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Update Socket.md
重新绘制 I/O 模型的配图，更新非阻塞 I/O 和 select 示例的描述。
This commit is contained in:
CyC2018
+31
-20
@@ -48,15 +48,15 @@ Unix 有五种 I/O 模型：
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ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen);
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```
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492928416812_4.png"/> </div><br>
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<div align="center"> <img src="pics/io-blocking.png" width="760px"/> </div><br>
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### 非阻塞式 I/O
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应用进程执行系统调用之后，内核返回一个错误码。应用进程可以继续执行，但是需要不断的执行系统调用来获知 I/O 是否完成，这种方式称为轮询（polling）。
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应用进程执行系统调用之后，如果数据还没有准备好，内核立即返回错误码 EAGAIN（也写作 EWOULDBLOCK）。应用进程可以继续执行，但是需要不断的执行系统调用来获知 I/O 是否完成，这种方式称为轮询（polling）。
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由于 CPU 要处理更多的系统调用，因此这种模型的 CPU 利用率比较低。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492929000361_5.png"/> </div><br>
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<div align="center"> <img src="pics/io-nonblocking.png" width="760px"/> </div><br>
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### I/O 复用
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@@ -66,7 +66,7 @@ ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *
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如果一个 Web 服务器没有 I/O 复用，那么每一个 Socket 连接都需要创建一个线程去处理。如果同时有几万个连接，那么就需要创建相同数量的线程。相比于多进程和多线程技术，I/O 复用不需要进程线程创建和切换的开销，系统开销更小。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492929444818_6.png"/> </div><br>
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<div align="center"> <img src="pics/io-multiplex.png" width="760px"/> </div><br>
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### 信号驱动 I/O
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@@ -74,7 +74,7 @@ ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *
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相比于非阻塞式 I/O 的轮询方式，信号驱动 I/O 的 CPU 利用率更高。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492929553651_7.png"/> </div><br>
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<div align="center"> <img src="pics/io-signal.png" width="760px"/> </div><br>
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### 异步 I/O
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@@ -82,7 +82,7 @@ ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *
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异步 I/O 与信号驱动 I/O 的区别在于，异步 I/O 的信号是通知应用进程 I/O 完成，而信号驱动 I/O 的信号是通知应用进程可以开始 I/O。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492930243286_8.png"/> </div><br>
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<div align="center"> <img src="pics/io-async.png" width="760px"/> </div><br>
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### 五大 I/O 模型比较
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@@ -93,7 +93,7 @@ ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *
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非阻塞式 I/O 、信号驱动 I/O 和异步 I/O 在第一阶段不会阻塞。
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/1492928105791_3.png"/> </div><br>
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<div align="center"> <img src="pics/io-compare.png" width="760px"/> </div><br>
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## 二、I/O 复用
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@@ -138,17 +138,21 @@ tv.tv_usec = 0;
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int ret = select( largest_sock + 1, &fd_in, &fd_out, NULL, &tv );
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// Check if select actually succeed
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if ( ret == -1 )
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if ( ret == -1 ) {
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// report error and abort
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else if ( ret == 0 )
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}
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else if ( ret == 0 ) {
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// timeout; no event detected
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}
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else
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{
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if ( FD_ISSET( sock1, &fd_in ) )
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if ( FD_ISSET( sock1, &fd_in ) ) {
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// input event on sock1
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}
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if ( FD_ISSET( sock2, &fd_out ) )
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if ( FD_ISSET( sock2, &fd_out ) ) {
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// output event on sock2
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}
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}
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```
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@@ -184,12 +188,14 @@ fds[1].fd = sock2;
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fds[1].events = POLLOUT;
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// Wait 10 seconds
