都可能会知道select io 模式，网络书籍都说 fd_set {int num; SOCKET arr[64]} 有所限制，因为数组的长度只有64，那么超过64你就不能放，要么你就是用多线程分别实用select.。
一些书籍通过改定义宏 使数组的长度变长，但也不实用，不能动态的变化，我总不能定一个非常的长的长度，毕竟是在栈上。
我就在想那么select完全只能在客户端使用，而且套接字还不能超过64。那这不就是一个软肋吗？？一直对这个有一个迷惑。。。。。
后来，自己看到了libevent的源代码发现他也用的是select。。看别人说这个库，轻轻松松处理上万个套接字，我就在想select不是有限制吗？？他是怎么做到。。。。。。
看了源代码，我明白了。他只是用对上存放SOCKET的句柄。。我们看一下他的新定义结构体。
struct win_fd_set {
u_int fd_count;
SOCKET fd_array[1];
};
这个就是新定义结构体，跟原来稍微有点变化只是把64改为1，有些同学可能见多很多这样的写法，这种写法我也在一些项目使用了。这种写法可以fd_array动态变化。
win_fd_set * Set = (win_fd_set*)malloc(sizeof(win_fd_set) + sizoef(SCOEKT) * 10);
Set->fd_array 可以放11 个 SOCKET，因为我的内存大小足够放11个SOCKET。
请记住内存是没有数据格式，只要足够大小，随便你怎么放。数据格式只是方便我们管理和处理数据而已。
这样就解决64个大小限制。。我其实一直很好奇为什么中国书籍都是一样的，libevent已经出来好久了，但也没有看到有人说这一点，可能是高手们都不屑。
现在渐渐喜欢看开源的代码，不喜欢看书籍了，喜欢在代码中学习他们是怎么组织一个好项目。
有时候感慨：
高手用c 写着漂亮的c++代码，而我等菜鸟却用c++ 写丑陋的c代码。。
我顺便把他整个定义结构和函数给大家贴出来，免大家还要自己去下libevent，不过推荐没有看过libevent同学，可以稍微看一下。
1
volatile
double SIGFPE_REQ = 0.0f;
2
3
struct idx_info {
4
int read_pos_plus1;
5
int write_pos_plus1;
6 };
7
8
struct win32op {
9 unsigned num_fds_in_fd_sets;
10
int resize_out_sets;
11
struct win_fd_set *readset_in;
12
struct win_fd_set *writeset_in;
13
struct win_fd_set *readset_out;
14
struct win_fd_set *writeset_out;
15
struct win_fd_set *exset_out;
16 unsigned signals_are_broken : 1;
17 };
18
19
static
void *win32_init(
struct event_base *);
20
static
int win32_add(
struct event_base *, evutil_socket_t,
short old,
short events,
void *_idx);
21
static
int win32_del(
struct event_base *, evutil_socket_t,
short old,
short events,
void *_idx);
22
static
int win32_dispatch(
struct event_base *
base,
struct timeval *);
23
static
void win32_dealloc(
struct event_base *);
24
25
struct eventop win32ops = {
26 "win32",
27 win32_init,
28 win32_add,
29 win32_del,
30 win32_dispatch,
31 win32_dealloc,
32 0,
/*
doesn't need reinit
*/
33 0,
/*
No features supported.
*/
34
sizeof(
struct idx_info),
35 };
36
37
#define FD_SET_ALLOC_SIZE(n) ((sizeof(struct win_fd_set) + ((n)-1)*sizeof(SOCKET)))
38
39
static
int
40 grow_fd_sets(
struct win32op *op, unsigned new_num_fds)
41 {
42 size_t size;
43
44 EVUTIL_ASSERT(new_num_fds >= op->readset_in->fd_count &&
45 new_num_fds >= op->writeset_in->fd_count);
46 EVUTIL_ASSERT(new_num_fds >= 1);
47
48 size = FD_SET_ALLOC_SIZE(new_num_fds);
49
if (!(op->readset_in = mm_realloc(op->readset_in, size)))
50
return (-1);
51
if (!(op->writeset_in = mm_realloc(op->writeset_in, size)))
52
return (-1);
53 op->resize_out_sets = 1;
54 op->num_fds_in_fd_sets = new_num_fds;
55
return (0);
56 }
57
58
static
int
59 do_fd_set(
struct win32op *op,
struct idx_info *ent, evutil_socket_t s,
int read)
60 {
61
struct win_fd_set *
set = read ? op->readset_in : op->writeset_in;
62
if (read) {
63
if (ent->read_pos_plus1 > 0)
64
return (0);
65 }
else {
66
if (ent->write_pos_plus1 > 0)
67
return (0);
68 }
69
if (
set->fd_count == op->num_fds_in_fd_sets) {
70
if (grow_fd_sets(op, op->num_fds_in_fd_sets*2))
71
return (-1);
72
/*
set pointer will have changed and needs reiniting!
