X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=mood.c;h=1e15ef0e081480381fcbc4fdad2179848f429c1f;hp=5268e77fe03c7e56d1b146935f683e30dea9a2f6;hb=HEAD;hpb=19c6002ccd47b720b53410d0cbbecdae6ba80223

diff --git a/mood.c b/mood.c
index 5268e77f..1e15ef0e 100644
--- a/mood.c
+++ b/mood.c
@@ -12,8 +12,6 @@
 #include "afh.h"
 #include "afs.h"
 #include "list.h"
-#include "mm.h"
-#include "mood.h"
 
 /*
  * Mood parser API. It's overkill to have an own header file for
@@ -39,55 +37,40 @@ struct afs_statistics {
 	int64_t num_played_qd;
 	/** Quadratic deviation of last played time. */
 	int64_t last_played_qd;
+	/** Correction factor for the num played score. */
+	int64_t num_played_correction;
+	/** Correction factor for the last played score. */
+	int64_t last_played_correction;
+	/** Common divisor of the correction factors. */
+	int64_t normalization_divisor;
 	/** Number of admissible files */
 	unsigned num;
 };
-static struct afs_statistics statistics;
 
 /**
- * Each line of the current mood corresponds to a mood_item.
- */
-struct mood_item {
-	/** The method this line is referring to. */
-	const struct mood_method *method;
-	/** The data structure computed by the mood parser. */
-	void *parser_data;
-	/** The given score value, or zero if none was given. */
-	int32_t score_arg;
-	/** Non-zero if random scoring was requested. */
-	int random_score;
-	/** Whether the "not" keyword was given in the mood line. */
-	int logical_not;
-	/** The position in the list of items. */
-	struct list_head mood_item_node;
-};
-
-/*
- * Created from the mood definition by \ref change_current_mood().
+ * Stores an instance of a loaded mood (parser and statistics).
  *
- * When a mood is opened, each line of its definition is investigated, and a
- * corresponding mood item is produced. Each mood line starts with accept,
- * deny, or score which determines the type of the mood line. For each such
- * type a linked list is maintained whose entries are the mood items.
+ * A structure of this type is allocated and initialized when a mood is loaded.
  */
-struct mood {
-	/** The name of this mood. */
+struct mood_instance {
+	/** NULL means that this is the "dummy" mood. */
 	char *name;
-	/** The list of mood items of type \p accept. */
-	struct list_head accept_list;
-	/** The list of mood items of type \p deny. */
-	struct list_head deny_list;
-	/** The list of mood items of type \p score. */
-	struct list_head score_list;
-	/* Only used for version 2 moods. */
+	/** Bison's abstract syntax tree, used to determine admissibility. */
 	struct mp_context *parser_context;
+	/** To compute the score. */
+	struct afs_statistics stats;
+	/** NULL means to operate on the global score table. */
+	struct osl_table *score_table;
 };
 
 /*
- * If current_mood is NULL then no mood is currently open. If
- * current_mood->name is NULL, the dummy mood is currently open.
+ * If current_mood is NULL then no mood is currently loaded. If
+ * current_mood->name is NULL, the current mood is the dummy mood.
+ *
+ * The statistics are adjusted dynamically through this pointer as files are
+ * added, removed or played.
  */
-static struct mood *current_mood;
+static struct mood_instance *current_mood;
 
 /*
  * Find the position of the most-significant set bit.
@@ -146,338 +129,76 @@ __a_const static uint64_t int_sqrt(uint64_t x)
 	return res;
 }
 
