2 * This file is part of DisOrder
3 * Copyright (C) 2008 Richard Kettlewell
4 * Copyright (C) 2008 Mark Wooding
6 * This program is free software: you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation, either version 3 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
19 /** @file server/choose.c
20 * @brief Random track chooser
22 * Picks a track at random and writes it to standard output. If for
23 * any reason no track can be picked - even a trivial reason like a
24 * deadlock - it just exits and expects the server to try again.
27 #include "disorder-server.h"
29 #define BASE_WEIGHT 90000
31 static DB_TXN
*global_tid
;
33 static const struct option options
[] = {
34 { "help", no_argument
, 0, 'h' },
35 { "version", no_argument
, 0, 'V' },
36 { "config", required_argument
, 0, 'c' },
37 { "debug", no_argument
, 0, 'd' },
38 { "no-debug", no_argument
, 0, 'D' },
39 { "syslog", no_argument
, 0, 's' },
40 { "no-syslog", no_argument
, 0, 'S' },
44 /* display usage message and terminate */
45 static void help(void) {
47 " disorder-choose [OPTIONS]\n"
49 " --help, -h Display usage message\n"
50 " --version, -V Display version number\n"
51 " --config PATH, -c PATH Set configuration file\n"
52 " --debug, -d Turn on debugging\n"
53 " --[no-]syslog Enable/disable logging to syslog\n"
55 "Track chooser for DisOrder. Not intended to be run\n"
60 /** @brief Sum of all weights */
61 static unsigned long long total_weight
;
63 /** @brief The winning track */
64 static const char *winning
= 0;
66 /** @brief Count of tracks */
69 static char **required_tags
;
70 static char **prohibited_tags
;
72 static int queue_contains(const struct queue_entry
*head
,
74 const struct queue_entry
*q
;
76 for(q
= head
->next
; q
!= head
; q
= q
->next
)
77 if(!strcmp(q
->track
, track
))
82 /** @brief Compute the weight of a track
83 * @param track Track name (UTF-8)
84 * @param data Track data
85 * @param prefs Track preferences
86 * @return Track weight (non-negative)
88 * Tracks to be excluded entirely are given a weight of 0.
90 static unsigned long compute_weight(const char *track
,
95 time_t last
, now
= time(0);
97 /* Reject tracks not in any collection (race between edit config and
99 if(!find_track_root(track
)) {
100 info("found track not in any collection: %s", track
);
104 /* Reject aliases to avoid giving aliased tracks extra weight */
105 if(kvp_get(data
, "_alias_for"))
108 /* Reject tracks with random play disabled */
109 if((s
= kvp_get(prefs
, "pick_at_random"))
113 /* Reject tracks played within the last 8 hours */
114 if((s
= kvp_get(prefs
, "played_time"))) {
116 if(now
< last
+ config
->replay_min
)
120 /* Reject tracks currently in the queue or in the recent list */
121 if(queue_contains(&qhead
, track
)
122 || queue_contains(&phead
, track
))
125 /* We'll need tags for a number of things */
126 track_tags
= parsetags(kvp_get(prefs
, "tags"));
128 /* Reject tracks with prohibited tags */
129 if(prohibited_tags
&& tag_intersection(track_tags
, prohibited_tags
))
132 /* Reject tracks that lack required tags */
133 if(*required_tags
&& !tag_intersection(track_tags
, required_tags
))
136 /* Use the configured weight if available */
137 if((s
= kvp_get(prefs
, "weight"))) {
141 n
= strtol(s
, 0, 10);
142 if((errno
== 0 || errno
== ERANGE
) && n
>= 0)
146 /* Bias up tracks that were recently added */
147 if((s
= kvp_get(data
, "_noticed"))) {
148 const time_t noticed
= atoll(s
);
150 if(noticed
+ config
->new_bias_age
< now
)
151 /* Currently we just step up the weight of tracks that are in range. A
152 * more sophisticated approach would be to linearly decay from new_bias
153 * down to BASE_WEIGHT over the course of the new_bias_age interval
154 * starting when the track is added. */
155 return config
->new_bias
;
161 /** @brief Pick a random integer uniformly from [0, limit) */
162 static unsigned long long pick_weight(unsigned long long limit
) {
163 unsigned char buf
[(sizeof(unsigned long long) * CHAR_BIT
+ 7)/8], m
;
164 unsigned long long t
, r
, slop
;
167 D(("pick_weight: limit = %#016llx", limit
));
169 /* First, decide how many bits of output we actually need; do bytes first
170 * (they're quicker) and then bits.
172 * To speed this up, we could use a binary search if we knew where to
173 * start. (Note that shifting by ULLONG_BITS or more (if such a constant
174 * existed) is undefined behaviour, so we mustn't do that.) Figuring out a
175 * start point involves preprocessor and/or autoconf magic.
