X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~mdw/git/disorder/blobdiff_plain/af7a85b709c60a644fe04e77a3289bcd120ba1b2..16fb2830d52c1420afdee555a566d72a065d9616:/server/play.c

diff --git a/server/play.c b/server/play.c
index f38c9d5..5503263 100644
--- a/server/play.c
+++ b/server/play.c
@@ -1,78 +1,53 @@
 /*
  * This file is part of DisOrder.
- * Copyright (C) 2004, 2005, 2006, 2007 Richard Kettlewell
+ * Copyright (C) 2004-2009 Richard Kettlewell
  *
- * This program is free software; you can redistribute it and/or modify
+ * 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 2 of the License, or
+ * 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.
- *
+ * 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, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
- * USA
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/** @file server/play.c
+ * @brief Playing tracks
  */
 
-#include <config.h>
-#include "types.h"
-
-#include <sys/types.h>
-#include <sys/time.h>
-#include <unistd.h>
-#include <errno.h>
-#include <fnmatch.h>
-#include <time.h>
-#include <signal.h>
-#include <stdlib.h>
-#include <assert.h>
-#include <sys/socket.h>
-#include <string.h>
-#include <stdio.h>
-#include <pcre.h>
+#include "disorder-server.h"
 #include <ao/ao.h>
-#include <sys/wait.h>
-#include <sys/un.h>
-
-#include "event.h"
-#include "log.h"
-#include "mem.h"
-#include "configuration.h"
-#include "queue.h"
-#include "server-queue.h"
-#include "rights.h"
-#include "trackdb.h"
-#include "play.h"
-#include "plugin.h"
-#include "wstat.h"
-#include "eventlog.h"
-#include "logfd.h"
-#include "syscalls.h"
-#include "speaker-protocol.h"
-#include "disorder.h"
-#include "signame.h"
-#include "hash.h"
 
 #define SPEAKER "disorder-speaker"
 
+/** @brief The current playing track or NULL */
 struct queue_entry *playing;
+
+/** @brief Set when paused */
 int paused;
 
 static void finished(ev_source *ev);
 
+/** @brief File descriptor of our end of the socket to the speaker */
 static int speaker_fd = -1;
+
+/** @brief Mapping of track IDs to associated decoder process IDs */
 static hash *player_pids;
+
+/** @brief Set when shutting down */
 static int shutting_down;
 
+/** @brief Remember a player's PID */
 static void store_player_pid(const char *id, pid_t pid) {
   if(!player_pids) player_pids = hash_new(sizeof (pid_t));
   hash_add(player_pids, id, &pid, HASH_INSERT_OR_REPLACE);
 }
 
+/** @brief Find a player's PID */
 static pid_t find_player_pid(const char *id) {
   pid_t *pidp;
 
@@ -80,11 +55,20 @@ static pid_t find_player_pid(const char *id) {
   return -1;
 }
 
+/** @brief Discard a player's ID->PID mappin
+ *
+ * Used when the player terminates.
+ */
 static void forget_player_pid(const char *id) {
   if(player_pids) hash_remove(player_pids, id);
 }
 
-/* called when speaker process terminates */
+/** @brief Called when speaker process terminates
+ *
+ * Currently kills of DisOrder completely.  A future version could terminate
+ * the speaker when nothing was going on, or recover from failures, though any
+ * tracks with decoders already started would need to have them restarted.
+ */
 static int speaker_terminated(ev_source attribute((unused)) *ev,
 			      pid_t attribute((unused)) pid,
 			      int attribute((unused)) status,
@@ -94,7 +78,7 @@ static int speaker_terminated(ev_source attribute((unused)) *ev,
 	wstat(status));
 }
 
-/* called when speaker process has something to say */
+/** @brief Called when we get a message from the speaker process */
 static int speaker_readable(ev_source *ev, int fd,
 			    void attribute((unused)) *u) {
   struct speaker_message sm;
@@ -123,11 +107,12 @@ static int speaker_readable(ev_source *ev, int fd,
     playing->sofar = sm.data;
     break;
   default:
-    error(0, "unknown message type %d", sm.type);
+    error(0, "unknown speaker message type %d", sm.type);
   }
   return 0;
 }
 
+/** @brief Initialize the speaker process */
 void speaker_setup(ev_source *ev) {
   int sp[2];
   pid_t pid;
@@ -163,9 +148,11 @@ void speaker_setup(ev_source *ev) {
   /* Wait for the speaker to be ready */
   speaker_recv(speaker_fd, &sm);
   nonblock(speaker_fd);
-  ev_fd(ev, ev_read, speaker_fd, speaker_readable, 0, "speaker read");
+  if(ev_fd(ev, ev_read, speaker_fd, speaker_readable, 0, "speaker read") < 0)
+    fatal(0, "error registering speaker socket fd");
 }
 
+/** @brief Tell the speaker to reload its configuration */
 void speaker_reload(void) {
   struct speaker_message sm;
 
@@ -174,28 +161,21 @@ void speaker_reload(void) {
   speaker_send(speaker_fd, &sm);
 }
 
-/* timeout for play retry */
-static int play_again(ev_source *ev,
-		      const struct timeval attribute((unused)) *now,
-		      void attribute((unused)) *u) {
-  D(("play_again"));
-  play(ev);
-  return 0;
-}
-
-/* try calling play() again after @offset@ seconds */
-static void retry_play(ev_source *ev, int offset) {
-  struct timeval w;
-
-  D(("retry_play(%d)", offset));
-  gettimeofday(&w, 0);
-  w.tv_sec += offset;
-  ev_timeout(ev, 0, &w, play_again, 0);
-}
-
-/* Called when the currently playing track finishes playing.  This
- * might be because the player finished or because the speaker process
- * told us so. */
+/** @brief Called when the currently playing track finishes playing
+ * @param ev Event loop or NULL
+ *
+ * There are three places this is called from:
+ * 
+ * 1) speaker_readable(), when the speaker tells us the playing track finished.
+ * (Technically the speaker lies a little to arrange for gapless play.)
+ *
+ * 2) player_finished(), when the player for a non-raw track (i.e. one that
+ * does not use the speaker) finishes.
+ *
+ * 3) quitting(), after signalling the decoder or player but possible before it
+ * has actually terminated.  In this case @p ev is NULL, inhibiting any further
+ * attempt to play anything.
+ */
 static void finished(ev_source *ev) {
   D(("finished playing=%p", (void *)playing));
   if(!playing)
@@ -219,10 +199,20 @@ static void finished(ev_source *ev) {
   recent_write();
   forget_player_pid(playing->id);
   playing = 0;
-  if(ev) retry_play(ev, config->gap);
+  /* Try to play something else */
+  /* TODO re-support config->gap? */
+  if(ev)
+    play(ev);
 }
 
-/* Called when a player terminates. */
+/** @brief Called when a player or decoder process terminates
+ *
+ * This is called when a decoder process terminates (which might actually be
+ * some time before the speaker reports it as finished) or when a non-raw
+ * (i.e. non-speaker) player terminates.  In the latter case it's imaginable
+ * that the OS has buffered the last few samples.
+ * 
+ */
 static int player_finished(ev_source *ev,
 			   pid_t pid,
 			   int status,
@@ -241,12 +231,15 @@ static int player_finished(ev_source *ev,
   case playing_unplayed:
   case playing_random:
     /* If this was a pre-prepared track then either it failed or we
-     * deliberately stopped it because it was removed from the queue or moved
-     * down it.  So leave it state alone for future use. */
+     * deliberately stopped it: it might have been removed from the queue, or
+     * moved down the queue, or the speaker might be on a break.  So we leave
+     * it state alone for future use.
+     */
     break;
   default:
     /* We actually started playing this track. */
     if(status) {
+      /* Don't override 'scratched' with 'failed'. */
       if(q->state != playing_scratched)
 	q->state = playing_failed;
     } else 
@@ -269,7 +262,7 @@ static int player_finished(ev_source *ev,
   return 0;
 }
 
