/* * This file is part of DisOrder * Copyright (C) 2008 Richard Kettlewell * Copyright (C) 2008 Mark Wooding * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see . */ /** @file server/choose.c * @brief Random track chooser * * Picks a track at random and writes it to standard output. If for * any reason no track can be picked - even a trivial reason like a * deadlock - it just exits and expects the server to try again. */ #include "disorder-server.h" #define BASE_WEIGHT 90000 static DB_TXN *global_tid; static const struct option options[] = { { "help", no_argument, 0, 'h' }, { "version", no_argument, 0, 'V' }, { "config", required_argument, 0, 'c' }, { "debug", no_argument, 0, 'd' }, { "no-debug", no_argument, 0, 'D' }, { "syslog", no_argument, 0, 's' }, { "no-syslog", no_argument, 0, 'S' }, { 0, 0, 0, 0 } }; /* display usage message and terminate */ static void help(void) { xprintf("Usage:\n" " disorder-choose [OPTIONS]\n" "Options:\n" " --help, -h Display usage message\n" " --version, -V Display version number\n" " --config PATH, -c PATH Set configuration file\n" " --debug, -d Turn on debugging\n" " --[no-]syslog Enable/disable logging to syslog\n" "\n" "Track chooser for DisOrder. Not intended to be run\n" "directly.\n"); xfclose(stdout); exit(0); } /** @brief Sum of all weights */ static unsigned long long total_weight; /** @brief The winning track */ static const char *winning = 0; /** @brief Count of tracks */ static long ntracks; static char **required_tags; static char **prohibited_tags; static int queue_contains(const struct queue_entry *head, const char *track) { const struct queue_entry *q; for(q = head->next; q != head; q = q->next) if(!strcmp(q->track, track)) return 1; return 0; } /** @brief Compute the weight of a track * @param track Track name (UTF-8) * @param data Track data * @param prefs Track preferences * @return Track weight (non-negative) * * Tracks to be excluded entirely are given a weight of 0. */ static unsigned long compute_weight(const char *track, struct kvp *data, struct kvp *prefs) { const char *s; char **track_tags; time_t last, now = time(0); /* Reject tracks not in any collection (race between edit config and * rescan) */ if(!find_track_root(track)) { info("found track not in any collection: %s", track); return 0; } /* Reject aliases to avoid giving aliased tracks extra weight */ if(kvp_get(data, "_alias_for")) return 0; /* Reject tracks with random play disabled */ if((s = kvp_get(prefs, "pick_at_random")) && !strcmp(s, "0")) return 0; /* Reject tracks played within the last 8 hours */ if((s = kvp_get(prefs, "played_time"))) { last = atoll(s); if(now < last + config->replay_min) return 0; } /* Reject tracks currently in the queue or in the recent list */ if(queue_contains(&qhead, track) || queue_contains(&phead, track)) return 0; /* We'll need tags for a number of things */ track_tags = parsetags(kvp_get(prefs, "tags")); /* Reject tracks with prohibited tags */ if(prohibited_tags && tag_intersection(track_tags, prohibited_tags)) return 0; /* Reject tracks that lack required tags */ if(*required_tags && !tag_intersection(track_tags, required_tags)) return 0; /* Use the configured weight if available */ if((s = kvp_get(prefs, "weight"))) { long n; errno = 0; n = strtol(s, 0, 10); if((errno == 0 || errno == ERANGE) && n >= 0) return n; } /* Bias up tracks that were recently added */ if((s = kvp_get(data, "_noticed"))) { const time_t noticed = atoll(s); if(noticed + config->new_bias_age < now) /* Currently we just step up the weight of tracks that are in range. A * more sophisticated approach would be to linearly decay from new_bias * down to BASE_WEIGHT over the course of the new_bias_age interval * starting when the track is added. */ return config->new_bias; } return BASE_WEIGHT; } /** @brief Pick a random integer uniformly from [0, limit) */ static unsigned long long pick_weight(unsigned long long limit) { unsigned char buf[(sizeof(unsigned long long) * CHAR_BIT + 7)/8], m; unsigned long long t, r, slop; int i, nby, nbi; D(("pick_weight: limit = %#016llx", limit)); /* First, decide how many bits of output we actually need; do bytes first * (they're quicker) and then bits. * * To speed this up, we could use a binary search if we knew where to * start. (Note that shifting by ULLONG_BITS or more (if such a constant * existed) is undefined behaviour, so we mustn't do that.) Figuring out a * start point involves preprocessor and/or autoconf magic. */ for (nby = 1, t = (limit - 1) >> 8; t; nby++, t >>= 8) ; nbi = (nby - 1) << 3; t = limit >> nbi; if (t >> 4) { t >>= 4; nbi += 4; } if (t >> 2) { t >>= 2; nbi += 2; } if (t >> 1) { t >>= 1; nbi += 1; } nbi++; D(("nby = %d; nbi = %d", nby, nbi)); /* Main randomness collection loop. We read a number of bytes from the * randomness source, and glue them together into an integer (dropping * bits off the top byte as necessary). Call the result r; we have * 2^{nbi - 1) <= limit < 2^nbi and r < 2^nbi. If r < limit then we win; * otherwise we try again. Given the above bounds, we expect fewer than 2 * iterations. * * Unfortunately there are subtleties. In particular, 2^nbi may in fact be * zero due to overflow. So in fact what we do is compute slop = 2^nbi - * limit > 0; if r < slop then we try again, otherwise r - slop is our * winner. */ slop = ((unsigned long long)2 << (nbi - 1)) - limit; m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff; D(("slop = %#016llx", slop)); D(("m = 0x%02x", m)); do { /* Actually get some random data. */ random_get(buf, nby); /* Clobber the top byte. */ buf[0] &= m; /* Turn it into an integer. */ for (r = 0, i = 0; i < nby; i++) r = (r << 8) | buf[i]; D(("r = %#016llx", r)); } while (r < slop); D((" result=%#016llx", r - slop)); return r - slop; } /** @brief Called for each track */ static int collect_tracks_callback(const char *track, struct kvp *data, struct kvp *prefs, void attribute((unused)) *u, DB_TXN attribute((unused)) *tid) { unsigned long weight = compute_weight(track, data, prefs); /* Decide whether this is the winning track. * * Suppose that we have n things, and thing i, for 0 <= i < n, has weight * w_i. Let c_i = w_0 + ... + w_{i-1} be the cumulative weight of the * things previous to thing i, and let W = c_n = w_0 + ... + w_{i-1} be the * total weight. We can clearly choose a random thing with the correct * weightings by picking a random number r in [0, W) and chooeing thing i * where c_i <= r < c_i + w_i. But this involves having an enormous list * and taking two passes over it (which has bad locality and is ugly). * * Here's another way. Initialize v = -1. Examine the things in order; * for thing i, choose a random number r_i in [0, c_i + w_i). If r_i < w_i * then set v <- i. * * Claim. For all 0 <= i < n, the above algorithm chooses thing i with * probability w_i/W. * * Proof. Induction on n. The claim is clear for n = 1. Suppose it's * true for n - 1. Let L be the event that we choose thing n - 1. Clearly * Pr[L] = w_{n-1}/W. Condition on not-L: then the probabilty that we * choose thing i, for 0 <= i < n - 1, is w_i/c_{n-1} (induction * hypothesis); undoing the conditioning gives the desired result. */ D(("consider %s", track)); if(weight) { total_weight += weight; if (pick_weight(total_weight) < weight) winning = track; } ntracks++; return 0; } int main(int argc, char **argv) { int n, logsyslog = !isatty(2), err; const char *tags; set_progname(argv); mem_init(); if(!setlocale(LC_CTYPE, "")) fatal(errno, "error calling setlocale"); while((n = getopt_long(argc, argv, "hVc:dDSs", options, 0)) >= 0) { switch(n) { case 'h': help(); case 'V': version("disorder-choose"); case 'c': configfile = optarg; break; case 'd': debugging = 1; break; case 'D': debugging = 0; break; case 'S': logsyslog = 0; break; case 's': logsyslog = 1; break; default: fatal(0, "invalid option"); } } if(logsyslog) { openlog(progname, LOG_PID, LOG_DAEMON); log_default = &log_syslog; } if(config_read(0)) fatal(0, "cannot read configuration"); /* Find out current queue/recent list */ queue_read(); recent_read(); /* Generate the candidate track list */ trackdb_init(TRACKDB_NO_RECOVER); trackdb_open(TRACKDB_NO_UPGRADE|TRACKDB_READ_ONLY); global_tid = trackdb_begin_transaction(); if((err = trackdb_get_global_tid("required-tags", global_tid, &tags))) fatal(0, "error getting required-tags: %s", db_strerror(err)); required_tags = parsetags(tags); if((err = trackdb_get_global_tid("prohibited-tags", global_tid, &tags))) fatal(0, "error getting prohibited-tags: %s", db_strerror(err)); prohibited_tags = parsetags(tags); if(trackdb_scan(0, collect_tracks_callback, 0, global_tid)) { global_tid->abort(global_tid); exit(1); } trackdb_commit_transaction(global_tid); trackdb_close(); trackdb_deinit(); D(("ntracks=%ld total_weight=%lld", ntracks, total_weight)); if(!total_weight) fatal(0, "no tracks match random choice criteria"); if(!winning) fatal(0, "internal: failed to pick a track"); /* Pick a track */ xprintf("%s", winning); xfclose(stdout); return 0; } /* Local Variables: c-basic-offset:2 comment-column:40 fill-column:79 indent-tabs-mode:nil End: */