/*
 * gcc -Wall -o reader reader.c -lpthread
 */
#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/sendfile.h>
#include <unistd.h>
#include <errno.h>
#include <err.h>
#include <pthread.h>

struct thread_data {
	int fd;
	int read_size;
	size_t size;
};

static void *drop_pages(void *arg)
{
	struct thread_data *td = arg;
	int ret;

	while (1) {
		ret = posix_fadvise(td->fd,  0, td->size, POSIX_FADV_DONTNEED);
		if (ret < 0)
			err(1, "fadvise dontneed");
	}
	return NULL;
}

#define READ_BUF (2 * 1024 * 1024)
static void *read_pages(void *arg)
{
	struct thread_data *td = arg;
	char buf[READ_BUF];
	ssize_t ret;
	loff_t offset = 8192;

	while (1) {
		ret = pread(td->fd, buf, td->read_size, offset);
		if (ret < 0)
			err(1, "read");
		if (ret == 0)
			break;
	}
	return NULL;
}

int main(int ac, char **av)
{
	int fd;
	int ret;
	struct stat st;
	int sizes[9] = { 0, 0, 8192, 16834, 32768, 65536, 128 * 1024, 256 * 1024, 1024 * 1024 };
	int nr_tids = 9;
	struct thread_data tds[9];
	int i;
	int sleeps = 0;
	pthread_t tids[nr_tids];

	if (ac != 2)
		err(1, "usage: reader filename\n");

	fd = open(av[1], O_RDONLY, 0600);
	if (fd < 0)
		err(1, "unable to open %s", av[1]);

	ret = fstat(fd, &st);
	if (ret < 0)
		err(1, "stat");


	for (i = 0; i < nr_tids; i++) {
		struct thread_data *td = tds + i;

		td->fd = fd;
		td->size = st.st_size;
		td->read_size = sizes[i];

		if (i < 2)
			ret = pthread_create(tids + i, NULL, drop_pages, td);
		else
			ret = pthread_create(tids + i, NULL, read_pages, td);
		if (ret)
			err(1, "pthread_create");
	}
	for (i = 0; i < nr_tids; i++) {
		pthread_detach(tids[i]);
	}
	while(1) {
		sleep(122);
		sleeps++;
		fprintf(stderr, ":%d:", sleeps * 122);

	}
}