-/* Find the player for Q */
+/** @brief Find the player for @p q */
 static int find_player(const struct queue_entry *q) {
   int n;
   
@@ -283,15 +276,23 @@ static int find_player(const struct queue_entry *q) {
 }
 
 /* Return values from start() */
-#define START_OK 0			/**< @brief Succeeded. */
-#define START_HARDFAIL 1		/**< @brief Track is broken. */
-#define START_SOFTFAIL 2	   /**< @brief Track OK, system (temporarily?) broken */
+#define START_OK 0	   /**< @brief Succeeded. */
+#define START_HARDFAIL 1   /**< @brief Track is broken. */
+#define START_SOFTFAIL 2   /**< @brief Track OK, system (temporarily?) broken */
 
 /** @brief Play or prepare @p q
  * @param ev Event loop
  * @param q Track to play/prepare
  * @param prepare_only If true, only prepares track
  * @return @ref START_OK, @ref START_HARDFAIL or @ref START_SOFTFAIL
+ *
+ * TODO: probably ought to be split up into separate prepare() and start()
+ * operations, the latter calling the former if necessary and perhaps the two
+ * sharing some subprocess creation logic.
+ *
+ * "Preparing" a track means starting a background decoder and connecting it to
+ * the speaker process.  Obviously this only applies to raw-format
+ * (i.e. speaker-using) players.
  */
 static int start(ev_source *ev,
 		 struct queue_entry *q,
@@ -315,7 +316,7 @@ static int start(ev_source *ev,
   memset(&sm, 0, sizeof sm);
   D(("start %s %d", q->id, prepare_only));
   if(q->prepared) {
-    /* The track is alraedy prepared */
+    /* The track is already prepared */
     if(!prepare_only) {
       /* We want to run it, since it's prepared the answer is to tell the
        * speaker to set it off */
@@ -335,20 +336,24 @@ static int start(ev_source *ev,
   if(prepare_only
      && (q->type & DISORDER_PLAYER_TYPEMASK) != DISORDER_PLAYER_RAW)
     return START_OK;
-  /* Call the prefork function. */
+  /* Call the prefork function in the player module.  None of the built-in
+   * modules use this so it's not well tested, unfortunately. */
   p = trackdb_rawpath(q->track);
   if(q->type & DISORDER_PLAYER_PREFORK)
     if(!(q->data = play_prefork(q->pl, p))) {
       error(0, "prefork function for %s failed", q->track);
       return START_HARDFAIL;
     }
-  /* Use the second arg as the tag if available (it's probably a command name),
+  /* Capture the player/decoder's stderr and feed it into our logs.
+   *
+   * Use the second arg as the tag if available (it's probably a command name),
    * otherwise the module name. */
   if(!isatty(2))
     lfd = logfd(ev, (config->player.s[n].s[2]
 		     ? config->player.s[n].s[2] : config->player.s[n].s[1]));
   else
     lfd = -1;
+  /* Parse player arguments */
   optc = config->player.s[n].n - 2;
   optv = (void *)&config->player.s[n].s[2];
   while(optc > 0 && optv[0][0] == '-') {
@@ -370,17 +375,21 @@ static int start(ev_source *ev,
       return START_HARDFAIL;
     }
   }
+  /* Create the subprocess */
   switch(pid = fork()) {
-  case 0:			/* child */
+  case 0:
+    /* Child of disorderd */
     exitfn = _exit;
     progname = "disorderd-fork";
     ev_signal_atfork(ev);
     signal(SIGPIPE, SIG_DFL);
+    /* Send our log output to DisOrder's logs */
     if(lfd != -1) {
       xdup2(lfd, 1);
       xdup2(lfd, 2);
       xclose(lfd);			/* tidy up */
     }
+    /* Create a new process group, ID = child PID */
     setpgid(0, 0);
     if((q->type & DISORDER_PLAYER_TYPEMASK) == DISORDER_PLAYER_RAW) {
       /* "Raw" format players always have their output send down a pipe
@@ -400,9 +409,12 @@ static int start(ev_source *ev,
       xshutdown(np[0], SHUT_WR);	/* normalize reads from np[0] */
       blocking(np[0]);
       blocking(np[1]);
-      /* Start disorder-normalize */
+      /* Start disorder-normalize.  We double-fork so that nothing has to wait
+       * for disorder-normalize. */
       if(!(npid = xfork())) {
+        /* Grandchild of disorderd */
 	if(!xfork()) {
+          /* Great-grandchild of disorderd */
 	  /* Connect to the speaker process */