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int ret = poll( &fds, 2, 10000 );
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int ret = poll( fds, 2, 10000 );
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// Check if poll actually succeed
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if ( ret == -1 )
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if ( ret == -1 ) {
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// report error and abort
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else if ( ret == 0 )
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}
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else if ( ret == 0 ) {
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// timeout; no event detected
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}
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else
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{
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// If we detect the event, zero it out so we can reuse the structure
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@@ -234,7 +240,7 @@ epoll_ctl() 用于向内核注册新的描述符或者是改变某个文件描
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从上面的描述可以看出，epoll 只需要将描述符从进程缓冲区向内核缓冲区拷贝一次，并且进程不需要通过轮询来获得事件完成的描述符。
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<div align="center"> <img src="pics/epoll.png" width="600px"/> </div><br>
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<div align="center"> <img src="pics/epoll.png" width="640px"/> </div><br>
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epoll 仅适用于 Linux OS。
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@@ -247,8 +253,9 @@ epoll 对多线程编程更加友好，一个线程调用了 epoll_wait() 另一
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// The function argument is ignored (it was not before, but now it is), so put your favorite number here
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int pollingfd = epoll_create( 0xCAFE );
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if ( pollingfd < 0 )
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// report error
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if ( pollingfd < 0 ) {
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// report error
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}
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// Initialize the epoll structure in case more members are added in future
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struct epoll_event ev = { 0 };
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@@ -261,8 +268,9 @@ ev.data.ptr = pConnection1;
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ev.events = EPOLLIN | EPOLLONESHOT;
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// Add the descriptor into the monitoring list. We can do it even if another thread is
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// waiting in epoll_wait - the descriptor will be properly added
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if ( epoll_ctl( epollfd, EPOLL_CTL_ADD, pConnection1->getSocket(), &ev ) != 0 )
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if ( epoll_ctl( pollingfd, EPOLL_CTL_ADD, pConnection1->getSocket(), &ev ) != 0 ) {
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// report error
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}
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// Wait for up to 20 events (assuming we have added maybe 200 sockets before that it may happen)
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struct epoll_event pevents[ 20 ];
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@@ -270,10 +278,12 @@ struct epoll_event pevents[ 20 ];
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// Wait for 10 seconds, and retrieve less than 20 epoll_event and store them into epoll_event array
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int ready = epoll_wait( pollingfd, pevents, 20, 10000 );
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// Check if epoll actually succeed
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if ( ret == -1 )
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if ( ready == -1 ) {
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// report error and abort
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else if ( ret == 0 )
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}
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else if ( ready == 0 ) {
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// timeout; no event detected
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}
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else
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{
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// Check if any events detected
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@@ -337,3 +347,4 @@ poll 没有最大描述符数量的限制，如果平台支持并且对实时性
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- [poll vs select vs event-based](https://daniel.haxx.se/docs/poll-vs-select.html)
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- [select / poll / epoll: practical difference for system architects](http://www.ulduzsoft.com/2014/01/select-poll-epoll-practical-difference-for-system-architects/)
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- [Browse the source code of userspace/glibc/sysdeps/unix/sysv/linux/ online](https://code.woboq.org/userspace/glibc/sysdeps/unix/sysv/linux/)