-/*
- * Returns true if row matches, false if it does not match. In any case score
- * and score_arg_sum are set/increased accordingly.
- */
-static bool get_item_score(struct mood_item *item, const struct afs_info *afsi,
-		const struct afh_info *afhi, const char *path, long *score,
-		long *score_arg_sum)
-{
-	int ret;
-	bool match = true;
-
-	*score_arg_sum += item->random_score? 100 : PARA_ABS(item->score_arg);
-	ret = 100;
-	if (item->method) {
-		ret = item->method->score_function(path, afsi, afhi,
-			item->parser_data);
-		if ((ret < 0 && !item->logical_not) || (ret >= 0 && item->logical_not))
-			match = false;
-	}
-	if (item->random_score)
-		*score = PARA_ABS(ret) * para_random(100);
-	else
-		*score = PARA_ABS(ret) * item->score_arg;
-	return match;
-}
-
-/* returns 1 if row admissible, 0 if not, negative on errors */
-static int row_is_admissible(const struct osl_row *aft_row, struct mood *m,
-		long *scorep)
+static void destroy_mood(struct mood_instance *m)
 {
-	struct mood_item *item;
-	int ret;
-	bool match;
-	long score_arg_sum = 0, score = 0, item_score;
-	struct afs_info afsi;
-	struct afh_info afhi;
-	char *path;
-
-	if (!m)
-		return -E_NO_MOOD;
-	if (m->parser_context) {
-		*scorep = 0;
-		return mp_eval_row(aft_row, m->parser_context);
-	}
-	ret = get_afsi_of_row(aft_row, &afsi);
-	if (ret < 0)
-		return ret;
-	ret = get_afhi_of_row(aft_row, &afhi);
-	if (ret < 0)
-		return ret;
-	ret = get_audio_file_path_of_row(aft_row, &path);
-	if (ret < 0)
-		return ret;
-	/* reject audio file if it matches any entry in the deny list */
-	list_for_each_entry(item, &m->deny_list, mood_item_node) {
-		match = get_item_score(item, &afsi, &afhi, path, &item_score,
-			&score_arg_sum);
-		if (match) /* not admissible */
-			return 0;
-		score += item_score;
-	}
-	match = false;
-	list_for_each_entry(item, &m->accept_list, mood_item_node) {
-		ret = get_item_score(item, &afsi, &afhi, path, &item_score,
-			&score_arg_sum);
-		if (ret == 0)
-			continue;
-		match = true;
-		score += item_score;
-	}
-	/* reject if there is no matching entry in the accept list */
-	if (!match && !list_empty(&m->accept_list))
-		return 0;
-	list_for_each_entry(item, &m->score_list, mood_item_node) {
-		match = get_item_score(item, &afsi, &afhi, path, &item_score,
-			&score_arg_sum);
-		if (match)
-			score += item_score;
-	}
-	if (score_arg_sum)
-		score /= score_arg_sum;
-	*scorep = score;
-	return 1;
-}
-
-static void cleanup_list_entry(struct mood_item *item)
-{
-	if (item->method && item->method->cleanup)
-		item->method->cleanup(item->parser_data);
-	else
-		free(item->parser_data);
-	list_del(&item->mood_item_node);
-	free(item);
-}
-
-static void destroy_mood(struct mood *m)
-{
-	struct mood_item *tmp, *item;
-
 	if (!m)
 		return;
-	list_for_each_entry_safe(item, tmp, &m->accept_list, mood_item_node)
-		cleanup_list_entry(item);
-	list_for_each_entry_safe(item, tmp, &m->deny_list, mood_item_node)
-		cleanup_list_entry(item);
-	list_for_each_entry_safe(item, tmp, &m->score_list, mood_item_node)
-		cleanup_list_entry(item);
-	free(m->name);
 	mp_shutdown(m->parser_context);
+	if (m->score_table)
+		score_close(m->score_table);
+	free(m->name);
 	free(m);
 }
 
-static struct mood *alloc_new_mood(const char *name)
+static struct mood_instance *alloc_new_mood(const char *name)
 {
-	struct mood *m = para_calloc(sizeof(struct mood));
+	struct mood_instance *m = zalloc(sizeof(*m));
+
 	if (name)
 		m->name = para_strdup(name);
-	INIT_LIST_HEAD(&m->accept_list);
-	INIT_LIST_HEAD(&m->deny_list);
-	INIT_LIST_HEAD(&m->score_list);
+	m->stats.normalization_divisor = 1;
 	return m;
 }
 
-/** The different types of a mood line. */
-enum mood_line_type {
-	/** Invalid. */
-	ML_INVALID,
-	/** Accept line. */
-	ML_ACCEPT,
-	/** Deny line. */
-	ML_DENY,
-	/** Score line. */
-	ML_SCORE
-};
-
-/** Data passed to the parser of a mood line. */
-struct mood_line_parser_data {
-	/** The mood this mood line belongs to. */
-	struct mood *m;
-	/** The line number in the mood definition. */
-	unsigned line_num;
-};
-
-/*
- * <accept [with score <score>] | deny [with score <score>]  | score <score>>
- * 	[if] [not] <mood_method> [options]
- * <score> is either an integer or "random" which assigns a random score to
- * all matching files
- */
-static int parse_mood_line(char *mood_line, void *data)
-{
-	struct mood_line_parser_data *mlpd = data;
-	char **argv;
-	unsigned num_words;
-	char **w;
-	int i, ret;
-	enum mood_line_type mlt = ML_INVALID;
-	struct mood_item *mi = NULL;
-
-	mlpd->line_num++;
-	ret = create_argv(mood_line, " \t", &argv);
-	if (ret < 0)
-		return ret;
-	num_words = ret;
-	if (!num_words) /* empty line */
-		goto out;
-	w = argv;
-	if (**w == '#') /* comment */
-		goto out;
-	if (!strcmp(*w, "accept"))
-		mlt = ML_ACCEPT;
-	else if (!strcmp(*w, "deny"))
-		mlt = ML_DENY;
-	else if (!strcmp(*w, "score"))
-		mlt = ML_SCORE;
-	ret = -E_MOOD_SYNTAX;
-	if (mlt == ML_INVALID)
-		goto out;
-	mi = para_calloc(sizeof(struct mood_item));
-	if (mlt != ML_SCORE) {
-		ret = -E_MOOD_SYNTAX;
-		w++;
-		if (!*w)
-			goto out;
-		if (strcmp(*w, "with"))
-			goto check_for_if;
-		w++;
-		if (!*w)
-			goto out;
-		if (strcmp(*w, "score"))
-			goto out;
-	}
-	if (mlt == ML_SCORE || !strcmp(*w, "score")) {
-		ret = -E_MOOD_SYNTAX;
-		w++;
-		if (!*w)
-			goto out;
-		if (strcmp(*w, "random")) {
-			mi->random_score = 0;
-			ret = para_atoi32(*w, &mi->score_arg);
-			if (ret < 0)
-				goto out;
-		} else {
-			mi->random_score = 1;
-			if (!*(w + 1))
-			goto success; /* the line "score random" is valid */
-		}
-	} else
-		mi->score_arg = 0;
-	ret = -E_MOOD_SYNTAX;
-	w++;
-	if (!*w)
-		goto out;
-check_for_if:
-	if (!strcmp(*w, "if")) {
-		ret = -E_MOOD_SYNTAX;
-		w++;
-		if (!*w)
-			goto out;
-	}
-	if (!strcmp(*w, "not")) {
-		ret = -E_MOOD_SYNTAX;
-		w++;
-		if (!*w)
-			goto out;
-		mi->logical_not = 1;
-	} else
-		mi->logical_not = 0;
-	for (i = 0; mood_methods[i].parser; i++) {
-		if (strcmp(*w, mood_methods[i].name))
-			continue;
-		break;
-	}
-	ret = -E_MOOD_SYNTAX;
-	if (!mood_methods[i].parser)
-		goto out;
-	ret = mood_methods[i].parser(num_words - 1 - (w - argv), w,
-		&mi->parser_data);
-	if (ret < 0)
-		goto out;
-	mi->method = &mood_methods[i];
-success:
-	if (mlpd->m) {
-		if (mlt == ML_ACCEPT)
-			para_list_add(&mi->mood_item_node, &mlpd->m->accept_list);
-		else if (mlt == ML_DENY)
-			para_list_add(&mi->mood_item_node, &mlpd->m->deny_list);
-		else
-			para_list_add(&mi->mood_item_node, &mlpd->m->score_list);
-	}
-	PARA_DEBUG_LOG("%s entry added, method: %p\n", mlt == ML_ACCEPT? "accept" :
-		(mlt == ML_DENY? "deny" : "score"), mi->method);
-	ret = 1;
-out:
-	free_argv(argv);
-	if (mi && (ret < 0 || !mlpd->m)) { /* mi was not added to any list */
-		free(mi->parser_data);
-		free(mi);
-	}
-	return ret;
-}
-
-static int load_mood(const struct osl_row *mood_row, struct mood **m,
-		char **errmsg)
+static int init_mood_parser(const char *mood_name, struct mood_instance **m,
+		char **err)
 {
-	char *mood_name;
 	struct osl_object mood_def;
-	struct mood_line_parser_data mlpd = {.line_num = 0};
 	int ret;
 
