path: root/playlist.c

#include <asm-generic/errno-base.h>
#include <errno.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "playlist.h"

#define PLAYLIST_INIT_SIZE 2 // TODO: Bump to 32

struct Playlist {
	struct Entry *entries;
	int front, rear, next_id, len, size;
	pthread_mutex_t mutex;
	pthread_cond_t  ready;
};

static int  playlist_grow           (Playlist *pl);
static int  playlist_is_full        (Playlist *pl);
static int  playlist_is_empty       (Playlist *pl);
static int  playlist_get_index      (Playlist *pl, unsigned int id);
static void playlist_unsafe_dequeue (Playlist *pl, struct Entry *entry);

Playlist *playlist_init(void)
{
	Playlist *pl;

	if ((pl = malloc(sizeof(*pl))) == NULL)
		return NULL;

	pl->entries = calloc(PLAYLIST_INIT_SIZE, sizeof(*pl->entries));
	if (pl->entries == NULL) {
		free(pl);
		return NULL;
	}

	pl->next_id = 0;
	pl->front  = 0;
	pl->rear   = 0;
	pl->len    = 0;
	pl->size   = PLAYLIST_INIT_SIZE;
	pl->mutex  = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
	pl->ready  = (pthread_cond_t) PTHREAD_COND_INITIALIZER;
	return pl;
}

void playlist_free (Playlist *pl)
{
	int i;

	if (pl == NULL)
		return;

	for (i = 0; i < pl->size; i ++)
		free(pl->entries[0].file);

	free(pl->entries);
	free(pl);
}

int playlist_enqueue (Playlist *pl, const char *entry)
{
	int id;
	char *copy;

	if ((copy = strdup(entry)) == NULL)
		return -1;

	pthread_mutex_lock(&pl->mutex);
	if (playlist_is_full(pl) && playlist_grow(pl)) {
		pthread_mutex_unlock(&pl->mutex);
		free(copy);
		return -1;
	}

	pl->entries[pl->rear].file = copy;
	id = pl->entries[pl->rear].id = pl->next_id ++;
	pl->rear = (pl->rear + 1) % pl->size;
	pl->len ++;

	pthread_cond_signal(&pl->ready);
	pthread_mutex_unlock(&pl->mutex);
	return id;
}

int playlist_dequeue (Playlist *pl, struct Entry *entry)
{
	/* playlist_dequeue take hold of the playlist's mutex, relinquishing it
	 * either after a song has been dequeued, or, in the scenario where the
	 * playlist is currently empty, atomically while waiting for the pl->ready
	 * condition to signal true, indicating that a song has been queued.
	 *
	 * However, it is documented that POSIX condition waiters may be subjects to
	 * "spurious wakeup", spontaneously unlocking themself for no appearent
	 * reasons.
	 *
	 * To prevent undefined behaviours, the lock condition checker and the
	 * waiter are placed in a loop to ensure that any return-to-context occured
	 * legitimately, and to keep waiting othwerwise.
	 */

	pthread_mutex_lock(&pl->mutex);
	errno = 0;
	while (playlist_is_empty(pl)) {
		pthread_cond_wait(&pl->ready, &pl->mutex);
		if (errno) {
			pthread_mutex_unlock(&pl->mutex);
			return -1;
		}
	}

	playlist_unsafe_dequeue(pl, entry);
	pthread_mutex_unlock(&pl->mutex);
	return 0;
}

int playlist_try_dequeue(Playlist *pl, struct Entry *entry)
{
	pthread_mutex_lock(&pl->mutex);
	if (playlist_is_empty(pl)) {
		pthread_mutex_unlock(&pl->mutex);
		return -1;
	}

	playlist_unsafe_dequeue(pl, entry);
	pthread_mutex_unlock(&pl->mutex);
	return 0;
}

int playlist_remove(Playlist *pl, unsigned int id, struct Entry *entry)
{
	int index;

	pthread_mutex_lock(&pl->mutex);
	if ((index = playlist_get_index(pl, id)) == -1) {
		pthread_mutex_unlock(&pl->mutex);
		return -1;
	}

	*entry = pl->entries[index];
	while (index != pl->rear) {
		pl->entries[index] = pl->entries[index + 1];
		index = (index + 1) % pl->len;
	}

	if (pl->rear -- < 0)
		pl->rear = pl->len - 1;
	pl->len --;

	pthread_mutex_unlock(&pl->mutex);
	return 0;
}

int playlist_insert(Playlist *pl, unsigned int id, const char *value)
{
	char *copy;
	int index, new_id;
	struct Entry a, b;

	pthread_mutex_lock(&pl->mutex);
	if ((index = playlist_get_index(pl, id)) == -1) {
		pthread_mutex_unlock(&pl->mutex);
		return -1;
	}

	if ((copy = strdup(value)) == NULL)
		goto enomem;

	if (playlist_is_full(pl) && playlist_grow(pl))
		goto enomem;

	pl->rear = (pl->rear + 1) % pl->len;

	a = (struct Entry){ new_id = pl->next_id ++, copy };
	while (index != pl->rear) {
		b = pl->entries[index];
		pl->entries[index] = a;
		a = b;
		index = (index + 1) % pl->len;
	}

	pl->len ++;

	pthread_mutex_unlock(&pl->mutex);
	return new_id;

enomem:
	pthread_mutex_unlock(&pl->mutex);
	free(copy);
	return -2;
}

int playlist_list(Playlist *pl, struct StateInfo *list)
{
	int i, j;

	pthread_mutex_lock(&pl->mutex);
	list->song_count = pl->len;
	if ((list->next_songs = malloc(sizeof(list[0]) * pl->len)) == NULL)
		return -1;

	for (i = 0, j = pl->front; i < pl->len; i ++, j ++) {
		j %= pl->len;
		list->next_songs[i].id = pl->entries[j].id;
		list->next_songs[i].file = strdup(pl->entries[j].file);
	}
	pthread_mutex_unlock(&pl->mutex);

	return 0;
}

int playlist_get_index(Playlist *pl, unsigned int id)
{
	int index;

	index = pl->front;

	// Break on a null entry
	while (pl->entries[index].file) {
		// Bingo
		if (pl->entries[index].id == id)
			return index;

		// Advance the index, and break if we're back at the front
		index = (index + 1) % pl->len;
		if (index == pl->front)
			break;
	}

	return -1;
}

static int playlist_is_full (Playlist *pl)
{
	return pl->len == pl->size;
}

static int playlist_is_empty (Playlist *pl)
{
	return pl->entries[pl->front].file == NULL;
}

static int playlist_grow(Playlist *pl)
{
	int split;
	struct Entry *new_buff;

	new_buff = calloc(pl->size * 2, sizeof(*new_buff));
	if (new_buff == NULL) return -1;

	split = pl->len - pl->front;
	memcpy(&new_buff[0], &pl->entries[pl->front], split);
	memcpy(&new_buff[split], &pl->entries[0], pl->len - split);

	free(pl->entries);
	pl->front = 0;
	pl->rear = pl->len;
	pl->entries = new_buff;
	pl->size *= 2;
	return 0;
}

static void playlist_unsafe_dequeue(Playlist *pl, struct Entry *entry)
{
	*entry = pl->entries[pl->front];
	pl->entries[pl->front].file = NULL;
	pl->front = (pl->front + 1) % pl->size;
	pl->len --;
}