Put flushing-to-DB in a thread

- flush() and backup_flush() are now async

electrumx/server/block_processor.py

@@ -56,7 +56,7 @@ class Prefetcher(object):
                 if not await self._prefetch_blocks():
                     await asyncio.sleep(5)
             except DaemonError as e:
-                self.logger.info('ignoring daemon error: {}'.format(e))
+                self.logger.info(f'ignoring daemon error: {e}')
 
     def get_prefetched_blocks(self):
         '''Called by block processor when it is processing queued blocks.'''
@@ -183,10 +183,26 @@ class BlockProcessor(electrumx.server.db.DB):
         # is consistent with self.height
         self.state_lock = asyncio.Lock()
 
-    async def run_in_thread_shielded(self, func, *args):
+    async def run_in_thread_with_lock(self, func, *args):
+        # Run in a thread to prevent blocking.  Shielded so that
+        # cancellations from shutdown don't lose work - when the task
+        # completes the data will be flushed and then we shut down.
+        # Take the state lock to be certain in-memory state is
+        # consistent and not being updated elsewhere.
         async with self.state_lock:
             return await asyncio.shield(run_in_thread(func, *args))
 
+    async def _maybe_flush(self):
+        # If caught up, flush everything as client queries are
+        # performed on the DB.
+        if self._caught_up_event.is_set():
+            await self.flush(True)
+        elif time.time() > self.next_cache_check:
+            flush_arg = self.check_cache_size()
+            if flush_arg is not None:
+                await self.flush(flush_arg)
+            self.next_cache_check = time.time() + 30
+
     async def check_and_advance_blocks(self, raw_blocks):
         '''Process the list of raw blocks passed.  Detects and handles
         reorgs.
@@ -201,7 +217,14 @@ class BlockProcessor(electrumx.server.db.DB):
         chain = [self.tip] + [self.coin.header_hash(h) for h in headers[:-1]]
 
         if hprevs == chain:
-            await self.run_in_thread_shielded(self.advance_blocks, blocks)
+            start = time.time()
+            await self.run_in_thread_with_lock(self.advance_blocks, blocks)
+            await self._maybe_flush()
+            if not self.first_sync:
+                s = '' if len(blocks) == 1 else 's'
+                self.logger.info('processed {:,d} block{} in {:.1f}s'
+                                 .format(len(blocks), s,
+                                         time.time() - start))
             if self._caught_up_event.is_set():
                 await self.notifications.on_block(self.touched, self.height)
             self.touched = set()
@@ -226,7 +249,7 @@ class BlockProcessor(electrumx.server.db.DB):
             self.logger.info('chain reorg detected')
         else:
             self.logger.info(f'faking a reorg of {count:,d} blocks')
-        await run_in_thread(self.flush, True)
+        await self.flush(True)
 
         async def get_raw_blocks(last_height, hex_hashes):
             heights = range(last_height, last_height - len(hex_hashes), -1)
@@ -242,7 +265,8 @@ class BlockProcessor(electrumx.server.db.DB):
         hashes = [hash_to_hex_str(hash) for hash in reversed(hashes)]
         for hex_hashes in chunks(hashes, 50):
             raw_blocks = await get_raw_blocks(last, hex_hashes)
-            await self.run_in_thread_shielded(self.backup_blocks, raw_blocks)
+            await self.run_in_thread_with_lock(self.backup_blocks, raw_blocks)
+            await self.backup_flush()
             last -= len(raw_blocks)
         # Truncate header_mc: header count is 1 more than the height.
         self.header_mc.truncate(self.height + 1)
@@ -312,14 +336,16 @@ class BlockProcessor(electrumx.server.db.DB):
         assert not self.db_deletes
         self.history.assert_flushed()
 
-    def flush(self, flush_utxos=False):
+    async def flush(self, flush_utxos):
-        '''Flush out cached state.
-
-        History is always flushed.  UTXOs are flushed if flush_utxos.'''
         if self.height == self.db_height:
             self.assert_flushed()
-            return
+        else:
+            await self.run_in_thread_with_lock(self._flush_body, flush_utxos)
 