-	*m = NULL;
-	ret = mood_get_name_and_def_by_row(mood_row, &mood_name, &mood_def);
-	if (ret < 0) {
-		if (errmsg)
-			*errmsg = make_message(
-				"could not read mood definition");
-		return ret;
+	if (!*mood_name) {
+		if (err)
+			*err = make_message("empty mood name\n");
+		return -ERRNO_TO_PARA_ERROR(EINVAL);
 	}
-	assert(*mood_name);
-	mlpd.m = alloc_new_mood(mood_name);
-	ret = for_each_line(FELF_READ_ONLY, mood_def.data, mood_def.size,
-		parse_mood_line, &mlpd);
+	ret = mood_get_def_by_name(mood_name, &mood_def);
 	if (ret < 0) {
-		PARA_INFO_LOG("opening version 2 mood %s\n", mlpd.m->name);
-		ret = mp_init(mood_def.data, mood_def.size, &mlpd.m->parser_context,
-			errmsg);
-		if (ret < 0)
-			destroy_mood(mlpd.m);
-	} else {
-		PARA_WARNING_LOG("loaded version 1 mood %s\n", mlpd.m->name);
-		PARA_WARNING_LOG("please convert to version 2\n");
-		ret = 1;
+		if (err)
+			*err = make_message("could not read mood definition\n");
+		return ret;
 	}
+	*m = alloc_new_mood(mood_name);
+	PARA_INFO_LOG("loading mood %s\n", mood_name);
+	ret = mp_init(mood_def.data, mood_def.size, &(*m)->parser_context, err);
 	osl_close_disk_object(&mood_def);
-	if (ret >= 0)
-		*m = mlpd.m;
+	if (ret < 0)
+		destroy_mood(*m);
 	return ret;
 }
 
 static int check_mood(struct osl_row *mood_row, void *data)
 {
-	struct para_buffer *pb = data;
-	char *mood_name;
+	struct afs_callback_arg *aca = data;
+	char *mood_name, *errmsg;
 	struct osl_object mood_def;
-	struct mood_line_parser_data mlpd = {.line_num = 0};
-
+	struct mood_instance *m;
 	int ret = mood_get_name_and_def_by_row(mood_row, &mood_name, &mood_def);
 
