epoll、select、poll的处理流程
时间: 2023-09-10 18:12:15 浏览: 95
epoll、select和poll是用于网络编程中的I/O多路复用机制,可以同时监听多个文件描述符的可读、可写或异常事件。
处理流程如下:
1. 创建监听的文件描述符集合,并将需要监听事件的文件描述符添加到集合中。
2. 调用epoll_create、select或poll函数创建一个epoll对象或描述符集。
3. 循环等待事件发生:
- epoll_wait函数:等待文件描述符集合中的事件发生,返回就绪的文件描述符列表。
- select函数:等待文件描述符集合中的事件发生,返回就绪的文件描述符列表。
- poll函数:等待文件描述符集合中的事件发生,返回就绪的文件描述符列表。
4. 遍历就绪的文件描述符列表,处理每个就绪的事件:
- 对于可读事件,读取数据并进行处理。
- 对于可写事件,写入数据。
- 对于异常事件,进行相应处理。
5. 回到步骤3继续等待事件发生。
注意:在使用这些函数时,需要注意设置超时时间和处理错误情况等。不同的函数有一些差异,但整体的处理流程是类似的。
相关问题
epoll select poll区别
回答:
epoll、select和poll是用于实现I/O多路复用的机制,它们之间有以下区别:
1. 存储方式:select和poll采用轮询的方式来检查文件描述符是否处于就绪态,而epoll采用回调机制。这意味着随着文件描述符数量的增加,select和poll的效率会线性降低,而epoll不会受到太大影响,除非活跃的socket很多。\[1\]
2. 返回就绪文件描述符:select和poll并不会明确指出是哪些文件描述符就绪,而epoll会返回就绪的文件描述符。这使得在调用select和poll后,程序需要遍历监听的整个文件描述符来找到哪些处于就绪态,而epoll则可以直接处理就绪的文件描述符。\[1\]
3. 效率:由于epoll使用回调机制和红黑树的数据结构,它的效率比select和poll更高。而select和poll需要将有关文件描述符的数据结构拷贝进内核,最后再拷贝出来,而epoll创建的有关文件描述符的数据结构本身就存于内核态中,利用mmap()文件映射内存加速与内核空间的消息传递,减少了复制开销。\[1\]\[2\]
4. 边缘触发模式:epoll支持边缘触发模式,这意味着只有在文件描述符状态发生变化时才会通知应用程序,而不是在文件描述符处于就绪态时一直通知。这可以提高效率,避免充斥大量不关心的就绪文件描述符。\[1\]
总结来说,epoll相对于select和poll具有更高的效率和更好的扩展性,特别适用于大规模并发的网络编程。而select和poll则适用于较小规模的并发处理。\[1\]\[2\]\[3\]
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C++ epoll select poll
C provides several system calls for multiplexing I/O operations, including epoll, select, and poll. These system calls allow a program to monitor multiple file descriptors (e.g. sockets or pipes) for I/O readiness, and block until at least one becomes ready.
1. epoll: epoll is a scalable I/O event notification mechanism introduced in Linux kernel version 2.6. It is considered more efficient than select and poll for large-scale applications. epoll can monitor a large number of file descriptors, and can return only those that are ready for I/O operations.
2. select: select is a system call that allows a program to monitor multiple file descriptors for I/O readiness. It is available on most Unix-like operating systems. select has some limitations, such as a maximum number of file descriptors that can be monitored and the need to iterate over all monitored file descriptors to find the ready ones.
3. poll: poll is another system call that allows a program to monitor multiple file descriptors for I/O readiness. It is similar to select, but with some differences in its interface and behavior. Like select, poll has a maximum number of file descriptors that can be monitored.
In general, epoll is considered the most efficient and scalable option for large-scale applications, while select and poll are suitable for simpler applications with fewer file descriptors. However, the choice of multiplexing mechanism depends on the specific requirements of the application.
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