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1 select function int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);1.1 parameter description the first parameter NFDs is the maximum descriptor value added to the fdset set by 1. fdset is a single-digit group with a size limit of _ fd_setsize (1024 ), each bit of the bitwise array represents whether its corresponding descriptor needs to be checked. The second, third, and fourth parameters indicate the array of file descriptor bits tha

From: http://www.cnblogs.com/aga-j/archive/2011/08/26/2153943.html Introduction to select, poll, and epoll Select In essence, select performs the next step by setting or checking the data structure that stores the FD flag. The disadvantage is:1. The number of FD monitored by a single process is limited.2. Maintain a Data Structure to store a large amount of fd data, which will cause high replication overhead when the user space and kernel

Source: http://www.cnblogs.com/sharra/archive/2010/12/30/1921287.html Because you need to understand the principle of access to the underlying device, you need to understand the Access Mechanism of Linux devices, especially when dealing with a set of non-blocking I/O, the standard term seems to be multiplexing. Some of the sentences in the following articles are quoted and the source is not pointed out in detail. Readers who have been familiar with Linux kernel or device driver development must

About I/O multiplexing:I/O multiplexing (also known as "event-driven") is the first thing to understand. The operating system provides you with a feature. When one of your sockets is readable or writable. It can give you a notice. When used with a non-clogging socket, it is only when the system notifies me which descriptive descriptor is readable that I run the read operation. The ability to ensure that every read reads valid data without making a pure return-1 and Eagain. Write operations are s

Poll Mechanism Analysis All system calls can be prefixed with "sys _" before its name, which is the corresponding function in the kernel. For example, if the system calls open, read, write, and poll, the corresponding kernel functions include sys_open, sys_read, sys_write, and sys_poll. I. kernel framework: For the system to call poll or select, the correspondin

Select, poll, and epoll are Io multiplexing mechanisms. The so-called I/O multiplexing mechanism means that multiple descriptors can be monitored through one mechanism. Once a descriptor is ready (generally read or write ), notify the program to perform corresponding read/write operations. However, select, poll, and epoll are essentially synchronous I/O, because they all need to read and write after the Rea

The select,poll,epoll is a mechanism for IO multiplexing. I/O multiplexing is a mechanism by which multiple descriptors can be monitored, and once a descriptor is ready (usually read-ready or write-ready), the program can be notified of the appropriate read and write operations. but select,poll,epoll are essentially synchronous I/O, because they all need to read and write when the read-write event is ready,

Original link: http://www.cnblogs.com/Anker/p/3265058.htmlThe select,poll,epoll is a mechanism for IO multiplexing. I/O multiplexing is a mechanism by which multiple descriptors can be monitored, and once a descriptor is ready (usually read-ready or write-ready), the program can be notified of the appropriate read and write operations. but select,poll,epoll are essentially synchronous I/O, because they all

/** * Poll Survey * * * */ Include "islogin.php"; Include ". /conn/config.inc.php "; /*action Operation initialization */ if (Emptyempty ($_request[' action ')) { $_request[' action ']= ' list '; }else { $_request[' action ']=trim ($_request[' action '); } if ($_request[' action ']== ' add ') { $tpl->assign (' Submitbutton ', ' Add '); $tpl->assign (' tmess ', ' Add voting options '); $TPL->assign (' act ', ' Insert '); $tpl->display (' Admin/addpol

1.select ModelsThe 1.1 Select function is prototyped as follows, where Nfds represents the maximum value of the Descriptor plus 1 (because this is the left-right open interval), and the middle three parameters represent a collection of different types of descriptors to listen to, timeout is used to represent the polling interval, where null means infinite wait.　　　　1.2 General steps for writing a client program using the Select function:A) initialize the parameters, including initializing the li

First, review the previous Select Select Advantages: currently supported on almost all platforms, and its good cross-platform support is one of its advantages Select Cons: 1. Each call to select () requires that the FD collection be copied from the user state to the kernel state, which is very expensive when FD is very large, and each call to select () requires the kernel to traverse all the FD that is passed in, which is also very ex

All system calls, based on the "Sys_" prefix in front of its name, are the corresponding functions in the kernel. For example, the system calls open, read, write, poll, and the corresponding kernel functions are: Sys_open, Sys_read, Sys_write, Sys_poll.First, the kernel framework:For system calls poll or select, their corresponding kernel functions are sys_poll. The pol