 	if (ret < 0) {
-		para_printf(pb, "cannot read mood\n");
+		afs_error(aca, "cannot read mood\n");
 		return ret;
 	}
 	if (!*mood_name) /* ignore dummy row */
 		goto out;
-	ret = for_each_line(FELF_READ_ONLY, mood_def.data, mood_def.size,
-		parse_mood_line, &mlpd);
+	m = alloc_new_mood("check");
+	ret = mp_init(mood_def.data, mood_def.size, &m->parser_context,
+		&errmsg);
 	if (ret < 0) {
-		char *errmsg;
-		struct mood *m = alloc_new_mood("check");
-		ret = mp_init(mood_def.data, mood_def.size, &m->parser_context,
-			&errmsg);
-		if (ret < 0) {
-			para_printf(pb, "%s: %s\n", mood_name, errmsg);
-			free(errmsg);
-			para_printf(pb, "%s\n", para_strerror(-ret));
-		} else
-			destroy_mood(m);
-	} else {
-		para_printf(pb, "%s: v1 mood, please convert to v2\n",
-			mood_name);
-
-	}
+		afs_error(aca, "%s: %s\n%s\n", mood_name, errmsg,
+			para_strerror(-ret));
+		free(errmsg);
+	} else
+		destroy_mood(m);
 	ret = 1; /* don't fail the loop on invalid mood definitions */
 out:
 	osl_close_disk_object(&mood_def);
@@ -487,7 +208,7 @@ out:
 /**
  * Check all moods for syntax errors.
  *
- * \param aca Only ->pbout is used for diagnostics.
+ * \param aca Output goes to ->pbout, errors to ->fd on the error band.
  *
  * \return Negative on fatal errors. Inconsistent mood definitions are not
  * considered an error.
@@ -495,27 +216,67 @@ out:
 int mood_check_callback(struct afs_callback_arg *aca)
 {
 	para_printf(&aca->pbout, "checking moods...\n");
-	return osl(osl_rbtree_loop(moods_table, BLOBCOL_ID, &aca->pbout,
-		check_mood));
+	return osl(osl_rbtree_loop(moods_table, BLOBCOL_ID, aca, check_mood));
 }
 
-static int64_t normalized_value(int64_t x, int64_t n, int64_t sum, int64_t qd)
-{
-	if (!n || !qd)
-		return 0;
-	return 100 * (n * x - sum) / (int64_t)int_sqrt(n) / (int64_t)int_sqrt(qd);
-}
-
-static long compute_score(struct afs_info *afsi, long mood_score)
+/*
+ * The normalized num_played and last_played values are defined as
+ *
+ *	nn := -(np - mean_n) / sigma_n and nl := -(lp - mean_l) / sigma_l
+ *
+ *  For a (hypothetical) file with np = 0 and lp = now we thus have
+ *
+ *	nn =  mean_n / sigma_n =: hn > 0
+ *	nl = -(now - mean_l) / sigma_l =: hl < 0
+ *
+ * We design the score function so that both contributions get the same
+ * weight. Define the np and lp score of an arbitrary file as
+ *
+ *	sn := nn * -hl and sl := nl * hn
+ *
+ * Example:
+ *	num_played mean/sigma: 87/14
+ *	last_played mean/sigma: 45/32 days
+ *
+ *	We have hn = 87 / 14 = 6.21 and hl = -45 / 32 = -1.41. Multiplying
+ *	nn of every file with the correction factor 1.41 and nl with
+ *	6.21 makes the weight of the two contributions equal.
+ *
+ * The total score s := sn + sl has the representation
+ *
+ *	s = -cn * (np - mean_n) - cl * (lp - mean_l)
+ *
+ * with positive correction factors
+ *
+ *	cn = (now - mean_l) / (sqrt(ql) * sqrt(qn) / n)
+ *	cl = mean_n / (sqrt(ql) * sqrt(qn) / n)
+ *
+ * where ql and qn are the quadratic deviations stored in the statistics
+ * structure and n is the number of admissible files. To avoid integer
+ * overflows and rounding errors we store the common divisor of the
+ * correction factors separately.
+ */
+static long compute_score(struct afs_info *afsi,
+		const struct afs_statistics *stats)
 {
-	mood_score -= normalized_value(afsi->num_played, statistics.num,
-		statistics.num_played_sum, statistics.num_played_qd);
-	mood_score -= normalized_value(afsi->last_played, statistics.num,
-		statistics.last_played_sum, statistics.last_played_qd);
-	return mood_score / 3;
+	int64_t mean_n, mean_l,score_n, score_l;
+
+	assert(stats->normalization_divisor > 0);
+	assert(stats->num > 0);
+	mean_n = stats->num_played_sum / stats->num;
+	mean_l = stats->last_played_sum / stats->num;
+
+	score_n = -((int64_t)afsi->num_played - mean_n)
+		* stats->num_played_correction
+		/ stats->normalization_divisor;
+	score_l = -((int64_t)afsi->last_played - mean_l)
+		* stats->last_played_correction
+		/ stats->normalization_divisor;
+	return (score_n + score_l) / 2;
 }
 
-static int add_afs_statistics(const struct osl_row *row)
+static int add_afs_statistics(const struct osl_row *row,
+		struct afs_statistics *stats)
 {
 	uint64_t n, x, s, q;
 	struct afs_info afsi;
@@ -524,120 +285,100 @@ static int add_afs_statistics(const struct osl_row *row)
 	ret = get_afsi_of_row(row, &afsi);
 	if (ret < 0)
 		return ret;
-	n = statistics.num;
+	n = stats->num;
 	x = afsi.last_played;
-	s = statistics.last_played_sum;
+	s = stats->last_played_sum;
 	if (n > 0) {
 		q = (x > s / n)? x - s / n : s / n - x;
-		statistics.last_played_qd += q * q * n / (n + 1);
+		stats->last_played_qd += q * q * n / (n + 1);
 	}
-	statistics.last_played_sum += x;
+	stats->last_played_sum += x;
 
 	x = afsi.num_played;
-	s = statistics.num_played_sum;
+	s = stats->num_played_sum;
 	if (n > 0) {
 		q = (x > s / n)? x - s / n : s / n - x;
-		statistics.num_played_qd += q * q * n / (n + 1);
+		stats->num_played_qd += q * q * n / (n + 1);
 	}
-	statistics.num_played_sum += x;
-	statistics.num++;
+	stats->num_played_sum += x;
+	stats->num++;
 	return 1;
 }
 
 static int del_afs_statistics(const struct osl_row *row)
 {
+	struct afs_statistics *stats = &current_mood->stats;
 	uint64_t n, s, q, a, new_s;
 	struct afs_info afsi;
 	int ret;
 	ret = get_afsi_of_row(row, &afsi);
 	if (ret < 0)
 		return ret;
-	n = statistics.num;
+	n = stats->num;
 	assert(n);
 	if (n == 1) {
-		memset(&statistics, 0, sizeof(statistics));
+		memset(stats, 0, sizeof(*stats));
+		stats->normalization_divisor = 1;
 		return 1;
 	}
 
