memcached（二）事件模型源码分析

memcachedd事件模型

流程图

在memcached中，是先对工作者线程进行初始化并启动，然后才会创建启动主线程。

/**
* Create a socket and bind it to a specific port number
* @param interface the interface to bind to
* @param port the port number to bind to
* @param transport the transport protocol (TCP / UDP)
* @param portnumber_file A filepointer to write the port numbers to
*        when they are successfully added to the list of ports we
*        listen on.
*/
static int server_socket(const char *interface,
int port,
enum network_transport transport,
FILE *portnumber_file) {
int sfd;
struct linger ling = {0, 0};
struct addrinfo *ai;
struct addrinfo *next;
struct addrinfo hints = { .ai_flags = AI_PASSIVE,
.ai_family = AF_UNSPEC };
char port_buf[NI_MAXSERV];
int error;
int success = 0;
int flags =1;

hints.ai_socktype = IS_UDP(transport) ? SOCK_DGRAM : SOCK_STREAM;

if (port == -1) {
port = 0;
}
snprintf(port_buf, sizeof(port_buf), "%d", port);
error= getaddrinfo(interface, port_buf, &hints, &ai);
if (error != 0) {
if (error != EAI_SYSTEM)
fprintf(stderr, "getaddrinfo(): %s\n", gai_strerror(error));
else
perror("getaddrinfo()");
return 1;
}

for (next= ai; next; next= next->ai_next) {
conn *listen_conn_add;
if ((sfd = new_socket(next)) == -1) {
/* getaddrinfo can return "junk" addresses,
* we make sure at least one works before erroring.
*/
if (errno == EMFILE) {
/* ...unless we're out of fds */
perror("server_socket");
exit(EX_OSERR);
}
continue;
}

#ifdef IPV6_V6ONLY
if (next->ai_family == AF_INET6) {
error = setsockopt(sfd, IPPROTO_IPV6, IPV6_V6ONLY, (char *) &flags, sizeof(flags));
if (error != 0) {
perror("setsockopt");
close(sfd);
continue;
}
}
#endif

setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, (void *)&flags, sizeof(flags));
if (IS_UDP(transport)) {
maximize_sndbuf(sfd);
} else {
error = setsockopt(sfd, SOL_SOCKET, SO_KEEPALIVE, (void *)&flags, sizeof(flags));
if (error != 0)
perror("setsockopt");

error = setsockopt(sfd, SOL_SOCKET, SO_LINGER, (void *)&ling, sizeof(ling));
if (error != 0)
perror("setsockopt");

error = setsockopt(sfd, IPPROTO_TCP, TCP_NODELAY, (void *)&flags, sizeof(flags));
if (error != 0)
perror("setsockopt");
}

if (bind(sfd, next->ai_addr, next->ai_addrlen) == -1) {
if (errno != EADDRINUSE) {
perror("bind()");
close(sfd);
freeaddrinfo(ai);
return 1;
}
close(sfd);
continue;
} else {
success++;
if (!IS_UDP(transport) && listen(sfd, settings.backlog) == -1) {
perror("listen()");
close(sfd);
freeaddrinfo(ai);
return 1;
}
if (portnumber_file != NULL &&
(next->ai_addr->sa_family == AF_INET ||
next->ai_addr->sa_family == AF_INET6)) {
union {
struct sockaddr_in in;
struct sockaddr_in6 in6;
} my_sockaddr;
socklen_t len = sizeof(my_sockaddr);
if (getsockname(sfd, (struct sockaddr*)&my_sockaddr, &len)==0) {
if (next->ai_addr->sa_family == AF_INET) {
fprintf(portnumber_file, "%s INET: %u\n",
IS_UDP(transport) ? "UDP" : "TCP",
ntohs(my_sockaddr.in.sin_port));
} else {
fprintf(portnumber_file, "%s INET6: %u\n",
IS_UDP(transport) ? "UDP" : "TCP",
ntohs(my_sockaddr.in6.sin6_port));
}
}
}
}

if (IS_UDP(transport)) {
int c;

for (c = 0; c < settings.num_threads_per_udp; c++) {
/* Allocate one UDP file descriptor per worker thread;
* this allows "stats conns" to separately list multiple
* parallel UDP requests in progress.
*
* The dispatch code round-robins new connection requests
* among threads, so this is guaranteed to assign one
* FD to each thread.
*/
int per_thread_fd = c ? dup(sfd) : sfd;
dispatch_conn_new(per_thread_fd, conn_read,
EV_READ | EV_PERSIST,
UDP_READ_BUFFER_SIZE, transport);
}
} else {
if (!(listen_conn_add = conn_new(sfd, conn_listening,
EV_READ | EV_PERSIST, 1,
transport, main_base))) {
fprintf(stderr, "failed to create listening connection\n");
exit(EXIT_FAILURE);
}
listen_conn_add->next = listen_conn;
listen_conn = listen_conn_add;
}
}

freeaddrinfo(ai);

/* Return zero iff we detected no errors in starting up connections */
return success == 0;
}

server_socket源码

主线程事件

在主线程中通过`conn_new`函数来建立主线程和工作者线程之间的关系。

/* 设置线程事件 */
event_set(&c->event, sfd, event_flags, event_handler, (void *)c);
event_base_set(base, &c->event);
c->ev_flags = event_flags;

/* 注册事件到监听 */
if (event_add(&c->event, 0) == -1) {
perror("event_add");
return NULL;
}

事件处理

上面中设置了事件的回调函数`event_handler`，而在`event_handler`中，主要调用了`driver_machine`函数。

driver_machine看名字就知道，想发动机一样的函数，那么该函数主要是处理各种事件以及相应的处理方法。

这里只简要介绍一个函数调用`dispatch_conn_new`。

void dispatch_conn_new(int sfd, enum conn_states init_state, int event_flags,
int read_buffer_size, enum network_transport transport) {
CQ_ITEM *item = cqi_new();
char buf[1];
if (item == NULL) {
close(sfd);
/* given that malloc failed this may also fail, but let's try */
fprintf(stderr, "Failed to allocate memory for connection object\n");
return ;
}

int tid = (last_thread + 1) % settings.num_threads;

LIBEVENT_THREAD *thread = threads + tid; //循环获取工作者线程

last_thread = tid;

item->sfd = sfd;
item->init_state = init_state;
item->event_flags = event_flags;
item->read_buffer_size = read_buffer_size;
item->transport = transport;

cq_push(thread->new_conn_queue, item); //连接加入懂啊队列

memcachedD_CONN_DISPATCH(sfd, thread->thread_id);
buf[0] = 'c';
if (write(thread->notify_send_fd, buf, 1) != 1) {//向管道写入消息
perror("Writing to thread notify pipe");
}
}