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Linux build fix
[disorder] / server / choose.c
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1/*
2 * This file is part of DisOrder
3 * Copyright (C) 2008 Richard Kettlewell
fd9000bc 4 * Copyright (C) 2008 Mark Wooding
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5 *
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 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
19 * USA
20 */
21/** @file choose.c
22 * @brief Random track chooser
23 *
24 * Picks a track at random and writes it to standard output. If for
25 * any reason no track can be picked - even a trivial reason like a
26 * deadlock - it just exits and expects the server to try again.
27 */
28
05b75f8d 29#include "disorder-server.h"
bea6f6d5 30
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31#define BASE_WEIGHT 90000
32
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33static DB_TXN *global_tid;
34
35static const struct option options[] = {
36 { "help", no_argument, 0, 'h' },
37 { "version", no_argument, 0, 'V' },
38 { "config", required_argument, 0, 'c' },
39 { "debug", no_argument, 0, 'd' },
40 { "no-debug", no_argument, 0, 'D' },
41 { "syslog", no_argument, 0, 's' },
42 { "no-syslog", no_argument, 0, 'S' },
43 { 0, 0, 0, 0 }
44};
45
46/* display usage message and terminate */
47static void help(void) {
48 xprintf("Usage:\n"
49 " disorder-choose [OPTIONS]\n"
50 "Options:\n"
51 " --help, -h Display usage message\n"
52 " --version, -V Display version number\n"
53 " --config PATH, -c PATH Set configuration file\n"
54 " --debug, -d Turn on debugging\n"
55 " --[no-]syslog Enable/disable logging to syslog\n"
56 "\n"
57 "Track choose for DisOrder. Not intended to be run\n"
58 "directly.\n");
59 xfclose(stdout);
60 exit(0);
61}
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62/** @brief Sum of all weights */
63static unsigned long long total_weight;
64
74b1f70d 65/** @brief The winning track */
66static const char *winning = 0;
67
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68/** @brief Count of tracks */
69static long ntracks;
70
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71static char **required_tags;
72static char **prohibited_tags;
73
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74static int queue_contains(const struct queue_entry *head,
75 const char *track) {
76 const struct queue_entry *q;
77
78 for(q = head->next; q != head; q = q->next)
79 if(!strcmp(q->track, track))
80 return 1;
81 return 0;
82}
83
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84/** @brief Compute the weight of a track
85 * @param track Track name (UTF-8)
86 * @param data Track data
87 * @param prefs Track preferences
88 * @return Track weight (non-negative)
89 *
90 * Tracks to be excluded entirely are given a weight of 0.
91 */
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92static unsigned long compute_weight(const char *track,
93 struct kvp *data,
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94 struct kvp *prefs) {
95 const char *s;
91c9324a 96 char **track_tags;
05dcfac6 97 time_t last, now = time(0);
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98
99 /* Reject tracks not in any collection (race between edit config and
100 * rescan) */
101 if(!find_track_root(track)) {
102 info("found track not in any collection: %s", track);
103 return 0;
104 }
bea6f6d5 105
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106 /* Reject aliases to avoid giving aliased tracks extra weight */
107 if(kvp_get(data, "_alias_for"))
108 return 0;
109
110 /* Reject tracks with random play disabled */
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111 if((s = kvp_get(prefs, "pick_at_random"))
112 && !strcmp(s, "0"))
113 return 0;
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114
115 /* Reject tracks played within the last 8 hours */
116 if((s = kvp_get(prefs, "played_time"))) {
117 last = atoll(s);
cebe3127 118 if(now < last + config->replay_min)
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119 return 0;
120 }
121
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122 /* Reject tracks currently in the queue or in the recent list */
123 if(queue_contains(&qhead, track)
