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[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
bea6f6d5 5 *
e7eb3a27 6 * This program is free software: you can redistribute it and/or modify
bea6f6d5 7 * it under the terms of the GNU General Public License as published by
e7eb3a27 8 * the Free Software Foundation, either version 3 of the License, or
bea6f6d5 9 * (at your option) any later version.
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10 *
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.
15 *
bea6f6d5 16 * You should have received a copy of the GNU General Public License
e7eb3a27 17 * along with this program. If not, see <http://www.gnu.org/licenses/>.
bea6f6d5 18 */
59cf25c4 19/** @file server/choose.c
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20 * @brief Random track chooser
21 *
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.
25 */
26
05b75f8d 27#include "disorder-server.h"
bea6f6d5 28
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29#define BASE_WEIGHT 90000
30
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31static DB_TXN *global_tid;
32
33static 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' },
41 { 0, 0, 0, 0 }
42};
43
44/* display usage message and terminate */
45static void help(void) {
46 xprintf("Usage:\n"
47 " disorder-choose [OPTIONS]\n"
48 "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"
54 "\n"
1c6e0e45 55 "Track chooser for DisOrder. Not intended to be run\n"
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56 "directly.\n");
57 xfclose(stdout);
58 exit(0);
59}
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60/** @brief Sum of all weights */
61static unsigned long long total_weight;
62
74b1f70d 63/** @brief The winning track */
64static const char *winning = 0;
65
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66/** @brief Count of tracks */
67static long ntracks;
68
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69static char **required_tags;
70static char **prohibited_tags;
71
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72static int queue_contains(const struct queue_entry *head,
73 const char *track) {
74 const struct queue_entry *q;
75
76 for(q = head->next; q != head; q = q->next)
77 if(!strcmp(q->track, track))
78 return 1;
79 return 0;
80}
81
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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)
87 *
88 * Tracks to be excluded entirely are given a weight of 0.
89 */
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90static unsigned long compute_weight(const char *track,
91 struct kvp *data,
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92 struct kvp *prefs) {
93 const char *s;
91c9324a 94 char **track_tags;
05dcfac6 95 time_t last, now = time(0);
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96
97 /* Reject tracks not in any collection (race between edit config and
98 * rescan) */
99 if(!find_track_root(track)) {
100 info("found track not in any collection: %s", track);
101 return 0;
102 }
bea6f6d5 103
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104 /* Reject aliases to avoid giving aliased tracks extra weight */
105 if(kvp_get(data, "_alias_for"))
106 return 0;
107
108 /* Reject tracks with random play disabled */
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109 if((s = kvp_get(prefs, "pick_at_random"))
110 && !strcmp(s, "0"))
111 return 0;
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112
113 /* Reject tracks played within the last 8 hours */
114 if((s = kvp_get(prefs, "played_time"))) {
115 last = atoll(s);
cebe3127 116 if(now < last + config->replay_min)
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117 return 0;
118 }
119
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120 /* Reject tracks currently in the queue or in the recent list */
121 if(queue_contains(&qhead, track)
122 || queue_contains(&phead, track))
123 return 0;
124
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125 /* We'll need tags for a number of things */
126 track_tags = parsetags(kvp_get(prefs, "tags"));
127
128 /* Reject tracks with prohibited tags */
129 if(prohibited_tags && tag_intersection(track_tags, prohibited_tags))
130 return 0;
131
132 /* Reject tracks that lack required tags */
133 if(*required_tags && !tag_intersection(track_tags, required_tags))
134 return 0;
135
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136 /* Use the configured weight if available */
137 if((s = kvp_get(prefs, "weight"))) {
138 long n;
139 errno = 0;
140
141 n = strtol(s, 0, 10);
142 if((errno == 0 || errno == ERANGE) && n >= 0)
143 return n;
144 }
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145
146 /* Bias up tracks that were recently added */
147 if((s = kvp_get(data, "_noticed"))) {
148 const time_t noticed = atoll(s);
149
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;
156 }
36a1a882 157
05dcfac6 158 return BASE_WEIGHT;
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159}
160
4005a0d6 161/** @brief Pick a random integer uniformly from [0, limit) */
162static 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;
165 int i, nby, nbi;
166
026a72d4 167 D(("pick_weight: limit = %#016llx", limit));
4005a0d6 168
169 /* First, decide how many bits of output we actually need; do bytes first
170 * (they're quicker) and then bits.
171 *
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.
176 */
177 for (nby = 1, t = (limit - 1) >> 8; t; nby++, t >>= 8)
178 ;
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; }
183 nbi++;
026a72d4 184 D(("nby = %d; nbi = %d", nby, nbi));
4005a0d6 185
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
191 * iterations.
192 *
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
196 * winner.
197 */
026a72d4 198 slop = ((unsigned long long)2 << (nbi - 1)) - limit;
4005a0d6 199 m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff;
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200 D(("slop = %#016llx", slop));
201 D(("m = 0x%02x", m));
4005a0d6 202
203 do {
204 /* Actually get some random data. */
fcdff139 205 random_get(buf, nby);
4005a0d6 206
207 /* Clobber the top byte. */
208 buf[0] &= m;
209
210 /* Turn it into an integer. */
211 for (r = 0, i = 0; i < nby; i++)
212 r = (r << 8) | buf[i];
026a72d4 213 D(("r = %#016llx", r));
4005a0d6 214 } while (r < slop);
215
026a72d4 216 D((" result=%#016llx", r - slop));
4005a0d6 217 return r - slop;
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218}
219
74b1f70d 220/** @brief Called for each track */
221static int collect_tracks_callback(const char *track,
222 struct kvp *data,
223 struct kvp *prefs,
224 void attribute((unused)) *u,
225 DB_TXN attribute((unused)) *tid) {
226 unsigned long weight = compute_weight(track, data, prefs);
bea6f6d5 227
74b1f70d 228 /* Decide whether this is the winning track.
229 *
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).
237 *
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
240 * then set v <- i.
241 *
242 * Claim. For all 0 <= i < n, the above algorithm chooses thing i with
243 * probability w_i/W.
244 *
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.
250 */
026a72d4 251 D(("consider %s", track));
74b1f70d 252 if(weight) {
253 total_weight += weight;
254 if (pick_weight(total_weight) < weight)
255 winning = track;
bea6f6d5 256 }
74b1f70d 257 ntracks++;
258 return 0;
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259}
260
261int main(int argc, char **argv) {
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262 int n, logsyslog = !isatty(2), err;
263 const char *tags;
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264
265 set_progname(argv);
266 mem_init();
267 if(!setlocale(LC_CTYPE, "")) fatal(errno, "error calling setlocale");
268 while((n = getopt_long(argc, argv, "hVc:dDSs", options, 0)) >= 0) {
269 switch(n) {
270 case 'h': help();
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");
278 }
279 }
280 if(logsyslog) {
281 openlog(progname, LOG_PID, LOG_DAEMON);
282 log_default = &log_syslog;
283 }
284 if(config_read(0)) fatal(0, "cannot read configuration");
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285 /* Find out current queue/recent list */
286 queue_read();
287 recent_read();
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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();
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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);
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298 if(trackdb_scan(0, collect_tracks_callback, 0, global_tid)) {
299 global_tid->abort(global_tid);
bea6f6d5 300 exit(1);
1dc0ceda 301 }
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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*/