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- [epoll(7) — Linux manual page](https://man7.org/linux/man-pages/man7/epoll.7.html)
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<rect width="100%" height="100%" fill="#FFFFFF"/>
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<text x="380" y="28" class="title">异步 I/O</text>
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<rect x="120" y="46" width="160" height="30" rx="6" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="200" y="65.5" class="c sub b">应用进程</text>
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<rect x="460" y="46" width="160" height="30" rx="6" fill="#C6E4FB" stroke="#7FB2D6"/>
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<text x="540" y="65.5" class="c sub b">内核</text>
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<text x="590" y="139" class="sub b" style="fill:#444">① 等待数据</text>
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<text x="590" y="155" class="sub">例如等对方发来 hello</text>
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<rect x="554" y="244" width="26" height="46" rx="3" fill="#E6E3FA" stroke="#B8B0DE" stroke-width="1"/>
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<text x="590" y="270" class="sub b" style="fill:#444">② 复制到用户缓冲区</text>
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<text x="554" y="214" class="sub">数据到达</text>
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||||
<line x1="200" y1="100" x2="540" y2="100" class="arrow "/>
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<text x="370" y="95" class="c sub mono" style="fill:#444">aio_read(fd, buf, 1024)</text>
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<line x1="540" y1="114" x2="200" y2="114" class="arrow dash"/>
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||||
<text x="370" y="109" class="c sub" style="fill:#444">立即返回</text>
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<rect x="193" y="118" width="14" height="172" rx="3" fill="#C6ECE9" stroke="#7DBCB7"/>
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||||
<text x="186" y="208" class="sub ok e">继续执行其它代码</text>
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<line x1="540" y1="290" x2="200" y2="290" class="arrow dash"/>
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<text x="370" y="285" class="c sub" style="fill:#444">完成通知：buf 中已经是 hello</text>
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<text x="30" y="356" class="sub">两个阶段都由内核完成，进程收到通知时数据已经在自己的缓冲区中。Linux 上实际的异步 I/O 多用 io_uring。</text>
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<text x="590" y="139" class="sub b" style="fill:#444">① 等待数据</text>
|
||||
<text x="590" y="155" class="sub">例如等对方发来 hello</text>
|
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|
||||
<text x="554" y="214" class="sub">数据到达</text>
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<text x="186" y="200" class="sub note e">两个阶段都阻塞</text>
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|
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<text x="370" y="285" class="c sub" style="fill:#444">返回 5（读到 hello）</text>
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||||
<text x="30" y="356" class="sub">本机测试：对方 300 ms 后才发送，recv 阻塞 0.31 秒后返回。等待期间线程不占用 CPU，但也不能做别的事。</text>
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<text x="380" y="28" class="title">五种 I/O 模型的比较</text>
|
||||
<text x="108" y="129" class="sub b e" style="fill:#444">① 等待数据</text>
|
||||
<text x="108" y="224" class="sub b e" style="fill:#444">② 复制数据</text>
|
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<text x="180" y="58" class="c b" style="fill:#444">阻塞式</text>
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<text x="194" y="129" class="sub">阻塞</text>
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<text x="194" y="224" class="sub">阻塞</text>
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<text x="300" y="58" class="c b" style="fill:#444">非阻塞式</text>
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<text x="314" y="224" class="sub">阻塞</text>
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<text x="420" y="58" class="c b" style="fill:#444">I/O 复用</text>
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<rect x="412.0" y="76" width="16" height="98" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
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<text x="434" y="129" class="sub">阻塞在 select</text>
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<rect x="412.0" y="186" width="16" height="68" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
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<text x="434" y="224" class="sub">阻塞</text>
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<text x="540" y="58" class="c b" style="fill:#444">信号驱动</text>
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<rect x="532.0" y="76" width="16" height="98" rx="3" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="554" y="224" class="sub">阻塞</text>
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<text x="660" y="58" class="c b" style="fill:#444">异步</text>
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<rect x="652.0" y="76" width="16" height="98" rx="3" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="674" y="224" class="sub">不阻塞</text>
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<path d="M126,272 q0,8 8,8 H592 q8,0 8,-8" class="line"/>