-	s = statistics.last_played_sum;
-	q = statistics.last_played_qd;
+	s = stats->last_played_sum;
+	q = stats->last_played_qd;
 	a = afsi.last_played;
 	new_s = s - a;
-	statistics.last_played_sum = new_s;
-	statistics.last_played_qd = q + s * s / n - a * a
+	stats->last_played_sum = new_s;
+	stats->last_played_qd = q + s * s / n - a * a
 		- new_s * new_s / (n - 1);
 
-	s = statistics.num_played_sum;
-	q = statistics.num_played_qd;
+	s = stats->num_played_sum;
+	q = stats->num_played_qd;
 	a = afsi.num_played;
 	new_s = s - a;
-	statistics.num_played_sum = new_s;
-	statistics.num_played_qd = q + s * s / n - a * a
+	stats->num_played_sum = new_s;
+	stats->num_played_qd = q + s * s / n - a * a
 		- new_s * new_s / (n - 1);
 
-	statistics.num--;
+	stats->num--;
 	return 1;
 }
 
 /*
- * At mood open time we determine the set of admissible files for the given
- * mood. The mood score of each admissible file is computed by adding up all
- * mood item scores. Next, we update the afs statistics and append a struct
- * admissible_file_info to a temporary array.
- *
- * When all files have been processed in this way, the final score of each
- * admissible file is computed by adding the dynamic score (which depends on
- * the afs_statistics and the current time) to the mood score. Finally, all
- * audio files in the temporary array are added to the score table and the
- * array is freed.
+ * At mood load time we determine the set of admissible files for the given
+ * mood where each file is identified by a pointer to a row of the audio file
+ * table. In the first pass the pointers are added to a temporary array and
+ * statistics are computed. When all admissible files have been processed in
+ * this way, the score of each admissible file is computed and the (row, score)
+ * pair is added to the score table. This has to be done in a second pass
+ * since the score depends on the statistics. Finally, the array is freed.
  */
-struct admissible_file_info
-{
-	/** The admissible audio file. */
-	struct osl_row *aft_row;
-	/** Its score. */
-	long score;
-};
-
-/** The temporary array of admissible files. */
 struct admissible_array {
 	/** Files are admissible wrt. this mood. */
-	struct mood *m;
+	struct mood_instance *m;
 	/** The size of the array */
 	unsigned size;
 	/** Pointer to the array of admissible files. */
-	struct admissible_file_info *array;
+	struct osl_row **array;
 };
 
-/**
- * Add an entry to the array of admissible files.
- *
- * \param aft_row The audio file to be added.
- * \param private_data Pointer to a struct admissible_file_info.
- *
- * \return 1 if row admissible, 0 if not, negative on errors.
+/*
+ * Check whether the given audio file is admissible. If it is, add it to array
+ * of admissible files.
  */
 static int add_if_admissible(struct osl_row *aft_row, void *data)
 {
 	struct admissible_array *aa = data;
-	int ret;
-	long score = 0;
+	struct afs_statistics *stats = &aa->m->stats;
 
-	ret = row_is_admissible(aft_row, aa->m, &score);
-	if (ret <= 0)
-		return ret;
-	if (statistics.num >= aa->size) {
+	if (!mp_eval_row(aft_row, aa->m->parser_context))
+		return 0;
+	if (stats->num >= aa->size) {
 		aa->size *= 2;
 		aa->size += 100;
-		aa->array = para_realloc(aa->array,
-			aa->size * sizeof(struct admissible_file_info));
+		aa->array = arr_realloc(aa->array, aa->size,
+			sizeof(struct osl_row *));
 	}
-	aa->array[statistics.num].aft_row = aft_row;
-	aa->array[statistics.num].score = score;
-	ret = add_afs_statistics(aft_row);
-	if (ret < 0)
-		return ret;
-	return 1;
+	aa->array[stats->num] = aft_row;
+	return add_afs_statistics(aft_row, stats);
 }
 
 /**
@@ -682,29 +423,25 @@ _static_inline_ int64_t update_quadratic_deviation(int64_t n, int64_t old_qd,
 	return old_qd + delta * (sigma - 2 * old_sum / n - delta / n);
 }
 
