lighttpd学习笔记二

记录一下lighttpd的事件处理机制，这个基本上就是和libevent差不多

lighttpd事件处理的全局数据结构主要有

typedef struct fdevents {
	fdevent_handler_t type;   //事件处理类型，lighttpd通过配置文件获取
	fdnode **fdarray;         //回调事件，参数等保存在这个结构中   
	size_t maxfds;
#ifdef USE_LINUX_EPOLL
	int epoll_fd;
	struct epoll_event *epoll_events;
#endif
#ifdef USE_SELECT
	fd_set select_read;
	fd_set select_write;
	fd_set select_error;

	fd_set select_set_read;
	fd_set select_set_write;
	fd_set select_set_error;

	int select_max_fd;
#endif
	int (*reset)(struct fdevents *ev);
	void (*free)(struct fdevents *ev);

	int (*event_add)(struct fdevents *ev, int fde_ndx, int fd, int events);
	int (*event_del)(struct fdevents *ev, int fde_ndx, int fd);
	int (*event_get_revent)(struct fdevents *ev, size_t ndx);
	int (*event_get_fd)(struct fdevents *ev, size_t ndx);

	int (*event_next_fdndx)(struct fdevents *ev, int ndx);

	int (*poll)(struct fdevents *ev, int timeout_ms);

	int (*fcntl_set)(struct fdevents *ev, int fd);
} fdevents;

我只熟悉epoll和select，所以把其他平台的都去掉了，函数指针实际是虚函数，这种方式已经很熟悉了

typedef struct _fdnode {
	fdevent_handler handler;
	void *ctx;
	int fd;

	struct _fdnode *prev, *next;
} fdnode;

fdnode的结构就是保存回调事件及参数的，这个实际是以fd为下标的，保证以O(1)性能查找指定fd对应的回调函数

使用这个事件处理器的外部暴露函数是

fdevents *fdevent_init(size_t maxfds, fdevent_handler_t type);
int fdevent_reset(fdevents *ev);
void fdevent_free(fdevents *ev);

int fdevent_event_add(fdevents *ev, int *fde_ndx, int fd, int events);
int fdevent_event_del(fdevents *ev, int *fde_ndx, int fd);
int fdevent_event_get_revent(fdevents *ev, size_t ndx);
int fdevent_event_get_fd(fdevents *ev, size_t ndx);
fdevent_handler fdevent_get_handler(fdevents *ev, int fd);
void * fdevent_get_context(fdevents *ev, int fd);

int fdevent_event_next_fdndx(fdevents *ev, int ndx);

int fdevent_poll(fdevents *ev, int timeout_ms);

int fdevent_register(fdevents *ev, int fd, fdevent_handler handler, void *ctx);
int fdevent_unregister(fdevents *ev, int fd);

int fdevent_fcntl_set(fdevents *ev, int fd);

这些函数位于fdevent.c中，另外还有

int fdevent_select_init(fdevents *ev);
int fdevent_poll_init(fdevents *ev);
int fdevent_linux_rtsig_init(fdevents *ev);
int fdevent_linux_sysepoll_init(fdevents *ev);
int fdevent_solaris_devpoll_init(fdevents *ev);
int fdevent_freebsd_kqueue_init(fdevents *ev);

这些函数位于具体的实现中，比如 int fdevent_linux_sysepoll_init(fdevents *ev);在
fdevent_linux_sysepoll.c 文件中定义
int fdevent_select_init(fdevents *ev);在
fdevent_select.c中

也就是说处理器的初始化工作是交给具体的实现完成的，流程是首先调用fdevent.c中的fdevent_init

fdevents *fdevent_init(size_t maxfds, fdevent_handler_t type) {
        fdevents *ev;

	ev = calloc(1, sizeof(*ev));
	ev->fdarray = calloc(maxfds, sizeof(*ev->fdarray));
	ev->maxfds = maxfds;

	switch(type) {
	case FDEVENT_HANDLER_SELECT:
		if (0 != fdevent_select_init(ev)) {
			fprintf(stderr, "%s.%d: event-handler select failed\n",
				__FILE__, __LINE__);
			return NULL;
		}
		break;
	case FDEVENT_HANDLER_LINUX_SYSEPOLL:
		if (0 != fdevent_linux_sysepoll_init(ev)) {
			fprintf(stderr, "%s.%d: event-handler linux-sysepoll failed, try to set server.event-handler = \"poll\" or \"select\"\n",
				__FILE__, __LINE__);
			return NULL;
		}
		break;
	return ev;
}

fdevent_init只初始化了全局fdevents结构，然后就跳到具体的实现中，比如fdevent_linux_sysepoll_init

int fdevent_linux_sysepoll_init(fdevents *ev) {
	ev->type = FDEVENT_HANDLER_LINUX_SYSEPOLL;
#define SET(x) \
	ev->x = fdevent_linux_sysepoll_##x;

