diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index d18bffa986..144d19b119 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -2379,27 +2379,31 @@ class Cache:
     def __del__(self):
         self.close()
 
-    @write_api
+    @api
     def close(self):
-        if hasattr(self, 'close_called'):
-            return
-        self.close_called = True
-        self.shutting_down = True
-        self.event_dispatcher.close()
-        if self.fts_queue_thread is not None:
-            self.fts_job_queue.put(None)
-        from calibre.customize.ui import available_library_closed_plugins
-        for plugin in available_library_closed_plugins():
-            try:
-                plugin.run(self)
-            except Exception:
-                import traceback
-                traceback.print_exc()
+        with self.write_lock:
+            if hasattr(self, 'close_called'):
+                return
+            self.close_called = True
+            self.shutting_down = True
+            self.event_dispatcher.close()
+            if self.fts_queue_thread is not None:
+                self.fts_job_queue.put(None)
+            from calibre.customize.ui import available_library_closed_plugins
+            for plugin in available_library_closed_plugins():
+                try:
+                    plugin.run(self)
+                except Exception:
+                    import traceback
+                    traceback.print_exc()
+        # the fts supervisor thread could be in the middle of committing a
+        # result to the db, so holding a lock here will cause a deadlock
         self.backend.shutdown_fts()
         if self.fts_queue_thread is not None:
             self.fts_queue_thread.join()
             self.fts_queue_thread = None
-        self.backend.close()
+        with self.write_lock:
+            self.backend.close()
 
     @property
     def is_closed(self):
diff --git a/src/calibre/db/fts/pool.py b/src/calibre/db/fts/pool.py
index 768d82a2ce..675dd7addd 100644
--- a/src/calibre/db/fts/pool.py
+++ b/src/calibre/db/fts/pool.py
@@ -129,6 +129,7 @@ class Pool:
         self.workers = []
         self.initialized = Event()
         self.dbref = dbref
+        self.keep_going = True
 
     def initialize(self):
         if not self.initialized.is_set():
@@ -202,10 +203,13 @@ class Pool:
 
     def shutdown(self):
         if self.initialized.is_set():
-            self.supervise_queue.put(quit)
+            self.keep_going = False
+            for i in range(2):
+                self.supervise_queue.put(quit)
             for w in self.workers:
                 w.keep_going = False
-                self.jobs_queue.put(quit)
+                for i in range(2*len(self.workers)):
+                    self.jobs_queue.put(quit)
             self.supervisor_thread.join()
             for w in self.workers:
                 w.join()
@@ -219,7 +223,7 @@ class Pool:
             db.queue_next_fts_job()
 
     def supervise(self):
-        while True:
+        while self.keep_going:
             x = self.supervise_queue.get()
             try:
                 if x is check_for_work: