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 2 of the License, or
9 * (at your option) any later version.
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.
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
22 * @brief Random track chooser
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.
38 #include <sys/types.h>
46 #include "configuration.h"
54 #include "trackdb-int.h"
56 #include "trackname.h"
58 #include "server-queue.h"
60 static DB_TXN *global_tid;
62 static const struct option options[] = {
63 { "help", no_argument, 0, 'h' },
64 { "version", no_argument, 0, 'V' },
65 { "config", required_argument, 0, 'c' },
66 { "debug", no_argument, 0, 'd' },
67 { "no-debug", no_argument, 0, 'D' },
68 { "syslog", no_argument, 0, 's' },
69 { "no-syslog", no_argument, 0, 'S' },
73 /* display usage message and terminate */
74 static void help(void) {
76 " disorder-choose [OPTIONS]\n"
78 " --help, -h Display usage message\n"
79 " --version, -V Display version number\n"
80 " --config PATH, -c PATH Set configuration file\n"
81 " --debug, -d Turn on debugging\n"
82 " --[no-]syslog Enable/disable logging to syslog\n"
84 "Track choose for DisOrder. Not intended to be run\n"
89 /** @brief Sum of all weights */
90 static unsigned long long total_weight;
92 /** @brief The winning track */
93 static const char *winning = 0;
95 /** @brief Count of tracks */
98 static char **required_tags;
99 static char **prohibited_tags;
101 static int queue_contains(const struct queue_entry *head,
103 const struct queue_entry *q;
105 for(q = head->next; q != head; q = q->next)
106 if(!strcmp(q->track, track))
111 /** @brief Compute the weight of a track
112 * @param track Track name (UTF-8)
113 * @param data Track data
114 * @param prefs Track preferences
115 * @return Track weight (non-negative)
117 * Tracks to be excluded entirely are given a weight of 0.
119 static unsigned long compute_weight(const char *track,
126 /* Reject tracks not in any collection (race between edit config and
128 if(!find_track_root(track)) {
129 info("found track not in any collection: %s", track);
133 /* Reject aliases to avoid giving aliased tracks extra weight */
134 if(kvp_get(data, "_alias_for"))
137 /* Reject tracks with random play disabled */
138 if((s = kvp_get(prefs, "pick_at_random"))
142 /* Reject tracks played within the last 8 hours */
143 if((s = kvp_get(prefs, "played_time"))) {
146 if(now < last + config->replay_min)
150 /* Reject tracks currently in the queue or in the recent list */
151 if(queue_contains(&qhead, track)
152 || queue_contains(&phead, track))
155 /* We'll need tags for a number of things */
156 track_tags = parsetags(kvp_get(prefs, "tags"));
158 /* Reject tracks with prohibited tags */
159 if(prohibited_tags && tag_intersection(track_tags, prohibited_tags))
162 /* Reject tracks that lack required tags */
163 if(*required_tags && !tag_intersection(track_tags, required_tags))
166 /* Use the configured weight if available */
167 if((s = kvp_get(prefs, "weight"))) {
171 n = strtol(s, 0, 10);
172 if((errno == 0 || errno == ERANGE) && n >= 0)
179 static unsigned char random_buffer[4096];
180 static size_t random_left;
182 /** @brief Fill [buf, buf+n) with random bytes */
183 static void random_bytes(unsigned char *buf, size_t n) {
185 if(random_left > 0) {
186 const size_t this_time = n > random_left ? random_left : n;
188 memcpy(buf, random_buffer + random_left - this_time, this_time);
190 random_left -= this_time;
196 if((fd = open("/dev/urandom", O_RDONLY)) < 0)
197 fatal(errno, "opening /dev/urandom");
199 if((r = read(fd, random_buffer, sizeof random_buffer)) < 0)
200 fatal(errno, "reading /dev/urandom");
201 if((size_t)r < sizeof random_buffer)
202 fatal(0, "short read from /dev/urandom");
203 random_left = sizeof random_buffer;
208 /** @brief Pick a random integer uniformly from [0, limit) */
209 static unsigned long long pick_weight(unsigned long long limit) {
210 unsigned char buf[(sizeof(unsigned long long) * CHAR_BIT + 7)/8], m;
211 unsigned long long t, r, slop;
214 //info("pick_weight: limit = %llu", limit);
216 /* First, decide how many bits of output we actually need; do bytes first
217 * (they're quicker) and then bits.
219 * To speed this up, we could use a binary search if we knew where to
220 * start. (Note that shifting by ULLONG_BITS or more (if such a constant
221 * existed) is undefined behaviour, so we mustn't do that.) Figuring out a
222 * start point involves preprocessor and/or autoconf magic.