	SET(free);
	SET(poll);

	SET(event_del);
	SET(event_add);

	SET(event_next_fdndx);
	SET(event_get_fd);
	SET(event_get_revent);

	if (-1 == (ev->epoll_fd = epoll_create(ev->maxfds))) {
		fprintf(stderr, "%s.%d: epoll_create failed (%s), try to set server.event-handler = \"poll\" or \"select\"\n",
			__FILE__, __LINE__, strerror(errno));

		return -1;
	}

	if (-1 == fcntl(ev->epoll_fd, F_SETFD, FD_CLOEXEC)) {
		fprintf(stderr, "%s.%d: epoll_create failed (%s), try to set server.event-handler = \"poll\" or \"select\"\n",
			__FILE__, __LINE__, strerror(errno));

		close(ev->epoll_fd);

		return -1;
	}

	ev->epoll_events = malloc(ev->maxfds * sizeof(*ev->epoll_events));

	return 0;
}

这个函数的功能包括2点
1.初始化全局fdevents中的函数指针，即绑定虚函数具体的实现
2.初始化具体实现所需的数据结构，比如epoll 的 struct epoll_event 等

最后看下处理器处理事件的过程

if ((n = fdevent_poll(srv->ev, 1000)) > 0) {
			/* n is the number of events */
			int revents;
			int fd_ndx;
			fd_ndx = -1;
			do {
				fdevent_handler handler;
				void *context;
				handler_t r;

				fd_ndx  = fdevent_event_next_fdndx (srv->ev, fd_ndx);
				revents = fdevent_event_get_revent (srv->ev, fd_ndx);
				fd      = fdevent_event_get_fd     (srv->ev, fd_ndx);
				handler = fdevent_get_handler(srv->ev, fd);
				context = fdevent_get_context(srv->ev, fd);

				/* connection_handle_fdevent needs a joblist_append */
#if 0
				log_error_write(srv, __FILE__, __LINE__, "sdd",
						"event for", fd, revents);
#endif
				switch (r = (*handler)(srv, context, revents)) {
				    //处理结果 case 省略
				}
			} while (--n > 0);
		}

fdevent_poll 很容易想到就是 epoll_wait 或者 select 的阻塞调用
后面的do while循环就是当返回大于 0时，处理所有事件，由于epoll和select 不同，该处理器通过

fd_ndx  = fdevent_event_next_fdndx (srv->ev, fd_ndx);
revents = fdevent_event_get_revent (srv->ev, fd_ndx);
fd      = fdevent_event_get_fd     (srv->ev, fd_ndx);

三个函数提供统一行为

for epoll 调用

static int fdevent_linux_sysepoll_event_next_fdndx(fdevents *ev, int ndx) {
	size_t i;

	UNUSED(ev);

	i = (ndx < 0) ? 0 : ndx + 1;

	return i;
}

其实这个fd_ndx就是从 0~n 的序列，因为epoll已经将可处理的事件集合放入了struct epoll_event结构体集合里了

for select

static int fdevent_select_event_next_fdndx(fdevents *ev, int ndx) {
	int i;

	i = (ndx < 0) ? 0 : ndx + 1;

	for (; i < ev->select_max_fd + 1; i++) {
		if (FD_ISSET(i, &(ev->select_read))) break;
		if (FD_ISSET(i, &(ev->select_write))) break;
		if (FD_ISSET(i, &(ev->select_error))) break;
	}

	return i;
}

select 比较麻烦，因为不像epoll那样已经将所有可处理的fd返回，select 需要从 0开始依次FD_ISSET来判断是否是可处理事件，下次继续从当前的这个ndx开始，其实这个ndx也就是fd了