 	  memset(&addr, 0, sizeof addr);
 	  addr.sun_family = AF_UNIX;
@@ -411,12 +423,14 @@ static int start(ev_source *ev,
 	  sfd = xsocket(PF_UNIX, SOCK_STREAM, 0);
 	  if(connect(sfd, (const struct sockaddr *)&addr, sizeof addr) < 0)
 	    fatal(errno, "connecting to %s", addr.sun_path);
+          /* Send the ID, with a NATIVE-ENDIAN 32 bit length */
 	  l = strlen(q->id);
 	  if(write(sfd, &l, sizeof l) < 0
 	     || write(sfd, q->id, l) < 0)
 	    fatal(errno, "writing to %s", addr.sun_path);
 	  /* Await the ack */
-	  read(sfd, &l, 1);
+	  if (read(sfd, &l, 1) < 0) 
+		fatal(errno, "reading ack from %s", addr.sun_path);
 	  /* Plumbing */
 	  xdup2(np[0], 0);
 	  xdup2(sfd, 1);
@@ -424,7 +438,19 @@ static int start(ev_source *ev,
 	  xclose(np[1]);
 	  xclose(sfd);
 	  /* Ask the speaker to actually start playing the track; we do it here
-	   * so it's definitely after ack. */
+	   * so it's definitely after ack.
+           *
+           * This is actually insufficient.  If the track is prepared and then
+           * very shortly afterwards played, then the race we're trying to
+           * avoid here will still exist.  So either the speaker must cope with
+           * SM_PLAY before connection has arrived (in which case we might as
+           * well move the SM_PLAY somewhere saner) or we must do more work
+           * here to avoid the race.
+           *
+           * In fact the current speaker can indeed cope with SM_PLAY before
+           * the connection arrives.  So this code can probably be moved
+           * somewhere saner in due course.  TODO!
+           */
 	  if(!prepare_only) {
 	    strcpy(sm.id, q->id);
 	    sm.type = SM_PLAY;
@@ -438,12 +464,14 @@ static int start(ev_source *ev,
 		 "--config", configfile,
 		 (char *)0);
 	  fatal(errno, "executing disorder-normalize");
-	  /* end of the innermost fork */
+	  /* End of the great-grandchild of disorderd */
 	}
+        /* Back in the grandchild of disorderd */
 	_exit(0);
-	/* end of the middle fork */
+        /* End of the grandchild of disorderd */
       }
-      /* Wait for the middle fork to finish */
+      /* Back in the child of disorderd */
+      /* Wait for the grandchild of disordered to finish */
       while(waitpid(npid, &n, 0) < 0 && errno == EINTR)
 	;
       /* Pass the file descriptor to the driver in an environment
@@ -454,6 +482,8 @@ static int start(ev_source *ev,
       /* Close all the FDs we don't need */
       xclose(np[0]);
     }
+    /* Wait for a device to clear.  This ugliness is now deprecated and will
+     * eventually be removed. */
     if(waitdevice) {
       ao_initialize();
       if(*waitdevice) {
@@ -480,8 +510,10 @@ static int start(ev_source *ev,
 	       optv, optc,
 	       p,
 	       q->track);
+    /* End of child of disorderd */
     _exit(0);
-  case -1:			/* error */
+  case -1:
+    /* Back in disorderd (child could not be created) */
     error(errno, "error calling fork");
     if(q->type & DISORDER_PLAYER_PREFORK)
       play_cleanup(q->pl, q->data);	/* else would leak */
@@ -489,16 +521,33 @@ static int start(ev_source *ev,
       xclose(lfd);
     return START_SOFTFAIL;
   }
+  /* Back in disorderd (child was created) */
+  /* Remmber the PID */
   store_player_pid(q->id, pid);
+  /* This track is prepared.  (Non-raw tracks are by implication prepared as
+   * soon as they are playing, but really the question doesn't make much sense
+   * for them.) */
   q->prepared = 1;
   if(lfd != -1)
     xclose(lfd);
+  /* Set the child's process group ID.
+   *
+   * But wait, didn't we already set it in the child?  Yes, but it's possible
+   * that we'll need to address it by process group ID before it gets that far,
+   * so we set it here too.  One or the other may fail but as long as one
+   * succeeds that's fine.
+   */
   setpgid(pid, pid);
+  /* Ask the event loop to tell us when the child terminates */
   ev_child(ev, pid, 0, player_finished, q);
   D(("player subprocess ID %lu", (unsigned long)pid));
   return START_OK;
 }
 
