Update various comments

electrumx/server/mempool.py

@@ -22,6 +22,7 @@ from electrumx.server.db import UTXO
 @attr.s(slots=True)
 class MemPoolTx(object):
     prevouts = attr.ib()
+    # A pair is a (hashX, value) tuple
     in_pairs = attr.ib()
     out_pairs = attr.ib()
     fee = attr.ib()
@@ -32,14 +33,11 @@ class MemPool(object):
     '''Representation of the daemon's mempool.
 
     Updated regularly in caught-up state.  Goal is to enable efficient
-    response to the value() and transactions() calls.
+    response to the calls in the external interface.  To that end we
+    maintain the following maps:
 
-    To that end we maintain the following maps:
-
-       tx_hash -> MemPoolTx
-       hashX   -> set of all tx hashes in which the hashX appears
-
-    A pair is a (hashX, value) tuple.  tx hashes are binary not strings.
+       tx:     tx_hash -> MemPoolTx
+       hashXs: hashX   -> set of all hashes of txs touching the hashX
     '''
 
     def __init__(self, coin, tasks, daemon, notifications, lookup_utxos):
@@ -117,28 +115,25 @@ class MemPool(object):
             # Spend the prevouts
             unspent.difference_update(tx.prevouts)
 
-            # Save the in_pairs, compute the fee,  and accept the TX
+            # Save the in_pairs, compute the fee and accept the TX
             tx.in_pairs = tuple(in_pairs)
             tx.fee = (sum(v for hashX, v in tx.in_pairs) -
                       sum(v for hashX, v in tx.out_pairs))
             txs[hash] = tx
+
             for hashX, value in itertools.chain(tx.in_pairs, tx.out_pairs):
                 touched.add(hashX)
                 hashXs[hashX].add(hash)
 
         return deferred, {prevout: utxo_map[prevout] for prevout in unspent}
 
-    async def _refresh_hashes(self, single_pass):
-        '''Return a (hash set, height) pair when we're sure which height they
-        are for.'''
-        refresh_event = asyncio.Event()
-        loop = self.tasks.loop
+    async def _refresh_hashes(self, once):
+        '''Refresh our view of the daemon's mempool.'''
         for loop_count in itertools.count():
             height = self.daemon.cached_height()
             hex_hashes = await self.daemon.mempool_hashes()
             if height != await self.daemon.height():
                 continue
-            loop.call_later(5, refresh_event.set)
             hashes = set(hex_str_to_hash(hh) for hh in hex_hashes)
             touched = await self._process_mempool(hashes)
             await self.notifications.on_mempool(touched, height)
@@ -146,10 +141,9 @@ class MemPool(object):
             # can be expensive.
             if loop_count % 100 == 0:
                 await self.tasks.run_in_thread(self._update_histogram)
-            if single_pass:
+            if once:
                 return
-            await refresh_event.wait()
-            refresh_event.clear()
+            await asyncio.sleep(5)
 
     async def _process_mempool(self, all_hashes):
         # Re-sync with the new set of hashes
@@ -201,8 +195,7 @@ class MemPool(object):
         hex_hashes_iter = (hash_to_hex_str(hash) for hash in hashes)
         raw_txs = await self.daemon.getrawtransactions(hex_hashes_iter)
 
-        def deserialize_txs():
-            # This function is pure
+        def deserialize_txs():    # This function is pure
             to_hashX = self.coin.hashX_from_script
             deserializer = self.coin.DESERIALIZER
 
@@ -213,15 +206,11 @@ class MemPool(object):
                 if not raw_tx:
                     continue
                 tx, tx_size = deserializer(raw_tx).read_tx_and_vsize()
-
-                # Convert the tx outputs into (hashX, value) pairs
-                txout_pairs = tuple((to_hashX(txout.pk_script), txout.value)
-                                    for txout in tx.outputs)
-
-                # Convert the tx inputs to (prev_hash, prev_idx) pairs
+                # Convert the inputs and outputs into (hashX, value) pairs
                 txin_pairs = tuple((txin.prev_hash, txin.prev_idx)
                                    for txin in tx.inputs)
-
+                txout_pairs = tuple((to_hashX(txout.pk_script), txout.value)
+                                    for txout in tx.outputs)
                 txs[hash] = MemPoolTx(txin_pairs, None, txout_pairs,
                                       0, tx_size)
             return txs
@@ -231,7 +220,8 @@ class MemPool(object):
 
         # Determine all prevouts not in the mempool, and fetch the
         # UTXO information from the database.  Failed prevout lookups
-        # return None - concurrent database updates happen
+        # return None - concurrent database updates happen - which is
+        # relied upon by _accept_transactions
         prevouts = tuple(prevout for tx in tx_map.values()
                          for prevout in tx.prevouts
                          if prevout[0] not in all_hashes)
@@ -240,7 +230,10 @@ class MemPool(object):
 
         return self._accept_transactions(tx_map, utxo_map, touched)
 
+    #
     # External interface
+    #
+
     async def start_and_wait_for_sync(self):
         '''Starts the mempool synchronizer.
 
@@ -249,11 +242,11 @@ class MemPool(object):
         self.logger.info('beginning processing of daemon mempool.  '
                          'This can take some time...')
         start = time.time()
-        await self._refresh_hashes(True)
+        await self._refresh_hashes(once=True)
         elapsed = time.time() - start
         self.logger.info(f'synced in {elapsed:.2f}s')
         self.tasks.create_task(self._log_stats())
-        self.tasks.create_task(self._refresh_hashes(False))
+        self.tasks.create_task(self._refresh_hashes(once=False))
 
     async def balance_delta(self, hashX):
         '''Return the unconfirmed amount in the mempool for hashX.