-static int update_afs_statistics(struct afs_info *old_afsi,
+static void update_afs_statistics(struct afs_info *old_afsi,
 		struct afs_info *new_afsi)
 {
-	unsigned n;
-	int ret = get_num_admissible_files(&n);
-
-	if (ret < 0)
-		return ret;
-	assert(n);
-
-	statistics.last_played_qd = update_quadratic_deviation(n,
-		statistics.last_played_qd, old_afsi->last_played,
-		new_afsi->last_played, statistics.last_played_sum);
-	statistics.last_played_sum += new_afsi->last_played - old_afsi->last_played;
-
-	statistics.num_played_qd = update_quadratic_deviation(n,
-		statistics.num_played_qd, old_afsi->num_played,
-		new_afsi->num_played, statistics.num_played_sum);
-	statistics.num_played_sum += new_afsi->num_played - old_afsi->num_played;
-	return 1;
+	struct afs_statistics *stats = &current_mood->stats;
+
+	assert(stats->num > 0);
+	stats->last_played_qd = update_quadratic_deviation(stats->num,
+		stats->last_played_qd, old_afsi->last_played,
+		new_afsi->last_played, stats->last_played_sum);
+	stats->last_played_sum += new_afsi->last_played - old_afsi->last_played;
+
+	stats->num_played_qd = update_quadratic_deviation(stats->num,
+		stats->num_played_qd, old_afsi->num_played,
+		new_afsi->num_played, stats->num_played_sum);
+	stats->num_played_sum += new_afsi->num_played - old_afsi->num_played;
 }
 
-static int add_to_score_table(const struct osl_row *aft_row, long mood_score)
+static int add_to_score_table(const struct osl_row *aft_row,
+		struct mood_instance *m)
 {
 	long score;
 	struct afs_info afsi;
@@ -712,8 +449,8 @@ static int add_to_score_table(const struct osl_row *aft_row, long mood_score)
 
 	if (ret < 0)
 		return ret;
-	score = compute_score(&afsi, mood_score);
-	return score_add(aft_row, score);
+	score = compute_score(&afsi, &m->stats);
+	return score_add(aft_row, score, m->score_table);
 }
 
 static int delete_from_statistics_and_score_table(const struct osl_row *aft_row)
@@ -725,23 +462,18 @@ static int delete_from_statistics_and_score_table(const struct osl_row *aft_row)
 }
 
 /**
- * Delete one entry from the statistics and from the score table.
+ * Delete an audio file from the score table and update mood statistics.
  *
- * \param aft_row The audio file which is no longer admissible.
+ * \param aft_row Identifies the row to delete.
  *
- * \return Positive on success, negative on errors.
+ * \return Standard.
  *
  * \sa \ref score_delete().
  */
 static int mood_delete_audio_file(const struct osl_row *aft_row)
 {
-	int ret;
-
-	ret = row_belongs_to_score_table(aft_row, NULL);
-	if (ret < 0)
-		return ret;
-	if (!ret) /* not admissible, nothing to do */
-		return 1;
+	if (!row_belongs_to_score_table(aft_row))
+		return 0;
 	return delete_from_statistics_and_score_table(aft_row);
 }
 
@@ -760,194 +492,225 @@ static int mood_update_audio_file(const struct osl_row *aft_row,
 		struct afs_info *old_afsi)
 {
 	long score, percent;
-	int ret, is_admissible, was_admissible = 0;
+	int ret;
+	bool is_admissible, was_admissible;
 	struct afs_info afsi;
-	unsigned rank;
 
 	if (!current_mood)
 		return 1; /* nothing to do */
-	ret = row_belongs_to_score_table(aft_row, &rank);
-	if (ret < 0)
-		return ret;
-	was_admissible = ret;
-	ret = row_is_admissible(aft_row, current_mood, &score);
-	if (ret < 0)
-		return ret;
-	is_admissible = (ret > 0);
+	was_admissible = row_belongs_to_score_table(aft_row);
+	is_admissible = mp_eval_row(aft_row, current_mood->parser_context);
 	if (!was_admissible && !is_admissible)
 		return 1;
 	if (was_admissible && !is_admissible)
 		return delete_from_statistics_and_score_table(aft_row);
 	if (!was_admissible && is_admissible) {
-		ret = add_afs_statistics(aft_row);
+		ret = add_afs_statistics(aft_row, &current_mood->stats);
 		if (ret < 0)
 			return ret;
-		return add_to_score_table(aft_row, score);
+		return add_to_score_table(aft_row, current_mood);
 	}
 	/* update score */
 	ret = get_afsi_of_row(aft_row, &afsi);
 	if (ret < 0)
 		return ret;
-	if (old_afsi) {
-		ret = update_afs_statistics(old_afsi, &afsi);
-		if (ret < 0)
-			return ret;
-	}
-	score = compute_score(&afsi, score);
+	if (old_afsi)
+		update_afs_statistics(old_afsi, &afsi);
+	score = compute_score(&afsi, &current_mood->stats);
 	PARA_DEBUG_LOG("score: %li\n", score);
 	percent = (score + 100) / 3;
 	if (percent > 100)
 		percent = 100;
 	else if (percent < 0)
 		percent = 0;
-	PARA_DEBUG_LOG("moving from rank %u to %li%%\n", rank, percent);
+	PARA_DEBUG_LOG("moving to %li%%\n", percent);
 	return score_update(aft_row, percent);
 }
 
-static void log_statistics(void)
+/* sse: seconds since epoch. */
+static char *get_statistics(struct mood_instance *m, int64_t sse)
 {
-	unsigned n = statistics.num;
+	unsigned n = m->stats.num;
 	int mean_days, sigma_days;
-	/*
-	 * We can not use the "now" pointer from sched.c here because we are
-	 * called before schedule(), which initializes "now".
-	 */
-	struct timeval rnow;
 
