Shard searching for new tracks across multiple tasks

This also has the effect of breaking up the enormous 'updateIndexes'
method into one call per file, which means database updates also no
longer monopolise a single background task for their entire duration.

avg. time per new file is now <140ms for a completely fresh database,
which is pretty good i think!

1 files changed, 29 insertions, 1 deletions

diff --git a/src/tangara/database/database.hpp b/src/tangara/database/database.hpp
index 6994d0b8..6daffd23 100644
--- a/src/tangara/database/database.hpp
+++ b/src/tangara/database/database.hpp
@@ -23,6 +23,8 @@
 #include "database/records.hpp"
 #include "database/tag_parser.hpp"
 #include "database/track.hpp"
+#include "database/track_finder.hpp"
+#include "ff.h"
 #include "leveldb/cache.h"
 #include "leveldb/db.h"
 #include "leveldb/iterator.h"
@@ -93,22 +95,48 @@ class Database {
   leveldb::DB* db_;
   leveldb::Cache* cache_;
 
+  TrackFinder track_finder_;
+
   // Not owned.
   ITagParser& tag_parser_;
   locale::ICollator& collator_;
 
+  /* Internal utility for tracking a currently in-progress index update. */
+  class UpdateTracker {
+   public:
+    UpdateTracker();
+    ~UpdateTracker();
+
+    auto onTrackVerified() -> void;
+    auto onVerificationFinished() -> void;
+    auto onTrackAdded() -> void;
+
+   private:
+    uint32_t num_old_tracks_;
+    uint32_t num_new_tracks_;
+    uint64_t start_time_;
+    uint64_t verification_finish_time_;
+  };
+
   std::atomic<bool> is_updating_;
+  std::unique_ptr<UpdateTracker> update_tracker_;
+
   std::atomic<TrackId> next_track_id_;
 
   Database(leveldb::DB* db,
            leveldb::Cache* cache,
+           tasks::WorkerPool& pool,
            ITagParser& tag_parser,
            locale::ICollator& collator);
 
+  auto processCandidateCallback(FILINFO&, std::string_view) -> void;
+  auto indexingCompleteCallback() -> void;
+
   auto dbCalculateNextTrackId() -> void;
   auto dbMintNewTrackId() -> TrackId;
 
-  auto dbGetTrackData(TrackId id) -> std::shared_ptr<TrackData>;
+  auto dbGetTrackData(leveldb::ReadOptions, TrackId id)
+      -> std::shared_ptr<TrackData>;
 
   auto dbCreateIndexesForTrack(const Track&, leveldb::WriteBatch&) -> void;
   auto dbCreateIndexesForTrack(const TrackData&,