libevent几个结构体的理解

怼烎@ 2023-07-03 10:59 7阅读 0赞

struct event base

struct event_base { 
    	const struct eventop *evsel;
    	void *evbase;//poolop pointer
    	int event_count;		/* counts number of total events */
    	int event_count_active;	/* counts number of active events */
    
    	int event_gotterm;		/* Set to terminate loop */
    	int event_break;		/* Set to terminate loop immediately */
    
    	/* active event management */
    	struct event_list **activequeues;//数组,好几个事件优先级一样，所以用队列
    	int nactivequeues;//队列的大小
    
    	/* signal handling info */
    	struct evsignal_info sig;
    
    	struct event_list eventqueue;//这个是个双向队列的头队列
    	struct timeval event_tv;
    
    	struct min_heap timeheap;//定时器小根堆
    
    	struct timeval tv_cache;//时间缓存
    };

这里要注意struct event\_list \*\*activequeues;为什么用双指针，这是因为很多事件的优先级一致，所以用队列数组来存放，这样导致有些事件不能第一时间处理

struct event { 
    	TAILQ_ENTRY (event) ev_next;//I/O
    	TAILQ_ENTRY (event) ev_active_next;
    	TAILQ_ENTRY (event) ev_signal_next;//TIMEOUT
    	unsigned int min_heap_idx;	/* for managing timeouts */
    
    	struct event_base *ev_base;
    
    	int ev_fd;
    	short ev_events;
    	short ev_ncalls;//事件触发后调用的次数
    	short *ev_pncalls;	/* Allows deletes in callback */
    
    	struct timeval ev_timeout;
    
    	int ev_pri;		/* smaller numbers are higher priority */
    
    	void (*ev_callback)(int, short, void *arg);
    	void *ev_arg;//回调函数的参数
    
    	int ev_res;		/* result passed to event callback */
    	int ev_flags;  /*state */
    };

这里主要理解几个  
TAILQ\_ENTRY  
因为一个event可能在  
struct event\_list eventqueue;//这个是个双向队列的头队列  
这个队列里面，也有可能在struct event\_list \*\*activequeues;队列里面

struct pollop { 
    	int event_count;		/* Highest number alloc event_set容量*/
    	int nfds;                       /* Size of event_* 实际个数*/
    	int fd_count;                   /* Size of idxplus1_by_fd */
    	struct pollfd *event_set;//这三个数组是一一对应的，f对于cb
    	struct event **event_r_back;
    	struct event **event_w_back;
    	int *idxplus1_by_fd; /* Index into event_set by fd; we add 1 so * that 0 (which is easy to memset) can mean * "no entry." 比如，fd=127,那么就把fd放在idxplus1_by_fd[127 ],且fd+1*/
    				  //idxplus1_by_fd[ev_fd]这里面以具体文件描述符作为下标，里面存放pfd在struct pollfd *event_set中的下表
    };

这个结构体比较重要的就是int \*idxplus1\_by\_fd这个，仔细看看它的空间内存分配方式

if (ev->ev_fd >= pop->fd_count) { //因为后者是根据前者的ev_fd作为下标来存放fd+1的
    		int *tmp_idxplus1_by_fd;
    		int new_count;
    		if (pop->fd_count < 32)
    			new_count = 32;
    		else
    			new_count = pop->fd_count * 2;
    		while (new_count <= ev->ev_fd)//注意这里，这个数组，fd对应的位置写入该fd+1
    			new_count *= 2;
    		tmp_idxplus1_by_fd =
    			realloc(pop->idxplus1_by_fd, new_count * sizeof(int));
    		if (tmp_idxplus1_by_fd == NULL) { 
    			event_warn("realloc");
    			return (-1);
    		}
    		pop->idxplus1_by_fd = tmp_idxplus1_by_fd;
    		memset(pop->idxplus1_by_fd + pop->fd_count,
    		       0, sizeof(int)*(new_count - pop->fd_count));
    		pop->fd_count = new_count;
    	}