-	assert(current_mood);
-	PARA_NOTICE_LOG("loaded mood %s\n", current_mood->name?
-		current_mood->name : "(dummy)");
-	if (!n) {
-		PARA_WARNING_LOG("no admissible files\n");
-		return;
-	}
-	PARA_NOTICE_LOG("%u admissible files\n", statistics.num);
-	clock_get_realtime(&rnow);
-	mean_days = (rnow.tv_sec - statistics.last_played_sum / n) / 3600 / 24;
-	sigma_days = int_sqrt(statistics.last_played_qd / n) / 3600 / 24;
-	PARA_NOTICE_LOG("last_played mean/sigma: %d/%d days\n", mean_days, sigma_days);
-	PARA_NOTICE_LOG("num_played mean/sigma: %llu/%llu\n",
-		(long long unsigned)statistics.num_played_sum / n,
-		(long long unsigned)int_sqrt(statistics.num_played_qd / n));
+	if (n == 0)
+		return make_message("no admissible files\n");
+	mean_days = (sse - m->stats.last_played_sum / n) / 3600 / 24;
+	sigma_days = int_sqrt(m->stats.last_played_qd / n) / 3600 / 24;
+	return make_message(
+		"loaded mood %s (%u files)\n"
+		"last_played mean/sigma: %d/%d days\n"
+		"num_played mean/sigma: %" PRId64 "/%" PRIu64 "\n"
+		"correction factor ratio: %.2lf\n"
+	,
+		m->name? m->name : "(dummy)",
+		n,
+		mean_days, sigma_days,
+		m->stats.num_played_sum / n,
+		int_sqrt(m->stats.num_played_qd / n),
+		86400.0 * m->stats.last_played_correction /
+			m->stats.num_played_correction
+	);
 }
 
 /**
- * Close the current mood.
+ * Free all resources of a mood instance.
+ *
+ * \param m As obtained by \ref mood_load(). If NULL, unload the current mood.
  *
- * Frees all resources of the current mood.
+ * It's OK to call this with m == NULL even if no current mood is loaded.
  */
-void close_current_mood(void)
+void mood_unload(struct mood_instance *m)
 {
+	if (m)
+		return destroy_mood(m);
 	destroy_mood(current_mood);
 	current_mood = NULL;
-	memset(&statistics, 0, sizeof(statistics));
+}
+
+static void compute_correction_factors(int64_t sse, struct afs_statistics *s)
+{
+	if (s->num > 0) {
+		s->normalization_divisor = int_sqrt(s->last_played_qd)
+			* int_sqrt(s->num_played_qd) / s->num / 100;
+		s->num_played_correction = sse - s->last_played_sum / s->num;
+		s->last_played_correction = s->num_played_sum / s->num;
+	}
+	if (s->num_played_correction == 0)
+		s->num_played_correction = 1;
+	if (s->normalization_divisor == 0)
+		s->normalization_divisor = 1;
+	if (s->last_played_correction == 0)
+		s->last_played_correction = 1;
 }
 
 /**
- * Change the current mood.
+ * Populate a score table with admissible files for the given mood.
  *
- * \param mood_name The name of the mood to open.
- * \param errmsg Error description is returned here.
+ * This consults the mood table to initialize the mood parser with the mood
+ * expression stored in the blob object which corresponds to the given name. A
+ * score table is allocated and populated with references to those entries of
+ * the audio file table which evaluate as admissible with respect to the mood
+ * expression. For each audio file a score value is computed and stored along
+ * with the file reference.
  *
- * If \a mood_name is \a NULL, load the dummy mood that accepts every audio file
- * and uses a scoring method based only on the \a last_played information.
+ * \param mood_name The name of the mood to load.
+ * \param result Opaque, refers to the mood parser and the score table.
+ * \param msg Error message or mood info is returned here.
  *
- * The errmsg pointer may be NULL, in which case no error message will be
- * returned. If a non-NULL pointer is given, the caller must free *errmsg.
+ * If the mood name is NULL, the dummy mood is loaded. This mood regards every
+ * audio file as admissible.
  *
- * If there is already an open mood, it will be closed first.
+ * A NULL result pointer instructs the function to operate on the current mood.
+ * That is, on the mood instance which is used by the server to select the next
+ * audio file for streaming. In this mode of operation, the mood which was
+ * active before the call, if any, is unloaded on success.
  *
- * \return Positive on success, negative on errors.
+ * If result is not NULL, the current mood is unaffected and *result points to
+ * an initialized mood instance on success. The caller can pass this reference
+ * to \ref mood_loop() to iterate over the admissible files, and should call
+ * \ref mood_unload() to free the mood instance afterwards.
+ *
+ * If the message pointer is not NULL, a suitable message is returned there in
+ * all cases. The caller must free this string.
+ *
+ * \return The number of admissible files on success, negative on errors. On
+ * errors, the current mood remains unaffected even if result is NULL. It is
+ * not considered an error if no files are admissible.
  *
- * \sa struct \ref afs_info::last_played, \ref mp_eval_row().
+ * \sa \ref mp_eval_row().
  */
-int change_current_mood(const char *mood_name, char **errmsg)
+int mood_load(const char *mood_name, struct mood_instance **result, char **msg)
 {
 	int i, ret;
-	struct admissible_array aa = {
-		.size = 0,
-		.array = NULL
-	};
+	struct admissible_array aa = {.size = 0};
+	/*
+	 * We can not use the "now" pointer from sched.c here because we are
+	 * called before schedule(), which initializes "now".
+	 */
+	struct timeval rnow;
 