224 for (nby = 1, t = (limit - 1) >> 8; t; nby++, t >>= 8)
226 nbi = (nby - 1) << 3; t = limit >> nbi;
227 if (t >> 4) { t >>= 4; nbi += 4; }
228 if (t >> 2) { t >>= 2; nbi += 2; }
229 if (t >> 1) { t >>= 1; nbi += 1; }
231 //info("nby = %d; nbi = %d", nby, nbi);
233 /* Main randomness collection loop. We read a number of bytes from the
234 * randomness source, and glue them together into an integer (dropping
235 * bits off the top byte as necessary). Call the result r; we have
236 * 2^{nbi - 1) <= limit < 2^nbi and r < 2^nbi. If r < limit then we win;
237 * otherwise we try again. Given the above bounds, we expect fewer than 2
240 * Unfortunately there are subtleties. In particular, 2^nbi may in fact be
241 * zero due to overflow. So in fact what we do is compute slop = 2^nbi -
242 * limit > 0; if r < slop then we try again, otherwise r - slop is our
245 slop = (2 << (nbi - 1)) - limit;
246 m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff;
247 //info("slop = %llu", slop);
248 //info("m = 0x%02x", m);
251 /* Actually get some random data. */
252 random_bytes(buf, nby);
254 /* Clobber the top byte. */
257 /* Turn it into an integer. */
258 for (r = 0, i = 0; i < nby; i++)
259 r = (r << 8) | buf[i];
260 //info("r = %llu", r);
266 /** @brief Called for each track */
267 static int collect_tracks_callback(const char *track,
270 void attribute((unused)) *u,
271 DB_TXN attribute((unused)) *tid) {
272 unsigned long weight = compute_weight(track, data, prefs);
274 /* Decide whether this is the winning track.
276 * Suppose that we have n things, and thing i, for 0 <= i < n, has weight
277 * w_i. Let c_i = w_0 + ... + w_{i-1} be the cumulative weight of the
278 * things previous to thing i, and let W = c_n = w_0 + ... + w_{i-1} be the
279 * total weight. We can clearly choose a random thing with the correct
280 * weightings by picking a random number r in [0, W) and chooeing thing i
281 * where c_i <= r < c_i + w_i. But this involves having an enormous list
282 * and taking two passes over it (which has bad locality and is ugly).
284 * Here's another way. Initialize v = -1. Examine the things in order;
285 * for thing i, choose a random number r_i in [0, c_i + w_i). If r_i < w_i
288 * Claim. For all 0 <= i < n, the above algorithm chooses thing i with
291 * Proof. Induction on n. The claim is clear for n = 1. Suppose it's
292 * true for n - 1. Let L be the event that we choose thing n - 1. Clearly
293 * Pr[L] = w_{n-1}/W. Condition on not-L: then the probabilty that we
294 * choose thing i, for 0 <= i < n - 1, is w_i/c_{n-1} (induction
295 * hypothesis); undoing the conditioning gives the desired result.
298 total_weight += weight;
299 if (pick_weight(total_weight) < weight)
306 int main(int argc, char **argv) {
307 int n, logsyslog = !isatty(2), err;
312 if(!setlocale(LC_CTYPE, "")) fatal(errno, "error calling setlocale");
313 while((n = getopt_long(argc, argv, "hVc:dDSs", options, 0)) >= 0) {
316 case 'V': version("disorder-choose");
317 case 'c': configfile = optarg; break;
318 case 'd': debugging = 1; break;
319 case 'D': debugging = 0; break;
320 case 'S': logsyslog = 0; break;
321 case 's': logsyslog = 1; break;
322 default: fatal(0, "invalid option");
326 openlog(progname, LOG_PID, LOG_DAEMON);
327 log_default = &log_syslog;
329 if(config_read(0)) fatal(0, "cannot read configuration");
330 /* Find out current queue/recent list */
333 /* Generate the candidate track list */
334 trackdb_init(TRACKDB_NO_RECOVER);
335 trackdb_open(TRACKDB_NO_UPGRADE|TRACKDB_READ_ONLY);
336 global_tid = trackdb_begin_transaction();
337 if((err = trackdb_get_global_tid("required-tags", global_tid, &tags)))
338 fatal(0, "error getting required-tags: %s", db_strerror(err));
339 required_tags = parsetags(tags);
340 if((err = trackdb_get_global_tid("prohibited-tags", global_tid, &tags)))
341 fatal(0, "error getting prohibited-tags: %s", db_strerror(err));
342 prohibited_tags = parsetags(tags);
343 if(trackdb_scan(0, collect_tracks_callback, 0, global_tid))
345 trackdb_commit_transaction(global_tid);
348 //info("ntracks=%ld total_weight=%lld", ntracks, total_weight);
350 fatal(0, "no tracks match random choice criteria");
352 fatal(0, "internal: failed to pick a track");
354 xprintf("%s", winning);