poll code

Select, poll, epoll (2), pollepoll1. Select source code parsing is based on kernel code 2.6.28. select mainly contains four functions.Sys_select: process the time parameter, and then call core_sys_select.Core_sys_select: process three fd_set parameters (in, out, ex), and then call do_select.Do_select: traverses all fd and performs select/

Poll Mechanism analysisVedon 2009.12.10All 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 corres

Poll is a mechanism for monitoring whether a file is readable, as with select.The calling function for the application is as follows:int poll (struct POLLFD *fds,nfds_t nfds, int timeout);The poll mechanism will determine whether the file in the FDS is readable, if it is readable, it returns immediately, the value returned is the number of readable FD, if it is u

interrupts), which wakes up the dormant main process;5.sys_select's Poll_schedule_timeout function returns, no longer sleeps6. Once again, the poll function driven by the monitored device is called one at a time, which is availableDevice corresponding to the driver poll function will return non 0;7.if (ret | | time_out | | ...)//ret = 1, return immediately to user empty, the return value is RET valueSummar

= FDS-> ex; Rinp= FDS-> res_in; routp = FDS-> res_out; rexp = FDS-> res_ex; @-411,10 + 436,10 @ intDo_select (int n, fd_set_bits * FDS, S To= Expire; } -If(! Schedule_hrtimeout_range (to, slack, hrtimer_mode_abs )) + If(! Poll_schedule_timeout ( table, task_interruptible, + To, slack )) Timed_out= 1; } -_ Set_current_state (task_running ); Poll_freewait ( table ); We can see that in this sleep poll patch, we removed the statements deliberately added

(2) The other side of the socket communication closes the connection, at which time the read operation of the socket will return 0(3) A new connection request is on the monitor socket(4) There are unhandled errors on the socket(5) Socket core send buffer is greater than its low water level byte So_sndlowat(6) After the socket uses a non-blocking connect connection for success or failure(7) There are unhandled errors on the socketSpecific ExamplesRefer to the pseudo-

of this descriptor will be ignored, that is, the member variable events will not be detected, events registered on events are also ignored. When the poll () function returns, the member variable revents is set to 0, indicating that no event has occurred; In addition, the poll () function will not be affected and restricted by the o_ndelay mark and o_nonblock mark on the socket descriptor, that is, whether

lists the file descriptor ready for I/O, but does not wait for other events. In this case, poll (), like its name, returns as soon as it is elected.On success, poll () returns the number of file descriptors that are not 0 in the Revents field in the struct, and if no events occur before the timeout, poll () returns 0; when failed,

The first thing we need to know about select,poll,epoll is The mechanism of 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 be responsib

equivalent of a combination of the settings in the Select array to hold the file descriptor and add the settings of the two steps, each time the poll will occur when the event is ready to the corresponding revents set, when the processing is completed by the system automatically attributed to 0, Manual initialization is not required to clear 0; Before a struct array is used, the struct member FD, events, and revents are random values, just like t

Select, poll, epoll (2)1. Select source code parsing is based on kernel code 2.6.28. select mainly contains four functions.Sys_select: process the time parameter, and then call core_sys_select.Core_sys_select: process three fd_set parameters (in, out, ex), and then call do_select.Do_select: traverses all fd and performs select/