124 || queue_contains(&phead, track))
125 return 0;
126
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127 /* We'll need tags for a number of things */
128 track_tags = parsetags(kvp_get(prefs, "tags"));
129
130 /* Reject tracks with prohibited tags */
131 if(prohibited_tags && tag_intersection(track_tags, prohibited_tags))
132 return 0;
133
134 /* Reject tracks that lack required tags */
135 if(*required_tags && !tag_intersection(track_tags, required_tags))
136 return 0;
137
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138 /* Use the configured weight if available */
139 if((s = kvp_get(prefs, "weight"))) {
140 long n;
141 errno = 0;
142
143 n = strtol(s, 0, 10);
144 if((errno == 0 || errno == ERANGE) && n >= 0)
145 return n;
146 }
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147
148 /* Bias up tracks that were recently added */
149 if((s = kvp_get(data, "_noticed"))) {
150 const time_t noticed = atoll(s);
151
152 if(noticed + config->new_bias_age < now)
153 /* Currently we just step up the weight of tracks that are in range. A
154 * more sophisticated approach would be to linearly decay from new_bias
155 * down to BASE_WEIGHT over the course of the new_bias_age interval
156 * starting when the track is added. */
157 return config->new_bias;
158 }
36a1a882 159
05dcfac6 160 return BASE_WEIGHT;
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161}
162
4005a0d6 163/** @brief Pick a random integer uniformly from [0, limit) */
164static unsigned long long pick_weight(unsigned long long limit) {
165 unsigned char buf[(sizeof(unsigned long long) * CHAR_BIT + 7)/8], m;
166 unsigned long long t, r, slop;
167 int i, nby, nbi;
168
026a72d4 169 D(("pick_weight: limit = %#016llx", limit));
4005a0d6 170
171 /* First, decide how many bits of output we actually need; do bytes first
172 * (they're quicker) and then bits.
173 *
174 * To speed this up, we could use a binary search if we knew where to
175 * start. (Note that shifting by ULLONG_BITS or more (if such a constant
176 * existed) is undefined behaviour, so we mustn't do that.) Figuring out a
177 * start point involves preprocessor and/or autoconf magic.
178 */
179 for (nby = 1, t = (limit - 1) >> 8; t; nby++, t >>= 8)
180 ;
181 nbi = (nby - 1) << 3; t = limit >> nbi;
182 if (t >> 4) { t >>= 4; nbi += 4; }
183 if (t >> 2) { t >>= 2; nbi += 2; }
184 if (t >> 1) { t >>= 1; nbi += 1; }
185 nbi++;
026a72d4 186 D(("nby = %d; nbi = %d", nby, nbi));
4005a0d6 187
188 /* Main randomness collection loop. We read a number of bytes from the
189 * randomness source, and glue them together into an integer (dropping
190 * bits off the top byte as necessary). Call the result r; we have
191 * 2^{nbi - 1) <= limit < 2^nbi and r < 2^nbi. If r < limit then we win;
192 * otherwise we try again. Given the above bounds, we expect fewer than 2
193 * iterations.
194 *
195 * Unfortunately there are subtleties. In particular, 2^nbi may in fact be
196 * zero due to overflow. So in fact what we do is compute slop = 2^nbi -
197 * limit > 0; if r < slop then we try again, otherwise r - slop is our
198 * winner.
199 */
026a72d4 200 slop = ((unsigned long long)2 << (nbi - 1)) - limit;
4005a0d6 201 m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff;
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202 D(("slop = %#016llx", slop));
203 D(("m = 0x%02x", m));
4005a0d6 204
205 do {
206 /* Actually get some random data. */
fcdff139 207 random_get(buf, nby);
4005a0d6 208
209 /* Clobber the top byte. */
210 buf[0] &= m;
211
212 /* Turn it into an integer. */
213 for (r = 0, i = 0; i < nby; i++)
214 r = (r << 8) | buf[i];
026a72d4 215 D(("r = %#016llx", r));
4005a0d6 216 } while (r < slop);
217
026a72d4 218 D((" result=%#016llx", r - slop));
4005a0d6 219 return r - slop;
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220}
221
74b1f70d 222/** @brief Called for each track */
223static int collect_tracks_callback(const char *track,
224 struct kvp *data,
225 struct kvp *prefs,
226 void attribute((unused)) *u,
227 DB_TXN attribute((unused)) *tid) {
228 unsigned long weight = compute_weight(track, data, prefs);
bea6f6d5 229
74b1f70d 230 /* Decide whether this is the winning track.
231 *
232 * Suppose that we have n things, and thing i, for 0 <= i < n, has weight
233 * w_i. Let c_i = w_0 + ... + w_{i-1} be the cumulative weight of the
234 * things previous to thing i, and let W = c_n = w_0 + ... + w_{i-1} be the
235 * total weight. We can clearly choose a random thing with the correct
236 * weightings by picking a random number r in [0, W) and chooeing thing i
237 * where c_i <= r < c_i + w_i. But this involves having an enormous list
238 * and taking two passes over it (which has bad locality and is ugly).
239 *
240 * Here's another way. Initialize v = -1. Examine the things in order;
241 * for thing i, choose a random number r_i in [0, c_i + w_i). If r_i < w_i
242 * then set v <- i.
243 *
244 * Claim. For all 0 <= i < n, the above algorithm chooses thing i with
245 * probability w_i/W.
246 *
247 * Proof. Induction on n. The claim is clear for n = 1. Suppose it's
248 * true for n - 1. Let L be the event that we choose thing n - 1. Clearly
249 * Pr[L] = w_{n-1}/W. Condition on not-L: then the probabilty that we
250 * choose thing i, for 0 <= i < n - 1, is w_i/c_{n-1} (induction
251 * hypothesis); undoing the conditioning gives the desired result.
252 */
026a72d4 253 D(("consider %s", track));
74b1f70d 254 if(weight) {
255 total_weight += weight;
256 if (pick_weight(total_weight) < weight)
257 winning = track;
bea6f6d5 258 }
74b1f70d 259 ntracks++;
260 return 0;
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261}
262
263int main(int argc, char **argv) {
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264 int n, logsyslog = !isatty(2), err;
265 const char *tags;
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266
267 set_progname(argv);
268 mem_init();
269 if(!setlocale(LC_CTYPE, "")) fatal(errno, "error calling setlocale");
270 while((n = getopt_long(argc, argv, "hVc:dDSs", options, 0)) >= 0) {
271 switch(n) {
272 case 'h': help();
273 case 'V': version("disorder-choose");
274 case 'c': configfile = optarg; break;
275 case 'd': debugging = 1; break;
276 case 'D': debugging = 0; break;
277 case 'S': logsyslog = 0; break;
278 case 's': logsyslog = 1; break;
279 default: fatal(0, "invalid option");
280 }
281 }
282 if(logsyslog) {
283 openlog(progname, LOG_PID, LOG_DAEMON);
284 log_default = &log_syslog;
285 }
286 if(config_read(0)) fatal(0, "cannot read configuration");
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287 /* Find out current queue/recent list */
288 queue_read();
289 recent_read();
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290 /* Generate the candidate track list */
291 trackdb_init(TRACKDB_NO_RECOVER);
292 trackdb_open(TRACKDB_NO_UPGRADE|TRACKDB_READ_ONLY);
293 global_tid = trackdb_begin_transaction();
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294 if((err = trackdb_get_global_tid("required-tags", global_tid, &tags)))
295 fatal(0, "error getting required-tags: %s", db_strerror(err));
296 required_tags = parsetags(tags);
297 if((err = trackdb_get_global_tid("prohibited-tags", global_tid, &tags)))
298 fatal(0, "error getting prohibited-tags: %s", db_strerror(err));
299 prohibited_tags = parsetags(tags);
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300 if(trackdb_scan(0, collect_tracks_callback, 0, global_tid))
301 exit(1);
302 trackdb_commit_transaction(global_tid);
303 trackdb_close();
304 trackdb_deinit();
026a72d4 305 D(("ntracks=%ld total_weight=%lld", ntracks, total_weight));
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306 if(!total_weight)
307 fatal(0, "no tracks match random choice criteria");
74b1f70d 308 if(!winning)
309 fatal(0, "internal: failed to pick a track");
bea6f6d5 310 /* Pick a track */
74b1f70d 311 xprintf("%s", winning);
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312 xfclose(stdout);
313 return 0;
314}
315
316/*
317Local Variables:
318c-basic-offset:2
319comment-column:40
320fill-column:79
321indent-tabs-mode:nil
322End:
323*/