poll code

up the process waiting for sleep in the queue. If a certain timeout value is exceeded (specified by schedule_timeout) and no one wakes up, the process that calls the SELECT statement will be wakened again to obtain the CPU, traverse the FD again, and determine whether the FD is ready. 8. Copy fd_set from the kernel space to the user space. Summary: Disadvantages of select: (1) Each time you call the SELECT statement, you need to copy the FD set from the user State to the kernel state. This over

Vararr [{code ...} vararr2 [{code...}]; how to implement the transformation from arr to arr1, and how to implement a similar transformation of var arr = [if the code value is not only abc but also adsdsddsda223 [ {"Code": "a", "poll": 7 },{ "

I believe poll and epoll have been used to read this article. Let's look at the source code of the poll system call. asmlinkage long sys_poll(struct pollfd __user * ufds, unsigned int nfds, long timeout){struct poll_wqueues table;int fdcount, err;unsigned int i;struct poll_list *head;struct poll_list *walk;/* Do a sanity check on nfds ... */if (nfds > current->f

multiplexed I/O Model poll () Model Code implementationThe poll () mechanism is similar to the select () mechanism, and is a way to poll multiple descriptors.The difference is that poll () does not have a limit on the number of descriptors.is to

Preface This section describes how to use basic Linux/Unix functions and poll calls to compile a complete server and client example that can be run on Linux (UBUNTU) and Unix (FreeBSD, the functions of the client and server are as follows: The client reads a row from the standard input and sends it to the server. The server reads a row from the network and then outputs the row to the client. The client receives a response from the server and o

Poll for linux drivers and poll for linux driversPOLL operations 1. POLL execution process: Poll is a system call. Its kernel entry function is sys_poll. sys_poll calls do_sys_poll directly without any processing. The execution process of do_sys_poll can be divided into three parts: 1. Copy the input pollfd array to th

Linux Kernel 3.11 socket busy poll mechanism to avoid sleep switching, 3.11 pollThe network protocol stack of Linux is very independent. The upstream and downstream interfaces are connected to the user State and devices respectively. They can also be seen as North and South interfaces... the north direction uses the socket interface and the south direction uses the qdisc interface (you can think of it as the upper-layer netdev queue. For the receiving

Linux select and poll implementation mechanism and instance analysis, poll instance analysisWe can implement blocking operations until the upper layer combines select and poll for file operations. How exactly is this implemented?Select Interface:Int select (int nfds, fd_set * readset, fd_set * writeset,Fd_set * effectset, struct timeval * timeout );Where:NfdsNumb

With the full support of the 2.6 kernel to epoll, many articles and sample code on the network provide a message that using Epoll instead of the traditional poll can bring a performance boost to Web service applications. But most of the reasons for performance improvements are less explained here, I'll try to analyze how poll and epoll work in the kernel (2.6.21.

/* Echo server implemented by poll. author: thinkmay */# include

have just changed to ready state, it only says it once, if we do not take action, then it will not tell again, this method is called edge triggering. In theory, edge triggering has a higher performance, but the code implementation is quite complicated. 4. MMAP accelerates information transmission between the kernel and the user space. Epoll uses the same memory as the user space MMAP through the kernel to avoid unnecessary memory copies. 3.5 epoll mo

the 2.6.31 kernel for the Select function: They call the relationship: Select--> sys_select--> core_sys_select-- Gt Do_select int do_select (int n, fd_set_bits *fds, struct Timespec *end_time) {ktime_t expire, *to = NULL; struct Poll_wqueues table; Poll_table *wait; int retval, I, timed_out = 0; unsigned long slack = 0; This reduces the number of traversal loops in order to get the maximum descriptor in the collection. That is why the first parameter of select in Linux

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

functions include sys_open, sys_read, sys_write, and sys_poll. I. kernel framework: For the system to call poll or select, the corresponding kernel functions are sys_poll. Analyze sys_poll to understand the poll mechanism. 1. The sys_poll function is located in the fs/select. c file. The Code is as follows: asmlinkagelong sys_poll(struct pollfd __user *ufds, un

SelectThe essence is to use 32-bit 32-bit integer, that is, 32*32 = 1024, And the FD value is 1-1024. When the FD value exceeds the 1024 limit, you must modify the fd_setsize. In this case, you can identify the FD in the 32 * max value range. Select is not suitable for scenarios where a single process is multi-threaded and each thread processes multiple FD operations. 1. All threads scan from 1-32 * max, and each thread processes a FD value, which is a waste. 2.1024 upper limit. For a proc

All rights reserved. For more information, see all right reserved and copyright by Xu Xing. We have analyzed the kernel execution process caused by system calls in detail. This article will continue to analyze the poll function in the kernel source code of linux2.6.38 (similar to the select implementation, the two are essentially the same, because the implementation mechanism is the same, and the middle-lev

values:EBADF the file descriptor specified in one or more structs is invalid.The address that the Efaultfds pointer points to exceeds the address space of the process.Eintr the requested event before generating a signal that the call can be re-initiated.The Einvalnfds parameter exceeds the Plimit_nofile value.Enomem There is not enough memory available to complete the request. 3, enter data and echo through poll to stdin, timeout set to 5000ms

wake_up_locked_poll (ctx->wqh, Pollin); 5} At this point, the complete wake-up notification process is complete.The Select () implementation process is exactly the same as poll (), and the different FD and result events to be detected are returned in different ways. The poll () is internally recorded using a linked list, and select () is recorded using a bit sequence.For details, see the implementat

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 corresponding kernel functions are sys_poll. Analyze sys_poll to understand the poll mechanism. 1. The sys_poll function is located in the FS/select. c file. The Code is as follows: Asmlinkagelong sys_poll (struct p

{Code ...} the above is the php code, and then I strace it, the result is as follows {code ...} after sending the get command in line 3, poll is called. The timeout value is the value of line 0, 1572, and the value of timeout is 2000. Why do I need to call poll twice... $hos