/*
* 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
* deadlock - it just exits and expects the server to try again.
*/
-#include <config.h>
-#include "types.h"
-
-#include <getopt.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <db.h>
-#include <locale.h>
-#include <errno.h>
-#include <sys/types.h>
-#include <unistd.h>
-#include <pcre.h>
-#include <string.h>
-#include <fcntl.h>
-#include <syslog.h>
-#include <time.h>
-
-#include "configuration.h"
-#include "log.h"
-#include "defs.h"
-#include "mem.h"
-#include "kvp.h"
-#include "syscalls.h"
-#include "printf.h"
-#include "trackdb.h"
-#include "trackdb-int.h"
-#include "version.h"
-#include "trackname.h"
-#include "queue.h"
-#include "server-queue.h"
+#include "disorder-server.h"
+
+#define BASE_WEIGHT 90000
static DB_TXN *global_tid;
" --debug, -d Turn on debugging\n"
" --[no-]syslog Enable/disable logging to syslog\n"
"\n"
- "Track choose for DisOrder. Not intended to be run\n"
+ "Track chooser for DisOrder. Not intended to be run\n"
"directly.\n");
xfclose(stdout);
exit(0);
}
-
-/** @brief Weighted track record */
-struct weighted_track {
- /** @brief Next track in the list */
- struct weighted_track *next;
- /** @brief Track name */
- const char *track;
- /** @brief Weight for this track (always positive) */
- unsigned long weight;
-};
-
-/** @brief List of tracks with nonzero weight */
-static struct weighted_track *tracks;
-
/** @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;
struct kvp *prefs) {
const char *s;
char **track_tags;
- time_t last, now;
+ time_t last, now = time(0);
/* Reject tracks not in any collection (race between edit config and
* rescan) */
/* Reject tracks played within the last 8 hours */
if((s = kvp_get(prefs, "played_time"))) {
last = atoll(s);
- now = time(0);
if(now < last + config->replay_min)
return 0;
}
if((errno == 0 || errno == ERANGE) && n >= 0)
return n;
}
-
- return 90000;
-}
-/** @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);
+ /* Bias up tracks that were recently added */
+ if((s = kvp_get(data, "_noticed"))) {
+ const time_t noticed = atoll(s);
- if(weight) {
- struct weighted_track *const t = xmalloc(sizeof *t);
-
- /* Clamp weight so that we can fit in billions of tracks when we do
- * arithmetic in long long */
- if(weight > 0x7fffffff)
- weight = 0x7fffffff;
- t->next = tracks;
- t->track = track;
- t->weight = weight;
- tracks = t;
- total_weight += weight;
- ++ntracks;
+ 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 0;
-}
-
-/** @brief Pick a random integer uniformly from [0, limit) */
-static void random_bytes(unsigned char *buf, size_t n) {
- static int fd = -1;
- int r;
-
- if(fd < 0) {
- if((fd = open("/dev/urandom", O_RDONLY)) < 0)
- fatal(errno, "opening /dev/urandom");
- }
- if((r = read(fd, buf, n)) < 0)
- fatal(errno, "reading /dev/urandom");
- if((size_t)r < n)
- fatal(0, "short read from /dev/urandom");
+
+ return BASE_WEIGHT;
}
/** @brief Pick a random integer uniformly from [0, limit) */
unsigned long long t, r, slop;
int i, nby, nbi;
- //info("pick_weight: limit = %llu", limit);
+ 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.
if (t >> 2) { t >>= 2; nbi += 2; }
if (t >> 1) { t >>= 1; nbi += 1; }
nbi++;
- //info("nby = %d; nbi = %d", nby, 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
* limit > 0; if r < slop then we try again, otherwise r - slop is our
* winner.
*/
- slop = (2 << (nbi - 1)) - limit;
+ slop = ((unsigned long long)2 << (nbi - 1)) - limit;
m = nbi & 7 ? (1 << (nbi & 7)) - 1 : 0xff;
- //info("slop = %llu", slop);
- //info("m = 0x%02x", m);
+ D(("slop = %#016llx", slop));
+ D(("m = 0x%02x", m));
do {
/* Actually get some random data. */
- random_bytes(buf, nby);
+ 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];
- //info("r = %llu", r);
+ D(("r = %#016llx", r));
} while (r < slop);
+ D((" result=%#016llx", r - slop));
return r - slop;
}
-/** @brief Pick a track at random and write it to stdout */
-static void pick_track(void) {
- long long w;
- struct weighted_track *t;
+/** @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);
- w = pick_weight(total_weight);
- t = tracks;
- while(t && w >= t->weight) {
- w -= t->weight;
- t = t->next;
+ /* 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;
}
- if(!t)
- fatal(0, "ran out of tracks but %lld weighting left", w);
- xprintf("%s", t->track);
+ ntracks++;
+ return 0;
}
int main(int argc, char **argv) {
trackdb_commit_transaction(global_tid);
trackdb_close();
trackdb_deinit();
- //info("ntracks=%ld total_weight=%lld", ntracks, total_weight);
+ 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 */
- pick_track();
+ xprintf("%s", winning);
xfclose(stdout);
return 0;
}
~mdw / disorder / blobdiff