+    def _flush_body(self, flush_utxos):
+        '''Flush out cached state.
+
+        History is always flushed.  UTXOs are flushed if flush_utxos.'''
         flush_start = time.time()
         last_flush = self.last_flush
         tx_diff = self.tx_count - self.last_flush_tx_count
@@ -387,23 +413,25 @@ class BlockProcessor(electrumx.server.db.DB):
         self.tx_hashes = []
         self.headers = []
 
-    def backup_flush(self):
+    async def backup_flush(self):
+        assert self.height < self.db_height
+        assert not self.headers
+        assert not self.tx_hashes
+        self.history.assert_flushed()
+        await self.run_in_thread_with_lock(self._backup_flush_body)
+
+    def _backup_flush_body(self):
         '''Like flush() but when backing up.  All UTXOs are flushed.
 
         hashXs - sequence of hashXs which were touched by backing
         up.  Searched for history entries to remove after the backup
         height.
         '''
-        assert self.height < self.db_height
-        self.history.assert_flushed()
-
         flush_start = time.time()
 
         # Backup FS (just move the pointers back)
         self.fs_height = self.height
         self.fs_tx_count = self.tx_count
-        assert not self.headers
-        assert not self.tx_hashes
 
         # Backup history.  self.touched can include other addresses
         # which is harmless, but remove None.
@@ -445,14 +473,14 @@ class BlockProcessor(electrumx.server.db.DB):
         # Flush history if it takes up over 20% of cache memory.
         # Flush UTXOs once they take up 80% of cache memory.
         if utxo_MB + hist_MB >= self.cache_MB or hist_MB >= self.cache_MB // 5:
-            self.flush(utxo_MB >= self.cache_MB * 4 // 5)
+            return utxo_MB >= self.cache_MB * 4 // 5
+        return None
 
     def advance_blocks(self, blocks):
         '''Synchronously advance the blocks.
 
         It is already verified they correctly connect onto our tip.
         '''
-        start = time.time()
         min_height = self.min_undo_height(self.daemon.cached_height())
         height = self.height
 
@@ -468,21 +496,6 @@ class BlockProcessor(electrumx.server.db.DB):
         self.headers.extend(headers)
         self.tip = self.coin.header_hash(headers[-1])
 
-        # If caught up, flush everything as client queries are
-        # performed on the DB.
-        if self._caught_up_event.is_set():
-            self.flush(True)
-        else:
-            if time.time() > self.next_cache_check:
-                self.check_cache_size()
-                self.next_cache_check = time.time() + 30
-
-        if not self.first_sync:
-            s = '' if len(blocks) == 1 else 's'
-            self.logger.info('processed {:,d} block{} in {:.1f}s'
-                             .format(len(blocks), s,
-                                     time.time() - start))
-
     def advance_txs(self, txs):
         self.tx_hashes.append(b''.join(tx_hash for tx, tx_hash in txs))
 
@@ -555,7 +568,6 @@ class BlockProcessor(electrumx.server.db.DB):
             self.tx_counts.pop()
 
         self.logger.info('backed up to height {:,d}'.format(self.height))
-        self.backup_flush()
 
     def backup_txs(self, txs):
         # Prevout values, in order down the block (coinbase first if present)
@@ -756,7 +768,7 @@ class BlockProcessor(electrumx.server.db.DB):
         # Flush everything but with first_sync->False state.
         first_sync = self.first_sync
         self.first_sync = False
-        self.flush(True)
+        await self.flush(True)
         if first_sync:
             self.logger.info(f'{electrumx.version} synced to '
                              f'height {self.height:,d}')
@@ -808,10 +820,9 @@ class BlockProcessor(electrumx.server.db.DB):
                 await group.spawn(self.prefetcher.main_loop(self.height))
                 await group.spawn(self._process_prefetched_blocks())
         finally:
-            async with self.state_lock:
             # Shut down block processing
             self.logger.info('flushing to DB for a clean shutdown...')
-                self.flush(True)
+            await self.flush(True)
 
     def force_chain_reorg(self, count):
         '''Force a reorg of the given number of blocks.