trim the recording playback cache a bit

It had an Arc which in hindsight isn't necessary; the actual video index
generation is fast anyway. This saves a couple pointers per cache entry and
the overhead of chasing them. LruCache itself also has some extra pointers on
it but that's something to address another day.

src/db.rs

@@ -200,6 +200,21 @@ impl rusqlite::types::FromSql for FromSqlUuid {
     }
 }
 
+/// A box with space for the uuid (initially uninitialized) and the video index.
+/// The caller must fill the uuid bytes.
+struct PlaybackData(Box<[u8]>);
+
+impl rusqlite::types::FromSql for PlaybackData {
+    fn column_result(value: rusqlite::types::ValueRef) -> rusqlite::types::FromSqlResult<Self> {
+        let blob = value.as_blob()?;
+        let len = 16 + blob.len();
+        let mut v = Vec::with_capacity(len);
+        unsafe { v.set_len(len) };
+        v[16..].copy_from_slice(blob);
+        Ok(PlaybackData(v.into_boxed_slice()))
+    }
+}
+
 /// A concrete box derived from a ISO/IEC 14496-12 section 8.5.2 VisualSampleEntry box. Describes
 /// the codec, width, height, etc.
 #[derive(Debug)]
@@ -243,11 +258,20 @@ pub struct ListAggregatedRecordingsRow {
     pub run_start_id: i32,
 }
 
-/// Select fields from the `recordings_playback` table. Retrieve with `get_recording_playback`.
+/// Select fields from the `recordings_playback` table. Retrieve with `with_recording_playback`.
 #[derive(Debug)]
-pub struct RecordingPlayback {
+pub struct RecordingPlayback<'a> {
     pub sample_file_uuid: Uuid,
-    pub video_index: Box<[u8]>,
+    pub video_index: &'a [u8],
+}
+
+impl<'a> RecordingPlayback<'a> {
+    fn new(data: &'a [u8]) -> Self {
+        RecordingPlayback {
+            sample_file_uuid: Uuid::from_bytes(&data[..16]).unwrap(),
+            video_index: &data[16..],
+        }
+    }
 }
 
 /// Bitmask in the `flags` field in the `recordings` table; see `schema.sql`.
@@ -497,7 +521,7 @@ struct State {
     cameras_by_uuid: BTreeMap<Uuid, i32>,
     video_sample_entries: BTreeMap<i32, Arc<VideoSampleEntry>>,
     list_recordings_by_time_sql: String,
-    playback_cache: RefCell<LruCache<i64, Arc<RecordingPlayback>, fnv::FnvBuildHasher>>,
+    playback_cache: RefCell<LruCache<i64, Box<[u8]>, fnv::FnvBuildHasher>>,
 }
 
 /// A high-level transaction. This manages the SQLite transaction and the matching modification to
@@ -949,15 +973,17 @@ impl LockedDatabase {
         Ok(())
     }
 
-    /// Gets a single `recording_playback` row.
+    /// Calls `f` with a single `recording_playback` row.
+    /// Note the lock is held for the duration of `f`.
     /// This uses a LRU cache to reduce the number of retrievals from the database.
-    pub fn get_recording_playback(&self, camera_id: i32, recording_id: i32)
-        -> Result<Arc<RecordingPlayback>, Error> {
+    pub fn with_recording_playback<F, R>(&self, camera_id: i32, recording_id: i32, f: F)
+                                      -> Result<R, Error>
+    where F: FnOnce(&RecordingPlayback) -> Result<R, Error> {
         let composite_id = composite_id(camera_id, recording_id);
         let mut cache = self.state.playback_cache.borrow_mut();
         if let Some(r) = cache.get_mut(&composite_id) {
             trace!("cache hit for recording {}/{}", camera_id, recording_id);
-            return Ok(r.clone());
+            return f(&RecordingPlayback::new(r));
         }
         trace!("cache miss for recording {}/{}", camera_id, recording_id);
         let mut stmt = self.conn.prepare_cached(GET_RECORDING_PLAYBACK_SQL)?;
@@ -965,12 +991,14 @@ impl LockedDatabase {
         if let Some(row) = rows.next() {
             let row = row?;
             let uuid: FromSqlUuid = row.get_checked(0)?;
-            let r = Arc::new(RecordingPlayback {
-                sample_file_uuid: uuid.0,
-                video_index: row.get_checked::<_, Vec<u8>>(1)?.into_boxed_slice(),
-            });
-            cache.insert(composite_id, r.clone());
-            return Ok(r);
+            let data = {
+                let mut data: PlaybackData = row.get_checked(1)?;
+                data.0[0..16].copy_from_slice(uuid.0.as_bytes());
+                data.0
+            };
+            let result = f(&RecordingPlayback::new(&data));
+            cache.insert(composite_id, data);
+            return result;
         }
         Err(Error::new(format!("no such recording {}/{}", camera_id, recording_id)))
     }
@@ -1467,7 +1495,7 @@ mod tests {
         assert_eq!(1, rows);
 