177 for (nby
= 1, t
= (limit
- 1) >> 8; t
; nby
++, t
>>= 8)
179 nbi
= (nby
- 1) << 3; t
= limit
>> nbi
;
180 if (t
>> 4) { t
>>= 4; nbi
+= 4; }
181 if (t
>> 2) { t
>>= 2; nbi
+= 2; }
182 if (t
>> 1) { t
>>= 1; nbi
+= 1; }
184 D(("nby = %d; nbi = %d", nby
, nbi
));
186 /* Main randomness collection loop. We read a number of bytes from the
187 * randomness source, and glue them together into an integer (dropping
188 * bits off the top byte as necessary). Call the result r; we have
189 * 2^{nbi - 1) <= limit < 2^nbi and r < 2^nbi. If r < limit then we win;
190 * otherwise we try again. Given the above bounds, we expect fewer than 2
193 * Unfortunately there are subtleties. In particular, 2^nbi may in fact be
194 * zero due to overflow. So in fact what we do is compute slop = 2^nbi -
195 * limit > 0; if r < slop then we try again, otherwise r - slop is our
198 slop
= ((unsigned long long)2 << (nbi
- 1)) - limit
;
199 m
= nbi
& 7 ?
(1 << (nbi
& 7)) - 1 : 0xff;
200 D(("slop = %#016llx", slop
));
201 D(("m = 0x%02x", m
));
204 /* Actually get some random data. */
205 random_get(buf
, nby
);
207 /* Clobber the top byte. */
210 /* Turn it into an integer. */
211 for (r
= 0, i
= 0; i
< nby
; i
++)
212 r
= (r
<< 8) | buf
[i
];
213 D(("r = %#016llx", r
));
216 D((" result=%#016llx", r
- slop
));
220 /** @brief Called for each track */
221 static int collect_tracks_callback(const char *track
,
224 void attribute((unused
)) *u
,
225 DB_TXN
attribute((unused
)) *tid
) {
226 unsigned long weight
= compute_weight(track
, data
, prefs
);
228 /* Decide whether this is the winning track.
230 * Suppose that we have n things, and thing i, for 0 <= i < n, has weight
231 * w_i. Let c_i = w_0 + ... + w_{i-1} be the cumulative weight of the
232 * things previous to thing i, and let W = c_n = w_0 + ... + w_{i-1} be the
233 * total weight. We can clearly choose a random thing with the correct
234 * weightings by picking a random number r in [0, W) and chooeing thing i
235 * where c_i <= r < c_i + w_i. But this involves having an enormous list
236 * and taking two passes over it (which has bad locality and is ugly).
238 * Here's another way. Initialize v = -1. Examine the things in order;
239 * for thing i, choose a random number r_i in [0, c_i + w_i). If r_i < w_i
242 * Claim. For all 0 <= i < n, the above algorithm chooses thing i with
245 * Proof. Induction on n. The claim is clear for n = 1. Suppose it's
246 * true for n - 1. Let L be the event that we choose thing n - 1. Clearly
247 * Pr[L] = w_{n-1}/W. Condition on not-L: then the probabilty that we
248 * choose thing i, for 0 <= i < n - 1, is w_i/c_{n-1} (induction
249 * hypothesis); undoing the conditioning gives the desired result.
251 D(("consider %s", track
));
253 total_weight
+= weight
;
254 if (pick_weight(total_weight
) < weight
)
261 int main(int argc
, char **argv
) {
262 int n
, logsyslog
= !isatty(2), err
;
267 if(!setlocale(LC_CTYPE
, "")) fatal(errno
, "error calling setlocale");
268 while((n
= getopt_long(argc
, argv
, "hVc:dDSs", options
, 0)) >= 0) {
271 case 'V': version("disorder-choose");
272 case 'c': configfile
= optarg
; break;
273 case 'd': debugging
= 1; break;
274 case 'D': debugging
= 0; break;
275 case 'S': logsyslog
= 0; break;
276 case 's': logsyslog
= 1; break;
277 default: fatal(0, "invalid option");
281 openlog(progname
, LOG_PID
, LOG_DAEMON
);
282 log_default
= &log_syslog
;
284 if(config_read(0)) fatal(0, "cannot read configuration");
285 /* Find out current queue/recent list */
288 /* Generate the candidate track list */
289 trackdb_init(TRACKDB_NO_RECOVER
);
290 trackdb_open(TRACKDB_NO_UPGRADE
|TRACKDB_READ_ONLY
);
291 global_tid
= trackdb_begin_transaction();
292 if((err
= trackdb_get_global_tid("required-tags", global_tid
, &tags
)))
293 fatal(0, "error getting required-tags: %s", db_strerror(err
));
294 required_tags
= parsetags(tags
);
295 if((err
= trackdb_get_global_tid("prohibited-tags", global_tid
, &tags
)))
296 fatal(0, "error getting prohibited-tags: %s", db_strerror(err
));
297 prohibited_tags
= parsetags(tags
);
298 if(trackdb_scan(0, collect_tracks_callback
, 0, global_tid
)) {
299 global_tid
->abort(global_tid
);
302 trackdb_commit_transaction(global_tid
);
305 D(("ntracks=%ld total_weight=%lld", ntracks
, total_weight
));
307 fatal(0, "no tracks match random choice criteria");
309 fatal(0, "internal: failed to pick a track");
311 xprintf("%s", winning
);