redis-Network event Model (Scoket)

1. Related Macros and function prototypes
Fd_zero (int fd, fd_set* FDS)  fd_set (int fd, fd_set* FDS)  fd_isset (int fd, fd_set* FDS)  fd_clr (int fd, fd_set* FDS)  int Select (int Nfds, fd_set *readfds, Fd_set *writefds, fd_set *exceptfds,         struct timeval *timeout)
Here, the Fd_set type can be simply understood as a queue that marks a handle by bit, for example to mark a handle with a value of 16 in a fd_set, and the 16th bit bit of the fd_set is marked as 1. Specific placement, validation can be achieved using Fd_set, Fd_isset and other macros. In the Select () function, Readfds, Writefds, and Exceptfds are both input and output parameters. If the input Readfds is marked with a number 16th handle, select () detects whether the 16th handle is readable. After select () is returned, you can determine whether the "readable" event occurs by checking if the Readfds has a 16th-number handle. In addition, the user can set timeout time.
2. Server operation process

It should be noted here that a connect () operation on the client will fire a "readable event" on the server side, so select () can also detect the Connect () behavior from the client.

In the above model, the most critical place is how to dynamically maintain the three parameters of select () Readfds, Writefds, and Exceptfds. As an input parameter, Readfds should mark all the handles of the "readable event" that need to be probed, which will always include the "parent" handle that probes for connect (), and Writefds and Exceptfds should mark all "writable events" and "error events" that need to be probed. Handle (using the Fd_set () tag).

As an output parameter, the handle values of all events captured by select () are saved in Readfds, Writefds, and Exceptfds. The programmer needs to check all the token bits (using the Fd_isset () check) to determine exactly which handles have occurred.

The above model mainly simulates is "a ask a reply" service flow, so if select () found a handle caught "readable event", the server program should do recv () operation in time, and according to the received data ready to send data, and the corresponding handle value added to Writefds, Prepares the next "writable event" of the Select () probe. Similarly, if select () finds a handle that snaps to a writable event, the program should do a send () operation in time and prepare for the next "readable event" probe. Describes one of the execution cycles in the above model.

redis-Network event Model (Scoket)