Linux EVENTFD ()

Reference: http://www.man7.org/linux/man-pages/man2/eventfd.2.html

First, Introduction

Simply put, the function is to create a file descriptor for the event notification. It is similar to a pipe, but does not require two descriptors like a pipe, it requires only a description to enable interprocess communication.

For a detailed introduction, see Resources.

Second, use

Example:

#include <sys/eventfd.h>#include<unistd.h>#include<stdlib.h>#include<stdio.h>#include<stdint.h>/*Definition of uint64_t*/#defineHandle_error (msg) Do{perror (msg); exit (exit_failure);} while(0)intMainintargcChar**argv) {    intEFD, J;    uint64_t u;    ssize_t s; if(ARGC <2) {fprintf (stderr,"Usage:%s <num>...\n", argv[0]);    Exit (Exit_failure); } EFD= EVENTFD (0,0); if(EFD = =-1) {Handle_error ("EVENTFD"); }    Switch(fork ()) { Case 0:             for(j =1; J < argc; J + +) {printf ("Child writing%s to efd\n", Argv[j]); U= Strtoull (Argv[j], NULL,0); S= Write (EFD, &u,sizeof(uint64_t)); if(s! =sizeof(uint64_t)) {Handle_error ("Write"); }} printf ("Child completed write loop\n");        Exit (exit_success);  Case-1: Handle_error ("Fork"); default: Sleep (2); printf ("Parent About to read\n"); S= Read (EFD, &u,sizeof(uint64_t)); if(s! =sizeof(uint64_t)) {Handle_error ("Read"); } printf ("Parent Read%llu (0X%LLX) from efd\n", (unsignedLong Long) u, (unsignedLong Long) u);    Exit (exit_success); }}

Execution Result:

Third, the question

Why write the number of this file descriptor, read to incredibly is their and?

See, take a closer look at the read, write operation on the file descriptor, read reads an integer of type uini64_t from the file descriptor, and write adds the number to be written to an existing integer.

Linux EVENTFD ()