你真的懂select吗？？
来源：互联网 发布：姚明和邓肯比赛数据 编辑：程序博客网 时间：2024/04/27 16:36
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 < 0) 97 return (0); 98 if (--set->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 else110 ent2->write_pos_plus1 = i+1;111 }112 return (0);113 }114 115 #define NEVENT 32116 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_count137 = winop->exset_out->fd_count = 0;138 139 if (evsig_init(_base) < 0)140 winop->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 int154 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)<0)169 return (-1);170 }171 if (events & EV_WRITE) {172 if (do_fd_set(win32op, idx, fd, 0)<0)173 return (-1);174 }175 return (0);176 }177 178 int179 win32_del(struct event_base *base, evutil_socket_t fd, short old, short events,180 void *_idx)181 {182 struct win32op *win32op = base->evbase;183 struct idx_info *idx = _idx;184 185 event_debug(("%s: Removing event for "EV_SOCK_FMT,186 __func__, EV_SOCK_ARG(fd)));187 if (events & EV_READ)188 do_fd_clear(base, win32op, idx, 1);189 if (events & EV_WRITE)190 do_fd_clear(base, win32op, idx, 0);191 192 return 0;193 }194 195 static void196 fd_set_copy(struct win_fd_set *out, const struct win_fd_set *in)197 {198 out->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;i<s->fd_count;++i)208 printf("%d ",(int)s->fd_array[i]);209 printf("]\n");210 }211 */212 213 int214 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 < 0)245 msec = LONG_MAX;246 /* Windows doesn't like you to call select() with no sockets */247 Sleep(msec);248 return (0);249 }250 251 EVBASE_RELEASE_LOCK(base, th_base_lock);252 253 res = select(fd_count,254 (struct fd_set*)win32op->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 <= 0) {263 return res;264 }265 266 if (win32op->readset_out->fd_count) {267 i = rand() % win32op->readset_out->fd_count;268 for (j=0; j<win32op->readset_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; j<win32op->exset_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; j<win32op->writeset_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 void298 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 } 0 0
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