Squid Epoll网络模型

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Squid Epoll网络模型

Squid 历经2.x, 3.x，官网已经有正在开发中的4.0版本。
Squid如今以20万行风骚代码让码农们找不着北了，本文就以Squid-4.0.0的源码为例吐槽一下。
Squid编译时可以根据OS自动选择支持的网络模型，对网络的支持最终会编译到ModEpoll.cc、
ModKqueue.cc、ModPoll.cc、ModSelect.cc。这些文件针对不同网络都有实现，
最终导出几个公共函数SelectLoopInit、SetSelect、ResetSelect、DoSelect。

　　风骚的SetSelect

SetSelect(int fd, unsigned int type, PF * handler, void *client_data, time_t timeout)
// If read is an interest
if (type & COMM_SELECT_READ) {
if (handler) {
// Hack to keep the events flowing if there is data immediately ready
if (F->flags.read_pending)
ev.events |= EPOLLOUT;
ev.events |= EPOLLIN;
}
F->read_handler = handler;
F->read_data = client_data;
// Otherwise, use previously stored value
} else if (F->epoll_state & EPOLLIN) {
ev.events |= EPOLLIN;
}
// If write is an interest
if (type & COMM_SELECT_WRITE) {
if (handler)
ev.events |= EPOLLOUT;
F->write_handler = handler;
F->write_data = client_data;
// Otherwise, use previously stored value
} else if (F->epoll_state & EPOLLOUT) {
ev.events |= EPOLLOUT;
}
if (ev.events)
ev.events |= EPOLLHUP | EPOLLERR;
if (ev.events != F->epoll_state) {
if (F->epoll_state) // already monitoring something.
epoll_ctl_type = ev.events ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;
else
epoll_ctl_type = EPOLL_CTL_ADD;
F->epoll_state = ev.events;
根据SetSelect设置的读写类型Read或者Write保留其它事件不变，
从而达到每次只改变需要设置的事件回调。最终根据ev.events的值判断
是否需要Mod或者Del。

　　吊的不行的DoSelect

        if (cevents->events & (EPOLLIN|EPOLLHUP|EPOLLERR) || F->flags.read_pending) {
if ((hdl = F->read_handler) != NULL) {
debugs(5, DEBUG_EPOLL ? 0 : 8, HERE << "Calling read handler on FD " << fd);
PROF_start(comm_write_handler);
F->flags.read_pending = 0;
F->read_handler = NULL;
hdl(fd, F->read_data);
PROF_stop(comm_write_handler);
++ statCounter.select_fds;
} else {
debugs(5, DEBUG_EPOLL ? 0 : 8, HERE << "no read handler for FD " << fd);
// remove interest since no handler exist for this event.
SetSelect(fd, COMM_SELECT_READ, NULL, NULL, 0);
}
}
if (cevents->events & (EPOLLOUT|EPOLLHUP|EPOLLERR)) {
if ((hdl = F->write_handler) != NULL) {
debugs(5, DEBUG_EPOLL ? 0 : 8, HERE << "Calling write handler on FD " << fd);
PROF_start(comm_read_handler);
F->write_handler = NULL;
hdl(fd, F->write_data);
PROF_stop(comm_read_handler);
++ statCounter.select_fds;
} else {
debugs(5, DEBUG_EPOLL ? 0 : 8, HERE << "no write handler for FD " << fd);
// remove interest since no handler exist for this event.
SetSelect(fd, COMM_SELECT_WRITE, NULL, NULL, 0);
}
}
每次执行完回调后handler = NULL，epoll在该套接字下一次事件中
SetSelect(fd, COMM_SELECT_WRITE, NULL, NULL, 0)将该套接字删除，
所以如果还想继续监听套接字事件必需在回调函数中手动执行SetSelect。

　　提取的Epoll模型
感受到Squid的如此强大，不由自主的提取了框架并做了一个小Demo。
顺便献上git地址https://github.com/strong46066999/epoll。

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