         // TODO: list_aggregated_recordings.
-        // TODO: get_recording_playback.
+        // TODO: with_recording_playback.
     }
 
     fn assert_unsorted_eq<T>(mut a: Vec<T>, mut b: Vec<T>)

src/mp4.rs

@@ -352,11 +352,10 @@ impl Segment {
                       -> Result<(), Error>
     where F: FnOnce(&[u8], SegmentLengths) -> &[u8] {
         let index = self.index.borrow_with(|| {
-            self.build_index(db)
-                .map_err(|e| {
-                    error!("Unable to build index for segment: {:?}", e);
-                    ()
-                })
+            db.lock()
+              .with_recording_playback(self.s.camera_id, self.s.recording_id,
+                                       |playback| self.build_index(playback))
+              .map_err(|e| { error!("Unable to build index for segment: {:?}", e); })
         });
         let index = match *index {
             Ok(ref b) => &b[..],
@@ -380,7 +379,7 @@ impl Segment {
     fn stsz(buf: &[u8], lens: SegmentLengths) -> &[u8] { &buf[lens.stts .. lens.stts + lens.stsz] }
     fn stss(buf: &[u8], lens: SegmentLengths) -> &[u8] { &buf[lens.stts + lens.stsz ..] }
 
-    fn build_index(&self, db: &db::Database) -> Result<Box<[u8]>, Error> {
+    fn build_index(&self, playback: &db::RecordingPlayback) -> Result<Box<[u8]>, Error> {
         let s = &self.s;
         let lens = self.lens();
         let len = lens.stts + lens.stsz + lens.stss;
@@ -395,7 +394,7 @@ impl Segment {
             let mut frame = 0;
             let mut key_frame = 0;
             let mut last_start_and_dur = None;
-            s.foreach(db, |it| {
+            s.foreach(playback, |it| {
                 last_start_and_dur = Some((it.start_90k, it.duration_90k));
                 BigEndian::write_u32(&mut stts[8*frame .. 8*frame+4], 1);
                 BigEndian::write_u32(&mut stts[8*frame+4 .. 8*frame+8], it.duration_90k as u32);
@@ -1152,8 +1151,11 @@ impl File {
     fn write_video_sample_data(&self, i: usize, r: Range<u64>, out: &mut io::Write)
                                -> Result<(), Error> {
         let s = &self.segments[i];
-        let rec = self.db.lock().get_recording_playback(s.s.camera_id, s.s.recording_id)?;
-        let f = self.dir.open_sample_file(rec.sample_file_uuid)?;
+        let uuid = {
+            self.db.lock().with_recording_playback(s.s.camera_id, s.s.recording_id,
+                                                   |p| Ok(p.sample_file_uuid))?
+        };
+        let f = self.dir.open_sample_file(uuid)?;
         mmapfile::MmapFileSlice::new(f, s.s.sample_file_range()).write_to(r, out)
     }
 
@@ -1786,8 +1788,8 @@ mod bench {
         let db = TestDb::new();
         testutil::add_dummy_recordings_to_db(&db.db, 1);
 
-        let segment = {
         let db = db.db.lock();
+        let segment = {
             let all_time = recording::Time(i64::min_value()) .. recording::Time(i64::max_value());
             let mut row = None;
             db.list_recordings_by_time(testutil::TEST_CAMERA_ID, all_time, |r| {
@@ -1798,9 +1800,12 @@ mod bench {
             let rel_range_90k = 0 .. row.duration_90k;
             super::Segment::new(&db, &row, rel_range_90k, 1).unwrap()
         };
-        let v = segment.build_index(&db.db).unwrap();  // warm.
+        db.with_recording_playback(segment.s.camera_id, segment.s.recording_id, |playback| {
+            let v = segment.build_index(playback).unwrap();  // warm.
             b.bytes = v.len() as u64;  // define the benchmark performance in terms of output bytes.
-        b.iter(|| segment.build_index(&db.db).unwrap());
+            b.iter(|| segment.build_index(playback).unwrap());
+            Ok(())
+        }).unwrap();
     }
 
     /// Benchmarks serving the generated part of a `.mp4` file (up to the first byte from disk).

src/recording.rs

@@ -406,7 +406,7 @@ impl Segment {
         }
 
         // Slow path. Need to iterate through the index.
-        let playback = db.get_recording_playback(self_.camera_id, self_.recording_id)?;
+        db.with_recording_playback(self_.camera_id, self_.recording_id, |playback| {
             let data = &(&playback).video_index;
             let mut it = SampleIndexIterator::new();
             if !it.next(data)? {
@@ -451,6 +451,7 @@ impl Segment {
                 recording.video_sample_entry.id |
                 (((it.duration_90k == 0) as i32) << 31);
             Ok(self_)
+        })
     }
 
     pub fn video_sample_entry_id(&self) -> i32 {
@@ -467,11 +468,10 @@ impl Segment {
 