+/** @brief Prepare a track for later play
+ *
+ * Only applies to raw-format (speaker-using) players.
+ */
 int prepare(ev_source *ev,
 	    struct queue_entry *q) {
   int n;
@@ -513,6 +562,12 @@ int prepare(ev_source *ev,
   return start(ev, q, 1/*prepare_only*/); /* Prepare it */
 }
 
+/** @brief Abandon a queue entry
+ *
+ * Called from c_remove() (but NOT when scratching a track).  Only does
+ * anything to raw-format tracks.  Terminates the background decoder and tells
+ * the speaker process to cancel the track.
+ */
 void abandon(ev_source attribute((unused)) *ev,
 	     struct queue_entry *q) {
   struct speaker_message sm;
@@ -531,58 +586,74 @@ void abandon(ev_source attribute((unused)) *ev,
   speaker_send(speaker_fd, &sm);
 }
 
-int add_random_track(void) {
+/** @brief Called with a new random track
+ * @param ev Event loop
+ * @param track Track name
+ */
+static void chosen_random_track(ev_source *ev,
+				const char *track) {
+  struct queue_entry *q;
+
+  if(!track)
+    return;
+  /* Add the track to the queue */
+  q = queue_add(track, 0, WHERE_END, origin_random);
+  D(("picked %p (%s) at random", (void *)q, q->track));
+  queue_write();
+  /* Maybe a track can now be played */
+  play(ev);
+}
+
+/** @brief Maybe add a randomly chosen track
+ * @param ev Event loop
+ *
+ * Picking can take some time so the track will only be added after this
+ * function has returned.
+ */
+void add_random_track(ev_source *ev) {
   struct queue_entry *q;
-  const char *p;
   long qlen = 0;
-  int rc = 0;
 
   /* If random play is not enabled then do nothing. */
   if(shutting_down || !random_is_enabled())
-    return 0;
+    return;
   /* Count how big the queue is */
   for(q = qhead.next; q != &qhead; q = q->next)
     ++qlen;
-  /* Add random tracks until the queue is at the right size */
-  while(qlen < config->queue_pad) {
-    /* Try to pick a random track */
-    if(!(p = trackdb_random(16))) {
-      rc = -1;
-      break;
-    }
-    /* Add it to the end of the queue. */
-    q = queue_add(p, 0, WHERE_END);
-    q->state = playing_random;
-    D(("picked %p (%s) at random", (void *)q, q->track));
-    ++qlen;
-  }
-  /* Commit the queue */
-  queue_write();
-  return rc;
+  /* If it's smaller than the desired size then add a track */
+  if(qlen < config->queue_pad)
+    trackdb_request_random(ev, chosen_random_track);
 }
 
-/* try to play a track */
+/** @brief Attempt to play something
+ *
+ * This is called from numerous locations - whenever it might conceivably have
+ * become possible to play something.
+ */
 void play(ev_source *ev) {
   struct queue_entry *q;
   int random_enabled = random_is_enabled();
 
