#define _GNU_SOURCE

#include<stdio.h>

#include<stdlib.h>

#include<unistd.h>

#include<fcntl.h>

#include<sys/types.h>

#include<sys/stat.h>

#include<libaio.h>

#include<pthread.h>

#include<errno.h>

#define MAXEVENTS 100

#define PATH "Testfilenew.txt"

#define BUFFERSIZE 4096

/*

* Demonstrate asynchronous readss from a File using libaio

* Separate Threads are maintained for submitting and reaping IO requests

* Files should be opened using the O_DIRECT flag compulsorily

* For GNU compliant systems only

* @Author : Akhil Rao

*/

io_context_t context; /* Context of the application */

int filedes; /* file descriptor */

char* buffer; /* buffer for data excahnge */

void SubmitRead(int offset);

void *Reap(void *p);

int main(){

int i;

pthread_t reaperThread;

/* memory alignment is very essential for memory writes*/

posix_memalign((void**)&buffer,BUFFERSIZE,BUFFERSIZE);

filedes=open(PATH,O_RDONLY|O_DIRECT,0644); /* Open the file for reading */

if(filedes<0){

printf("Error Opening File\n");

return 0;

}

io_setup(MAXEVENTS,&context); /* Initialize context */

/* Create a separate thread to process results */

pthread_create(&reaperThread,NULL,Reap,(void *)&i);

for(i=0;i<100;i++){

SubmitRead(i); /* Submit Requests for Reading */

}

pthread_join(reaperThread,NULL); /* Wait till reaperThread Exits */

/* Deallocate file descriptor and the context */

close(filedes);

io_destroy(context);

return 0;

}

/* Submits the read IO request */

void SubmitRead(int offset){

int x;

struct iocb iocbr;

struct iocb *iocbrp=&iocbr;

/* Init iocb structure */

io_prep_pread(&iocbr,filedes,buffer,BUFFERSIZE,BUFFERSIZE*offset);

iocbr.data=(void*)buffer;

x=io_submit(context,1,&iocbrp); /* Submit the request */

if(x<0)

printf("Error while submitting read request\n %d",x);

}

/* Reaps the outcome of IO requests submitted till now */

void *Reap(void *dummy){

struct io_event list[MAXEVENTS];

int events_completed=0,k=0,j,i; /*

char str[4097]={0},*data;

struct timespec timeout; /* timeout of 1 second */

timeout.tv_sec=1;

timeout.tv_nsec=0;

printf("Starting Reaping Events");

while(k<100){

/* obtain the list of requests completed */

events_completed=io_getevents(context,1,5,list,&timeout);

k+=events_completed;

for(i=0;i<events_completed;i++){

data=(char *)list[i].data;

for(j=0;j<list[i].res;j++){

str[j]=data[j];

}

printf("%ld %s\n\n",list[i].res,str); /* Print the data read */

}

}

}