     /// Iterates through each frame in the segment.
     /// Must be called without the database lock held; retrieves video index from the cache.
-    pub fn foreach<F>(&self, db: &db::Database, mut f: F) -> Result<(), Error>
+    pub fn foreach<F>(&self, playback: &db::RecordingPlayback, mut f: F) -> Result<(), Error>
     where F: FnMut(&SampleIndexIterator) -> Result<(), Error> {
         trace!("foreach on recording {}/{}: {} frames, actual_time_90k: {:?}",
               self.camera_id, self.recording_id, self.frames, self.actual_time_90k());
-        let playback = db.lock().get_recording_playback(self.camera_id, self.recording_id)?;
         let data = &(&playback).video_index;
         let mut it = self.begin;
         if it.uninitialized() {
@@ -634,6 +634,15 @@ mod tests {
         }
     }
 
+    fn get_frames<F, T>(db: &db::Database, segment: &Segment, f: F) -> Vec<T>
+    where F: Fn(&SampleIndexIterator) -> T {
+        let mut v = Vec::new();
+        db.lock().with_recording_playback(segment.camera_id, segment.recording_id, |playback| {
+            segment.foreach(playback, |it| { v.push(f(it)); Ok(()) })
+        }).unwrap();
+        v
+    }
+
     /// Tests that a `Segment` correctly can clip at the beginning and end.
     /// This is a simpler case; all sync samples means we can start on any frame.
     #[test]
@@ -649,9 +658,7 @@ mod tests {
         // Time range [2, 2 + 4 + 6 + 8) means the 2nd, 3rd, 4th samples should be
         // included.
         let segment = Segment::new(&db.db.lock(), &row, 2 .. 2+4+6+8).unwrap();
-        let mut v = Vec::new();
-        segment.foreach(&db.db, |it| { v.push(it.duration_90k); Ok(()) }).unwrap();
-        assert_eq!(&v, &[4, 6, 8]);
+        assert_eq!(&get_frames(&db.db, &segment, |it| it.duration_90k), &[4, 6, 8]);
     }
 
     /// Half sync frames means starting from the last sync frame <= desired point.
@@ -668,9 +675,7 @@ mod tests {
         // Time range [2 + 4 + 6, 2 + 4 + 6 + 8) means the 4th sample should be included.
         // The 3rd also gets pulled in because it is a sync frame and the 4th is not.
         let segment = Segment::new(&db.db.lock(), &row, 2+4+6 .. 2+4+6+8).unwrap();
-        let mut v = Vec::new();
-        segment.foreach(&db.db, |it| { v.push(it.duration_90k); Ok(()) }).unwrap();
-        assert_eq!(&v, &[6, 8]);
+        assert_eq!(&get_frames(&db.db, &segment, |it| it.duration_90k), &[6, 8]);
     }
 
     #[test]
@@ -682,9 +687,7 @@ mod tests {
         let db = TestDb::new();
         let row = db.create_recording_from_encoder(encoder);
         let segment = Segment::new(&db.db.lock(), &row, 1 .. 2).unwrap();
-        let mut v = Vec::new();
-        segment.foreach(&db.db, |it| { v.push(it.bytes); Ok(()) }).unwrap();
-        assert_eq!(&v, &[2, 3]);
+        assert_eq!(&get_frames(&db.db, &segment, |it| it.bytes), &[2, 3]);
     }
 
     /// Test a `Segment` which uses the whole recording.
@@ -700,9 +703,7 @@ mod tests {
         let db = TestDb::new();
         let row = db.create_recording_from_encoder(encoder);
         let segment = Segment::new(&db.db.lock(), &row, 0 .. 2+4+6+8+10).unwrap();
-        let mut v = Vec::new();
-        segment.foreach(&db.db, |it| { v.push(it.duration_90k); Ok(()) }).unwrap();
-        assert_eq!(&v, &[2, 4, 6, 8, 10]);
+        assert_eq!(&get_frames(&db.db, &segment, |it| it.duration_90k), &[2, 4, 6, 8, 10]);
     }
 
     #[test]
@@ -714,9 +715,7 @@ mod tests {
         let db = TestDb::new();
         let row = db.create_recording_from_encoder(encoder);
         let segment = Segment::new(&db.db.lock(), &row, 0 .. 2).unwrap();
-        let mut v = Vec::new();
-        segment.foreach(&db.db, |it| { v.push(it.bytes); Ok(()) }).unwrap();
-        assert_eq!(&v, &[1, 2, 3]);
+        assert_eq!(&get_frames(&db.db, &segment, |it| it.bytes), &[1, 2, 3]);
     }
 
     // TODO: test segment error cases involving mismatch between row frames/key_frames and index.

src/streamer.rs

@@ -306,7 +306,7 @@ mod tests {
     }
 
     fn get_frames(db: &db::LockedDatabase, camera_id: i32, recording_id: i32) -> Vec<Frame> {
-        let rec = db.get_recording_playback(camera_id, recording_id).unwrap();
+        db.with_recording_playback(camera_id, recording_id, |rec| {
             let mut it = recording::SampleIndexIterator::new();
             let mut frames = Vec::new();
             while it.next(&rec.video_index).unwrap() {
@@ -316,7 +316,8 @@ mod tests {
                     is_key: it.is_key(),
                 });
             }
-        frames
+            Ok(frames)
+        }).unwrap()
     }
 
     #[test]