   D(("play playing=%p", (void *)playing));
+  /* If we're shutting down, or there's something playing, or playing is not
+   * enabled, give up now */
   if(shutting_down || playing || !playing_is_enabled()) return;
-  /* If the queue is empty then add a random track. */
+  /* See if there's anything to play */
   if(qhead.next == &qhead) {
-    if(!random_enabled)
-      return;
-    if(add_random_track()) {
-      /* On error, try again in 10s. */
-      retry_play(ev, 10);
-      return;
-    }
-    /* Now there must be at least one track in the queue. */
+    /* Queue is empty.  We could just wait around since there are periodic
+     * attempts to add a random track anyway.  However they are rarer than
+     * attempts to force a track so we initiate one now. */
+    add_random_track(ev);
+    /* chosen_random_track() will call play() when a new random track has been
+     * added to the queue. */
+    return;
   }
+  /* There must be at least one track in the queue. */
   q = qhead.next;
-  /* If random play is disabled but the track is a random one then don't play
-   * it.  play() will be called again when random play is re-enabled. */
-  if(!random_enabled && q->state == playing_random)
+  /* If random play is disabled but the track is a non-adopted random one
+   * then don't play it.  play() will be called again when random play is
+   * re-enabled. */
+  if(!random_enabled && q->origin == origin_random)
     return;
   D(("taken %p (%s) from queue", (void *)q, q->track));
   /* Try to start playing. */
@@ -593,25 +664,19 @@ void play(ev_source *ev) {
       queue_played(q);
       recent_write();
     }
-    if(qhead.next == &qhead)
-      /* Queue is empty, wait a bit before trying something else (so we don't
-       * sit there looping madly in the presence of persistent problem).  Note
-       * that we might not reliably get a random track lookahead in this case,
-       * but if we get here then really there are bigger problems. */
-      retry_play(ev, 1);
-    else
-      /* More in queue, try again now. */
-      play(ev);
+    /* Oh well, try the next one */
+    play(ev);
     break;
   case START_SOFTFAIL:
-    /* Try same track again in a bit. */
-    retry_play(ev, 10);
+    /* We'll try the same track again shortly. */
     break;
   case START_OK:
+    /* Remove from the queue */
     if(q == qhead.next) {
       queue_remove(q, 0);
       queue_write();
     }
+    /* It's become the playing track */
     playing = q;
     time(&playing->played);
     playing->state = playing_started;
@@ -620,7 +685,7 @@ void play(ev_source *ev) {
 	     playing->submitter ? playing->submitter : (const char *)0,
 	     (const char *)0);
     /* Maybe add a random track. */
-    add_random_track();
+    add_random_track(ev);
     /* If there is another track in the queue prepare it now.  This could
      * potentially be a just-added random track. */
     if(qhead.next != &qhead)
@@ -629,39 +694,49 @@ void play(ev_source *ev) {
   }
 }
 
+/** @brief Return true if play is enabled */
 int playing_is_enabled(void) {
   const char *s = trackdb_get_global("playing");
 
   return !s || !strcmp(s, "yes");
 }
 
+/** @brief Enable play */
 void enable_playing(const char *who, ev_source *ev) {
   trackdb_set_global("playing", "yes", who);
   /* Add a random track if necessary. */
-  add_random_track();
+  add_random_track(ev);
   play(ev);
 }
 
+/** @brief Disable play */
 void disable_playing(const char *who) {
   trackdb_set_global("playing", "no", who);
 }
 
+/** @brief Return true if random play is enabled */
 int random_is_enabled(void) {
   const char *s = trackdb_get_global("random-play");
 
   return !s || !strcmp(s, "yes");
 }
 
+/** @brief Enable random play */
 void enable_random(const char *who, ev_source *ev) {
   trackdb_set_global("random-play", "yes", who);
-  add_random_track();
+  add_random_track(ev);
   play(ev);
 }
 
+/** @brief Disable random play */
 void disable_random(const char *who) {
   trackdb_set_global("random-play", "no", who);
 }
 