|
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<text x="360" y="296" class="c sub">同步 I/O：第二阶段由进程自己 recvfrom，都会阻塞</text>
|
||||
<text x="660" y="296" class="c sub">异步 I/O</text>
|
||||
<text x="30" y="320" class="sub">红色表示进程阻塞，浅青色表示进程可以做别的事。前四种的区别只在第一阶段。</text>
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</svg>
|
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|
After Width: | Height: | Size: 4.0 KiB |
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<svg xmlns="http://www.w3.org/2000/svg" width="760" height="380" viewBox="0 0 760 380">
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<style>
|
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text { font-family: "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; fill: #3F3F3F; font-size: 12px; }
|
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.title { font-weight: bold; font-size: 15px; fill: #333; text-anchor: middle; }
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.b { font-weight: bold; }
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.c { text-anchor: middle; }
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.e { text-anchor: end; }
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.sub { font-size: 11px; fill: #6E6E6E; }
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.note { fill: #C0605A; }
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.ok { fill: #6A9F68; }
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.mono { font-family: Menlo, Consolas, monospace; }
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.arrow { stroke: #555; stroke-width: 1.1; fill: none; marker-end: url(#a); }
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.red { stroke: #C0605A; marker-end: url(#r); }
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.green { stroke: #6A9F68; marker-end: url(#g); }
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.dash { stroke-dasharray: 5 4; }
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.line { stroke: #555; stroke-width: 1.1; fill: none; }
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.frame { fill: none; stroke: #999; stroke-width: 1; stroke-dasharray: 4 3; }
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.shadow { fill: #DADADA; }
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</style>
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<marker id="a" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#555"/>
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</marker>
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<marker id="r" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#C0605A"/>
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</marker>
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<marker id="g" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<rect width="100%" height="100%" fill="#FFFFFF"/>
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<text x="380" y="28" class="title">I/O 复用</text>
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<rect x="120" y="46" width="160" height="30" rx="6" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="200" y="65.5" class="c sub b">应用进程</text>
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<rect x="460" y="46" width="160" height="30" rx="6" fill="#C6E4FB" stroke="#7FB2D6"/>
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<text x="540" y="65.5" class="c sub b">内核</text>
|
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<line x1="200" y1="78" x2="200" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
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<line x1="540" y1="78" x2="540" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
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<rect x="554" y="96" width="26" height="94" rx="3" fill="#EAE9E7" stroke="#BFBEBA" stroke-width="1"/>
|
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<text x="590" y="139" class="sub b" style="fill:#444">① 等待数据</text>
|
||||
<text x="590" y="155" class="sub">例如等对方发来 hello</text>
|
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<rect x="554" y="244" width="26" height="46" rx="3" fill="#E6E3FA" stroke="#B8B0DE" stroke-width="1"/>
|
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<text x="590" y="270" class="sub b" style="fill:#444">② 复制到用户缓冲区</text>
|
||||
<text x="554" y="214" class="sub">数据到达</text>
|
||||
<line x1="200" y1="100" x2="540" y2="100" class="arrow "/>
|
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<text x="370" y="95" class="c sub mono" style="fill:#444">select([fd1, fd2, …])</text>
|
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<rect x="193" y="102" width="14" height="88" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
|
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<text x="186" y="150" class="sub note e">阻塞在 select</text>
|
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<line x1="540" y1="190" x2="200" y2="190" class="arrow dash"/>
|
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<text x="370" y="185" class="c sub" style="fill:#444">fd1 可读</text>
|
||||
<line x1="200" y1="244" x2="540" y2="244" class="arrow "/>
|
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<text x="370" y="239" class="c sub mono" style="fill:#444">recvfrom(fd1)</text>
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<rect x="193" y="246" width="14" height="44" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
