Dont use a timer for indexing progress

This makes things very slow as it requires locking the database ever
second. Instead use the db's event system to deliver indexing progress
changed events.

src/calibre/db/cache.py

@@ -431,6 +431,7 @@ class Cache:
     def initialize_fts(self):
         self.fts_queue_thread = None
         self.fts_job_queue = Queue()
+        self.fts_indexing_left = self.fts_indexing_total = 0
         fts = self.backend.initialize_fts(weakref.ref(self))
         if self.is_fts_enabled():
             self.start_fts_pool()
@@ -448,14 +449,20 @@ class Cache:
     def is_fts_enabled(self):
         return self.backend.fts_enabled
 
-    @read_api
+    @api
     def fts_indexing_progress(self):
-        if not self.is_fts_enabled():
-            return 0, 0
-        num_to_scan = self.backend.fts.number_dirtied()
-        if not num_to_scan:
-            return 0, 1
-        return num_to_scan, (self.backend.get('SELECT COUNT(*) FROM main.data')[0][0] or 0)
+        return self.fts_indexing_left, self.fts_indexing_total
+
+    def _update_fts_indexing_numbers(self):
+        # this is called when new formats are added and when a format is
+        # indexed, but NOT when books or formats are deleted, so total may not
+        # be up to date.
+        nl = self.backend.fts.number_dirtied()
+        nt = self.backend.get('SELECT COUNT(*) FROM main.data')[0][0] or 0
+        if (self.fts_indexing_left, self.fts_indexing_total) != (nl, nt):
+            self.fts_indexing_left = nl
+            self.fts_indexing_total = nt
+            self.event_dispatcher(EventType.indexing_progress_changed, nl, nt)
 
     @write_api
     def enable_fts(self, enabled=True, start_pool=True):
@@ -527,10 +534,13 @@ class Cache:
         if not self.backend.fts_enabled:
             return
         self.fts_job_queue.put(True)
+        self._update_fts_indexing_numbers()
 
     @write_api
     def commit_fts_result(self, book_id, fmt, fmt_size, fmt_hash, text, err_msg):
-        return self.backend.commit_fts_result(book_id, fmt, fmt_size, fmt_hash, text, err_msg)
+        ans = self.backend.commit_fts_result(book_id, fmt, fmt_size, fmt_hash, text, err_msg)
+        self._update_fts_indexing_numbers()
+        return ans
 
     @api
     def reindex_fts(self):

src/calibre/db/listeners.py

@@ -40,6 +40,9 @@ class EventType(Enum):
     #: When a book format is edited, with arguments: (book_id, fmt)
     book_edited = auto()
 
+    #: When the indexing progress changes
+    indexing_progress_changed = auto()
+
 
 class EventDispatcher(Thread):
 

src/calibre/gui2/fts/scan.py

@@ -5,13 +5,15 @@
 import os
 from qt.core import (
     QCheckBox, QDialog, QDialogButtonBox, QHBoxLayout, QIcon, QLabel, QPushButton,
-    QRadioButton, QTimer, QVBoxLayout, QWidget, pyqtSignal
+    QRadioButton, QVBoxLayout, QWidget, pyqtSignal
 )
 
 from calibre import detect_ncpus
 from calibre.db.cache import Cache
+from calibre.db.listeners import EventType
 from calibre.gui2.dialogs.confirm_delete import confirm
 from calibre.gui2.fts.utils import get_db
+from calibre.gui2.ui import get_gui
 
 
 class IndexingProgress:
@@ -139,11 +141,20 @@ class ScanStatus(QWidget):
         l.addStretch(10)
         self.apply_fts_state()
         self.enable_fts.toggled.connect(self.change_fts_state)
-        self.indexing_status_timer = t = QTimer(self)
-        t.timeout.connect(self.update_stats)
-        t.setInterval(1000)
-        t.start()
         self.update_stats()
+        gui = get_gui()
+        if gui is None:
+            self.db.add_listener(self)
+        else:
+            gui.add_db_listener(self.gui_update_event)
+
+    def gui_update_event(self, db, event_type, event_data):
+        if event_type is EventType.indexing_progress_changed:
+            self.update_stats()
+
+    def __call__(self, event_type, library_id, event_data):
+        if event_type is EventType.indexing_progress_changed:
+            self.update_stats()
 
     def update_stats(self):
         changed = self.indexing_progress.update(*self.db.fts_indexing_progress())
@@ -200,10 +211,9 @@ class ScanStatus(QWidget):
         self.apply_fts_state()
 
     def startup(self):
-        self.indexing_status_timer.start()
+        pass
 
     def shutdown(self):
-        self.indexing_status_timer.stop()
         self.scan_progress.slow_button.setChecked(True)
         self.reset_indexing_state_for_current_db()