+/** @brief Scratch a track
+ * @param User responsible (or NULL)
+ * @param Track ID (or NULL for current)
+ */
 void scratch(const char *who, const char *id) {
   struct queue_entry *q;
   struct speaker_message sm;
@@ -672,19 +747,27 @@ void scratch(const char *who, const char *id) {
      playing ? playing->state : 0,
      id ? id : "(none)",
      playing ? playing->id : "(none)"));
+  /* There must be a playing track; it must be in a scratchable state; if a
+   * specific ID was mentioned it must be that track. */
   if(playing
      && (playing->state == playing_started
 	 || playing->state == playing_paused)
      && (!id
 	 || !strcmp(id, playing->id))) {
+    /* Update state (for the benefit of the 'recent' list) */
     playing->state = playing_scratched;
     playing->scratched = who ? xstrdup(who) : 0;
+    /* Find the player and kill the whole process group */
     if((pid = find_player_pid(playing->id)) > 0) {
-      D(("kill -%d %lu", config->signal, (unsigned long)pid));
+      D(("kill -%d -%lu", config->signal, (unsigned long)pid));
       kill(-pid, config->signal);
       forget_player_pid(playing->id);
-    } else
+    } else {
+      /* TODO if the background decoder finished and the speaker is working
+       * through buffered data this will produce a bogus log message. */
       error(0, "could not find PID for %s", playing->id);
+    }
+    /* Tell the speaker, if we think it'll care */
     if((playing->type & DISORDER_PLAYER_TYPEMASK) == DISORDER_PLAYER_RAW) {
       memset(&sm, 0, sizeof sm);
       sm.type = SM_CANCEL;
@@ -696,14 +779,14 @@ void scratch(const char *who, const char *id) {
      * bother if playing is disabled) */
     if(playing_is_enabled() && config->scratch.n) {
       int r = rand() * (double)config->scratch.n / (RAND_MAX + 1.0);
-      q = queue_add(config->scratch.s[r], who, WHERE_START);
-      q->state = playing_isscratch;
+      q = queue_add(config->scratch.s[r], who, WHERE_START, origin_scratch);
     }
     notify_scratch(playing->track, playing->submitter, who,
 		   time(0) - playing->played);
   }
 }
 
+/** @brief Called from quit() to tear down eveyrthing belonging to this file */
 void quitting(ev_source *ev) {
   struct queue_entry *q;
   pid_t pid;
@@ -715,8 +798,11 @@ void quitting(ev_source *ev) {
     if((pid = find_player_pid(playing->id)) > 0) {
       kill(-pid, config->signal);
       forget_player_pid(playing->id);
-    } else
+    } else{
+      /* TODO if the background decoder finished and the speaker is working
+       * through buffered data this will produce a bogus log message. */
       error(0, "could not find PID for %s", playing->id);
+    }
     playing->state = playing_quitting;
     finished(0);
   }
@@ -726,13 +812,17 @@ void quitting(ev_source *ev) {
       D(("kill -%d %lu", config->signal, (unsigned long)pid));
       kill(-pid, config->signal);
       forget_player_pid(q->id);
-    } else
+    } else {
+      /* TODO if we never started a background decoder then this will produce a
+       * very bogus log message (see issue 32) */
       error(0, "could not find PID for %s", q->id);
+    }
   /* Don't need the speaker any more */
   ev_fd_cancel(ev, ev_read, speaker_fd);
   xclose(speaker_fd);
 }
 
+/** @brief Pause the playing track */
 int pause_playing(const char *who) {
   struct speaker_message sm;
   long played;
@@ -769,6 +859,7 @@ int pause_playing(const char *who) {
   return 0;
 }
 
+/** @brief Resume playing after a pause */
 void resume_playing(const char *who) {
   struct speaker_message sm;
 
@@ -803,5 +894,6 @@ Local Variables:
 c-basic-offset:2
 comment-column:40
 fill-column:79
+indent-tabs-mode:nil
 End:
 */