|
||||
<text x="186" y="272" class="sub note e">复制时阻塞</text>
|
||||
<line x1="540" y1="290" x2="200" y2="290" class="arrow dash"/>
|
||||
<text x="370" y="285" class="c sub" style="fill:#444">返回 5</text>
|
||||
<text x="30" y="356" class="sub">和阻塞式 I/O 一样要等，但一次可以等很多个连接，任何一个就绪就返回，一个线程就能处理大量连接。</text>
|
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</svg>
|
||||
|
After Width: | Height: | Size: 3.6 KiB |
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|
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<svg xmlns="http://www.w3.org/2000/svg" width="760" height="380" viewBox="0 0 760 380">
|
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<style>
|
||||
text { font-family: "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; fill: #3F3F3F; font-size: 12px; }
|
||||
.title { font-weight: bold; font-size: 15px; fill: #333; text-anchor: middle; }
|
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.b { font-weight: bold; }
|
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.c { text-anchor: middle; }
|
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.e { text-anchor: end; }
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.sub { font-size: 11px; fill: #6E6E6E; }
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.note { fill: #C0605A; }
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.ok { fill: #6A9F68; }
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.mono { font-family: Menlo, Consolas, monospace; }
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.arrow { stroke: #555; stroke-width: 1.1; fill: none; marker-end: url(#a); }
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.red { stroke: #C0605A; marker-end: url(#r); }
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.green { stroke: #6A9F68; marker-end: url(#g); }
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.dash { stroke-dasharray: 5 4; }
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.line { stroke: #555; stroke-width: 1.1; fill: none; }
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.frame { fill: none; stroke: #999; stroke-width: 1; stroke-dasharray: 4 3; }
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.shadow { fill: #DADADA; }
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</style>
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<defs>
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<marker id="a" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#555"/>
|
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</marker>
|
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<marker id="r" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#C0605A"/>
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</marker>
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<marker id="g" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#6A9F68"/>
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<rect width="100%" height="100%" fill="#FFFFFF"/>
|
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|
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<text x="380" y="28" class="title">非阻塞式 I/O</text>
|
||||
<rect x="120" y="46" width="160" height="30" rx="6" fill="#C6ECE9" stroke="#7DBCB7"/>
|
||||
<text x="200" y="65.5" class="c sub b">应用进程</text>
|
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<rect x="460" y="46" width="160" height="30" rx="6" fill="#C6E4FB" stroke="#7FB2D6"/>
|
||||
<text x="540" y="65.5" class="c sub b">内核</text>
|
||||
<line x1="200" y1="78" x2="200" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
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<line x1="540" y1="78" x2="540" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
|
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<rect x="554" y="96" width="26" height="94" rx="3" fill="#EAE9E7" stroke="#BFBEBA" stroke-width="1"/>
|
||||
<text x="590" y="139" class="sub b" style="fill:#444">① 等待数据</text>
|
||||
<text x="590" y="155" class="sub">例如等对方发来 hello</text>
|
||||
<rect x="554" y="244" width="26" height="46" rx="3" fill="#E6E3FA" stroke="#B8B0DE" stroke-width="1"/>
|
||||
<text x="590" y="270" class="sub b" style="fill:#444">② 复制到用户缓冲区</text>
|
||||
<text x="554" y="214" class="sub">数据到达</text>
|
||||
<line x1="200" y1="96" x2="540" y2="96" class="arrow "/>
|
||||
<text x="370" y="91" class="c sub mono" style="fill:#444">recvfrom</text>
|
||||
<line x1="540" y1="110" x2="200" y2="110" class="arrow dash"/>
|
||||
<text x="370" y="124" class="c sub" style="fill:#444">EAGAIN（没有数据）</text>
|
||||
<line x1="200" y1="150" x2="540" y2="150" class="arrow "/>
|
||||
<text x="370" y="145" class="c sub mono" style="fill:#444">recvfrom</text>
|
||||
<line x1="540" y1="164" x2="200" y2="164" class="arrow dash"/>
|
||||
<text x="370" y="178" class="c sub" style="fill:#444">EAGAIN ……共 6 次</text>
|
||||
<line x1="200" y1="206" x2="540" y2="206" class="arrow "/>
|
||||
<text x="370" y="201" class="c sub mono" style="fill:#444">recvfrom</text>
|
||||
<rect x="193" y="100" width="14" height="100" rx="3" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="186" y="154" class="sub ok e">轮询</text>
|
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<rect x="193" y="208" width="14" height="82" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
|
||||
<text x="186" y="253" class="sub note e">复制时阻塞</text>
|
||||
<line x1="540" y1="290" x2="200" y2="290" class="arrow dash"/>