*/
73
set = read ? op->readset_in : op->writeset_in;
74 }
75
set->fd_array[
set->fd_count] = s;
76
if (read)
77 ent->read_pos_plus1 =
set->fd_count+1;
78
else
79 ent->write_pos_plus1 =
set->fd_count+1;
80
return (
set->fd_count++);
81 }
82
83
static
int
84 do_fd_clear(
struct event_base *
base,
85
struct win32op *op,
struct idx_info *ent,
int read)
86 {
87
int i;
88
struct win_fd_set *
set = read ? op->readset_in : op->writeset_in;
89
if (read) {
90 i = ent->read_pos_plus1 - 1;
91 ent->read_pos_plus1 = 0;
92 }
else {
93 i = ent->write_pos_plus1 - 1;
94 ent->write_pos_plus1 = 0;
95 }
96
if (i fd_count != (unsigned)i) {
99
struct idx_info *ent2;
100 SOCKET s2;
101 s2 =
set->fd_array[i] =
set->fd_array[
set->fd_count];
102
103 ent2 = evmap_io_get_fdinfo(&
base->io, s2);
104
105
if (!ent2)
/*
This indicates a bug.
*/
106
return (0);
107
if (read)
108 ent2->read_pos_plus1 = i+1;
109
else
110 ent2->write_pos_plus1 = i+1;
111 }
112
return (0);
113 }
114
115
#define NEVENT 32
116
void *
117 win32_init(
struct event_base *_base)
118 {
119
struct win32op *winop;
120 size_t size;
121
if (!(winop = mm_calloc(1,
sizeof(
struct win32op))))
122
return NULL;
123 winop->num_fds_in_fd_sets = NEVENT;
124 size = FD_SET_ALLOC_SIZE(NEVENT);
125
if (!(winop->readset_in = mm_malloc(size)))
126
goto err;
127
if (!(winop->writeset_in = mm_malloc(size)))
128
goto err;
129
if (!(winop->readset_out = mm_malloc(size)))
130
goto err;
131
if (!(winop->writeset_out = mm_malloc(size)))
132
goto err;
133
if (!(winop->exset_out = mm_malloc(size)))
134
goto err;
135 winop->readset_in->fd_count = winop->writeset_in->fd_count = 0;
136 winop->readset_out->fd_count = winop->writeset_out->fd_count
137 = winop->exset_out->fd_count = 0;
138
139
if (evsig_init(_base) signals_are_broken = 1;
141
142
return (winop);
143 err:
144 XFREE(winop->readset_in);
145 XFREE(winop->writeset_in);
146 XFREE(winop->readset_out);
147 XFREE(winop->writeset_out);
148 XFREE(winop->exset_out);
149 XFREE(winop);
150
return (NULL);
151 }
152
153
int
154 win32_add(
struct event_base *
base, evutil_socket_t fd,
155
short old,
short events,
void *_idx)
156 {
157
struct win32op *win32op =
base->evbase;
158
struct idx_info *idx = _idx;
159
160
if ((events & EV_SIGNAL) && win32op->signals_are_broken)
161
return (-1);
162
163
if (!(events & (EV_READ|EV_WRITE)))
164
return (0);
165
166 event_debug(("%s: adding event for %d", __func__, (
int)fd));
167
if (events & EV_READ) {
168
if (do_fd_set(win32op, idx, fd, 1)fd_count =
in->fd_count;
199 memcpy(
out->fd_array,
in->fd_array,
in->fd_count * (
sizeof(SOCKET)));
200 }
201
202
/*
203
static void dump_fd_set(struct win_fd_set *s)
204
{
205
unsigned int i;
206
printf("[ ");
207
for(i=0;ifd_count;++i)
208
printf("%d ",(int)s->fd_array[i]);
209
printf("]\n");
210
}
211
*/
212