 	if (mood_name) {
-		struct mood *m;
-		struct osl_row *row;
-		struct osl_object obj;
-
-		if (!*mood_name) {
-			*errmsg = make_message("empty mood name");
-			return -ERRNO_TO_PARA_ERROR(EINVAL);
-		}
-		obj.data = (char *)mood_name;
-		obj.size = strlen(mood_name) + 1;
-		ret = osl(osl_get_row(moods_table, BLOBCOL_NAME, &obj, &row));
-		if (ret < 0) {
-			if (errmsg)
-				*errmsg = make_message("no such mood: %s",
-					mood_name);
-			return ret;
-		}
-		ret = load_mood(row, &m, errmsg);
+		ret = init_mood_parser(mood_name, &aa.m, msg);
 		if (ret < 0)
 			return ret;
-		close_current_mood();
-		current_mood = m;
-	} else { /* load dummy mood */
-		close_current_mood();
-		current_mood = alloc_new_mood(NULL);
-	}
-	aa.m = current_mood;
+	} else /* load dummy mood */
+		aa.m = alloc_new_mood(NULL);
 	PARA_NOTICE_LOG("computing statistics of admissible files\n");
 	ret = audio_file_loop(&aa, add_if_admissible);
 	if (ret < 0) {
-		if (errmsg)
-			*errmsg = make_message("audio file loop failed");
+		if (msg) /* false if we are called via the event handler */
+			*msg = make_message("audio file loop failed\n");
 		goto out;
 	}
-	for (i = 0; i < statistics.num; i++) {
-		struct admissible_file_info *a = aa.array + i;
-		ret = add_to_score_table(a->aft_row, a->score);
+	clock_get_realtime(&rnow);
+	compute_correction_factors(rnow.tv_sec, &aa.m->stats);
+	if (result)
+		score_open(&aa.m->score_table);
+	for (i = 0; i < aa.m->stats.num; i++) {
+		ret = add_to_score_table(aa.array[i], aa.m);
 		if (ret < 0) {
-			if (errmsg)
-				*errmsg = make_message(
-					"could not add row to score table");
+			if (msg)
+				*msg = make_message(
+					"could not add row to score table\n");
 			goto out;
 		}
 	}
-	log_statistics();
-	ret = statistics.num;
+	/* success */
+	if (msg)
+		*msg = get_statistics(aa.m, rnow.tv_sec);
+	ret = aa.m->stats.num;
+	if (result)
+		*result = aa.m;
+	else {
+		mood_unload(NULL);
+		current_mood = aa.m;
+	}
+	ret = 1;
 out:
 	free(aa.array);
-	if (ret < 0)
-		close_current_mood();
+	if (ret <= 0) /* error, or no admissible files */
+		destroy_mood(aa.m);
 	return ret;
 }
 
-/*
- * Close and re-open the current mood.
+/**
+ * Iterate over the admissible files of a mood instance.
+ *
+ * This wrapper around \ref score_loop() is the mood counterpart of \ref
+ * playlist_loop().
  *
- * This function is called on events which render the current list of
- * admissible files useless, for example if an attribute is removed from the
- * attribute table.
+ * \param m Determines the score table to iterate. Must not be NULL.
+ * \param func See \ref score_loop().
+ * \param data See \ref score_loop().
  *
- * If no mood is currently open, the function returns success.
+ * \return See \ref score_loop(), \ref playlist_loop().
+ */
+int mood_loop(struct mood_instance *m, osl_rbtree_loop_func *func, void *data)
+{
+	return score_loop(func, m->score_table, data);
+}
+
+/*
+ * Empty the score table and start over.
+ *
+ * This function is called on events which render the current set of admissible
+ * files invalid, for example if an attribute is removed from the attribute
+ * table.
  */
 static int reload_current_mood(void)
 {
 	int ret;
 	char *mood_name = NULL;
 
-	ret = clear_score_table();
-	if (ret < 0)
-		return ret;
-	if (!current_mood)
-		return 1;
+	assert(current_mood);
+	score_clear();
 	PARA_NOTICE_LOG("reloading %s\n", current_mood->name?
 		current_mood->name : "(dummy)");
 	if (current_mood->name)
 		mood_name = para_strdup(current_mood->name);
-	close_current_mood();
-	ret = change_current_mood(mood_name, NULL);
+	mood_unload(NULL);
+	ret = mood_load(mood_name, NULL, NULL);
 	free(mood_name);
 	return ret;
 }
@@ -959,9 +722,17 @@ static int reload_current_mood(void)
  * \param pb Unused.
  * \param data Its type depends on the event.
  *
- * This function performs actions required due to the occurrence of the given
- * event. Possible actions include reload of the current mood and update of the
- * score of an audio file.
+ * This function updates the score table according to the event that has
+ * occurred. Two actions are possible: (a) reload the current mood, or (b)
+ * add/remove/update the row of the score table which corresponds to the audio
+ * file that has been modified or whose afs info has been changed. It depends
+ * on the type of the event which action (if any) is performed.
+ *
+ * The callbacks of command handlers such as com_add() or com_touch() which
+ * modify the audio file table call this function. The virtual streaming system
+ * also calls this after it has updated the afs info of the file it is about to
+ * stream (the one with the highest score). If the file stays admissible, its
+ * score is recomputed so that a different file is picked next time.
  *
  * \return Standard.
  */