#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <assert.h>

#define BLOCK_SIZE 8192
#define INIT_SEED 1999
#define MAX_THREADS 8

size_t file_size;
char* file_name;
size_t n_prefetchers = 1;
int  use_fadvise;
int n_iterations = 10*1024*1024;

static off_t random_offset(uint64_t* seed)
{
	off_t rnd =  (3141592621u * *seed + 2718281829u) % 1000000007u;
	*seed = rnd;
	return rnd % file_size * BLOCK_SIZE;
}

void reader(void)
{
	uint64_t seed = INIT_SEED;
	char page[BLOCK_SIZE];
	time_t start = time(NULL);
	int i;
	int fd = open(file_name, O_RDONLY);
	assert(fd >= 0);

	for (i = 0; i < n_iterations; i++) {
		off_t offs = random_offset(&seed);
		ssize_t rc = pread(fd, page, sizeof page, offs);
		time_t now;
		assert(rc == BLOCK_SIZE);
		now = time(NULL);
		if (i % 1024 == 0 && now != start) {
			printf("%d: %.2f Mb/sec   \r", i/1024, (double)(i+1)*BLOCK_SIZE/1024/1024/(now - start));
			fflush(stdout);
		}
	}
}

void* prefetcher(void* arg)
{
	size_t id = (size_t)arg;
	uint64_t seed = INIT_SEED;
	char page[BLOCK_SIZE];
	int fd = open(file_name, O_RDONLY);
	int i;
	assert(fd >= 0);

	for (i = 0;;i++) {
		off_t offs = random_offset(&seed);
		if (i % n_prefetchers == id) { 
			if (use_fadvise) {
				int rc = posix_fadvise(fd, offs, BLOCK_SIZE, POSIX_FADV_WILLNEED);
				assert(rc == 0);
			} else { 
				ssize_t rc = pread(fd, page, sizeof page, offs);
				assert(rc == BLOCK_SIZE);
			}
		}
	}
	return 0;
}

int main(int argc, char* argv[])
{
	pthread_t prefetchers[MAX_THREADS];
	int i;
	int fd;

	for (i = 1; i < argc; i++) {
		if (argv[i][0] == '-') {
			switch (argv[i][1]) {
			  case 'f':
				use_fadvise = 1;
				continue;
			  case 'n':
				n_prefetchers = atoi(argv[++i]);
				continue;
			  case 'i':
				n_iterations = atoi(argv[++i]);
				continue;
			  default:
			  help:
				fprintf(stderr, "prefetch [-f] [-n THREADS] [-i ITERATIONS] file\n");
				return 1;
			}
		} else {
			file_name = argv[i];
		}
	}
	if (file_name == NULL) {
		goto help;
	}
  	fd = open(file_name, O_RDONLY);
	assert(fd >= 0);
	file_size = lseek(fd, 0, SEEK_END)/BLOCK_SIZE;
	assert(file_size != 0);

	for (i = 0; i < n_prefetchers; i++) {
		pthread_create(&prefetchers[i], NULL, prefetcher, (void*)(size_t)i);
	}

	reader();
	puts("\nDone");
	return 0;
}