213
int
214 win32_dispatch(
struct event_base *
base,
struct timeval *tv)
215 {
216
struct win32op *win32op =
base->evbase;
217
int res = 0;
218 unsigned j, i;
219
int fd_count;
220 SOCKET s;
221
222
if (win32op->resize_out_sets) {
223 size_t size = FD_SET_ALLOC_SIZE(win32op->num_fds_in_fd_sets);
224
if (!(win32op->readset_out = mm_realloc(win32op->readset_out, size)))
225
return (-1);
226
if (!(win32op->exset_out = mm_realloc(win32op->exset_out, size)))
227
return (-1);
228
if (!(win32op->writeset_out = mm_realloc(win32op->writeset_out, size)))
229
return (-1);
230 win32op->resize_out_sets = 0;
231 }
232
233 fd_set_copy(win32op->readset_out, win32op->readset_in);
234 fd_set_copy(win32op->exset_out, win32op->writeset_in);
235 fd_set_copy(win32op->writeset_out, win32op->writeset_in);
236
237 fd_count =
238 (win32op->readset_out->fd_count > win32op->writeset_out->fd_count) ?
239 win32op->readset_out->fd_count : win32op->writeset_out->fd_count;
240
241
if (!fd_count) {
242
long msec = tv ? evutil_tv_to_msec(tv) : LONG_MAX;
243
/*
Sleep's DWORD argument is unsigned long
*/
244
if (msec readset_out,
255 (
struct fd_set*)win32op->writeset_out,
256 (
struct fd_set*)win32op->exset_out, tv);
257
258 EVBASE_ACQUIRE_LOCK(
base, th_base_lock);
259
260 event_debug(("%s: select returned %d", __func__, res));
261
262
if (res readset_out->fd_count) {
267 i = rand() % win32op->readset_out->fd_count;
268
for (j=0; jreadset_out->fd_count; ++j) {
269
if (++i >= win32op->readset_out->fd_count)
270 i = 0;
271 s = win32op->readset_out->fd_array[i];
272 evmap_io_active(
base, s, EV_READ);
273 }
274 }
275
if (win32op->exset_out->fd_count) {
276 i = rand() % win32op->exset_out->fd_count;
277
for (j=0; jexset_out->fd_count; ++j) {
278
if (++i >= win32op->exset_out->fd_count)
279 i = 0;
280 s = win32op->exset_out->fd_array[i];
281 evmap_io_active(
base, s, EV_WRITE);
282 }
283 }
284
if (win32op->writeset_out->fd_count) {
285 SOCKET s;
286 i = rand() % win32op->writeset_out->fd_count;
287
for (j=0; jwriteset_out->fd_count; ++j) {
288
if (++i >= win32op->writeset_out->fd_count)
289 i = 0;
290 s = win32op->writeset_out->fd_array[i];
291 evmap_io_active(
base, s, EV_WRITE);
292 }
293 }
294
return (0);
295 }
296
297
void
298 win32_dealloc(
struct event_base *_base)
299 {
300
struct win32op *win32op = _base->evbase;
301
302 evsig_dealloc(_base);
303
if (win32op->readset_in)
304 mm_free(win32op->readset_in);
305
if (win32op->writeset_in)
306 mm_free(win32op->writeset_in);
307
if (win32op->readset_out)
308 mm_free(win32op->readset_out);
309
if (win32op->writeset_out)
310 mm_free(win32op->writeset_out);
311
if (win32op->exset_out)
312 mm_free(win32op->exset_out);
313
/*
XXXXX free the tree.
*/
314
315 memset(win32op, 0,
sizeof(win32op));
316 mm_free(win32op);
317 }
你真的懂select吗？？
关注
打赏