|
||||
<text x="370" y="285" class="c sub" style="fill:#444">返回 5</text>
|
||||
<text x="30" y="356" class="sub">本机测试：每 50 ms 调用一次 recv，前 6 次返回 EAGAIN（没有数据），第 7 次读到 hello。轮询本身要消耗 CPU。</text>
|
||||
</svg>
|
||||
|
After Width: | Height: | Size: 3.9 KiB |
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|
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<svg xmlns="http://www.w3.org/2000/svg" width="760" height="380" viewBox="0 0 760 380">
|
||||
<style>
|
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text { font-family: "PingFang SC", "Microsoft YaHei", Helvetica, Arial, sans-serif; fill: #3F3F3F; font-size: 12px; }
|
||||
.title { font-weight: bold; font-size: 15px; fill: #333; text-anchor: middle; }
|
||||
.b { font-weight: bold; }
|
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.c { text-anchor: middle; }
|
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.e { text-anchor: end; }
|
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.sub { font-size: 11px; fill: #6E6E6E; }
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.note { fill: #C0605A; }
|
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.ok { fill: #6A9F68; }
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.mono { font-family: Menlo, Consolas, monospace; }
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.arrow { stroke: #555; stroke-width: 1.1; fill: none; marker-end: url(#a); }
|
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.red { stroke: #C0605A; marker-end: url(#r); }
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.green { stroke: #6A9F68; marker-end: url(#g); }
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.dash { stroke-dasharray: 5 4; }
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.line { stroke: #555; stroke-width: 1.1; fill: none; }
|
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.frame { fill: none; stroke: #999; stroke-width: 1; stroke-dasharray: 4 3; }
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.shadow { fill: #DADADA; }
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</style>
|
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<defs>
|
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<marker id="a" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#555"/>
|
||||
</marker>
|
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<marker id="r" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#C0605A"/>
|
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</marker>
|
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<marker id="g" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
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<path d="M1,1.5 L9.5,5 L1,8.5 z" fill="#6A9F68"/>
|
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</marker>
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</defs>
|
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<rect width="100%" height="100%" fill="#FFFFFF"/>
|
||||
|
||||
<text x="380" y="28" class="title">信号驱动 I/O</text>
|
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<rect x="120" y="46" width="160" height="30" rx="6" fill="#C6ECE9" stroke="#7DBCB7"/>
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<text x="200" y="65.5" class="c sub b">应用进程</text>
|
||||
<rect x="460" y="46" width="160" height="30" rx="6" fill="#C6E4FB" stroke="#7FB2D6"/>
|
||||
<text x="540" y="65.5" class="c sub b">内核</text>
|
||||
<line x1="200" y1="78" x2="200" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
|
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<line x1="540" y1="78" x2="540" y2="330" stroke="#BBB" stroke-dasharray="4 4"/>
|
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<rect x="554" y="96" width="26" height="94" rx="3" fill="#EAE9E7" stroke="#BFBEBA" stroke-width="1"/>
|
||||
<text x="590" y="139" class="sub b" style="fill:#444">① 等待数据</text>
|
||||
<text x="590" y="155" class="sub">例如等对方发来 hello</text>
|
||||
<rect x="554" y="244" width="26" height="46" rx="3" fill="#E6E3FA" stroke="#B8B0DE" stroke-width="1"/>
|
||||
<text x="590" y="270" class="sub b" style="fill:#444">② 复制到用户缓冲区</text>
|
||||
<text x="554" y="214" class="sub">数据到达</text>
|
||||
<line x1="200" y1="100" x2="540" y2="100" class="arrow "/>
|
||||
<text x="370" y="95" class="c sub mono" style="fill:#444">sigaction(SIGIO, handler)</text>
|
||||
<line x1="540" y1="114" x2="200" y2="114" class="arrow dash"/>
|
||||
<text x="370" y="109" class="c sub" style="fill:#444">立即返回</text>
|
||||
<rect x="193" y="118" width="14" height="72" rx="3" fill="#C6ECE9" stroke="#7DBCB7"/>
|
||||
<text x="186" y="158" class="sub ok e">继续执行其它代码</text>
|
||||
<line x1="540" y1="190" x2="200" y2="190" class="arrow dash"/>
|
||||
<text x="370" y="185" class="c sub mono" style="fill:#444">SIGIO 信号</text>
|
||||
<line x1="200" y1="244" x2="540" y2="244" class="arrow "/>
|
||||
<text x="370" y="239" class="c sub mono" style="fill:#444">在处理函数中 recvfrom</text>
|
||||
<rect x="193" y="246" width="14" height="44" rx="3" fill="#F3C6C2" stroke="#D99A94"/>
|
||||
<text x="186" y="272" class="sub note e">复制时阻塞</text>
|
||||
<line x1="540" y1="290" x2="200" y2="290" class="arrow dash"/>
|
||||
<text x="370" y="285" class="c sub" style="fill:#444">返回 5</text>
|
||||
<text x="30" y="356" class="sub">等待阶段不阻塞，数据到达时内核发信号通知“可以读了”，读取仍由进程自己完成。</text>
|
||||
</svg>
|
||||
|
After Width: | Height: | Size: 3.7 KiB |
Reference in New Issue
Block a user