blockchain: blockchains_lock needed to write/iterate global dict

electrum/blockchain.py

@@ -74,6 +74,8 @@ def hash_header(header: dict) -> str:
 
 
 blockchains = {}
+blockchains_lock = threading.Lock()
+
 
 def read_blockchains(config):
     blockchains[0] = Blockchain(config, 0, None)
@@ -118,7 +120,8 @@ class Blockchain(util.PrintError):
         return blockchains[self.parent_id]
 
     def get_max_child(self) -> Optional[int]:
-        children = list(filter(lambda y: y.parent_id==self.forkpoint, blockchains.values()))
+        with blockchains_lock: chains = list(blockchains.values())
+        children = list(filter(lambda y: y.parent_id==self.forkpoint, chains))
         return max([x.forkpoint for x in children]) if children else None
 
     def get_forkpoint(self) -> int:
@@ -237,21 +240,23 @@ class Blockchain(util.PrintError):
         self.write(parent_data, 0)
         parent.write(my_data, (forkpoint - parent.forkpoint)*HEADER_SIZE)
         # store file path
-        for b in blockchains.values():
+        with blockchains_lock: chains = list(blockchains.values())
+        for b in chains:
             b.old_path = b.path()
         # swap parameters
         self.parent_id = parent.parent_id; parent.parent_id = parent_id
         self.forkpoint = parent.forkpoint; parent.forkpoint = forkpoint
         self._size = parent._size; parent._size = parent_branch_size
         # move files
-        for b in blockchains.values():
+        for b in chains:
             if b in [self, parent]: continue
             if b.old_path != b.path():
                 self.print_error("renaming", b.old_path, b.path())
                 os.rename(b.old_path, b.path())
         # update pointers
-        blockchains[self.forkpoint] = self
-        blockchains[parent.forkpoint] = parent
+        with blockchains_lock:
+            blockchains[self.forkpoint] = self
+            blockchains[parent.forkpoint] = parent
 
     def assert_headers_file_available(self, path):
         if os.path.exists(path):
@@ -417,14 +422,16 @@ class Blockchain(util.PrintError):
 def check_header(header: dict) -> Optional[Blockchain]:
     if type(header) is not dict:
         return None
-    for b in blockchains.values():
+    with blockchains_lock: chains = list(blockchains.values())
+    for b in chains:
         if b.check_header(header):
             return b
     return None
 
 
 def can_connect(header: dict) -> Optional[Blockchain]:
-    for b in blockchains.values():
+    with blockchains_lock: chains = list(blockchains.values())
+    for b in chains:
         if b.can_connect(header):
             return b
     return None

electrum/interface.py

@@ -510,8 +510,9 @@ class Interface(PrintError):
                     chain = self.blockchain.check_header(bad_header)
                 if not chain:
                     b = forkfun(bad_header)
-                    assert bad not in blockchain.blockchains, (bad, list(blockchain.blockchains.keys()))
-                    blockchain.blockchains[bad] = b
+                    with blockchain.blockchains_lock:
+                        assert bad not in blockchain.blockchains, (bad, list(blockchain.blockchains))
+                        blockchain.blockchains[bad] = b
                     self.blockchain = b
                     height = b.forkpoint + 1
                     assert b.forkpoint == bad
@@ -540,7 +541,8 @@ class Interface(PrintError):
             return True
 
         bad, bad_header = height, header
-        local_max = max([0] + [x.height() for x in blockchain.blockchains.values()]) if 'mock' not in header else float('inf')
+        with blockchain.blockchains_lock: chains = list(blockchain.blockchains.values())
+        local_max = max([0] + [x.height() for x in chains]) if 'mock' not in header else float('inf')
         height = min(local_max + 1, height - 1)
         while await iterate():
             bad, bad_header = height, header

electrum/network.py

@@ -177,7 +177,7 @@ class Network(PrintError):
             config = {}  # Do not use mutables as default values!
         self.config = SimpleConfig(config) if isinstance(config, dict) else config
         self.num_server = 10 if not self.config.get('oneserver') else 0
-        blockchain.blockchains = blockchain.read_blockchains(self.config)  # note: needs self.blockchains_lock
+        blockchain.blockchains = blockchain.read_blockchains(self.config)
         self.print_error("blockchains", list(blockchain.blockchains.keys()))
         self.blockchain_index = config.get('blockchain_index', 0)
         if self.blockchain_index not in blockchain.blockchains.keys():
@@ -199,7 +199,6 @@ class Network(PrintError):
         self.interface_lock = threading.RLock()            # <- re-entrant
         self.callback_lock = threading.Lock()
         self.recent_servers_lock = threading.RLock()       # <- re-entrant
-        self.blockchains_lock = threading.Lock()
 
         self.server_peers = {}  # returned by interface (servers that the main interface knows about)
         self.recent_servers = self.read_recent_servers()  # note: needs self.recent_servers_lock
@@ -711,8 +710,7 @@ class Network(PrintError):
     @with_interface_lock
     def get_blockchains(self):
         out = {}
-        with self.blockchains_lock:
-            blockchain_items = list(blockchain.blockchains.items())
+        with blockchain.blockchains_lock: blockchain_items = list(blockchain.blockchains.items())
         for k, b in blockchain_items:
             r = list(filter(lambda i: i.blockchain==b, list(self.interfaces.values())))
             if r: