Fix potential race conditions in p2p testing framework

Previously, each NodeConnCB had its own lock to synchronize data structures
used by the testing thread and the networking thread, and NodeConn provided a
separate additional lock for synchronizing access to each send buffer.  This
commit replaces those locks with a single global lock (mininode_lock) that we
use to synchronize access to all data structures shared by the two threads.

Updates comptool and maxblocksinflight to use the new synchronization
semantics, eliminating previous race conditions within comptool, and re-enables
invalidblockrequest.py in travis.

qa/rpc-tests/mininode.py

@@ -26,7 +26,7 @@ import sys
 import random
 import cStringIO
 import hashlib
-from threading import Lock
+from threading import RLock
 from threading import Thread
 import logging
 import copy
@@ -42,6 +42,14 @@ MAX_INV_SZ = 50000
 # using select)
 mininode_socket_map = dict()
 
+# One lock for synchronizing all data access between the networking thread (see
+# NetworkThread below) and the thread running the test logic.  For simplicity,
+# NodeConn acquires this lock whenever delivering a message to to a NodeConnCB,
+# and whenever adding anything to the send buffer (in send_message()).  This
+# lock should be acquired in the thread running the test logic to synchronize
+# access to any data shared with the NodeConnCB or NodeConn.
+mininode_lock = RLock()
+
 # Serialization/deserialization tools
 def sha256(s):
     return hashlib.new('sha256', s).digest()
@@ -980,10 +988,6 @@ class msg_reject(object):
 # Reimplement the on_* functions to provide handling for events
 class NodeConnCB(object):
     def __init__(self):
-        # Acquire on all callbacks -- overkill for now since asyncore is
-        # single-threaded, but may be useful for synchronizing access to
-        # member variables in derived classes.
-        self.cbLock = Lock()
         self.verack_received = False
 
     # Derived classes should call this function once to set the message map
@@ -1009,7 +1013,7 @@ class NodeConnCB(object):
         }
 
     def deliver(self, conn, message):
-        with self.cbLock:
+        with mininode_lock:
             try:
                 self.cbmap[message.command](conn, message)
             except:
@@ -1094,7 +1098,6 @@ class NodeConn(asyncore.dispatcher):
         self.state = "connecting"
         self.network = net
         self.cb = callback
-        self.sendbufLock = Lock()  # for protecting the sendbuffer
         self.disconnect = False
 
         # stuff version msg into sendbuf
@@ -1145,20 +1148,18 @@ class NodeConn(asyncore.dispatcher):
         return True
 
     def writable(self):
-        self.sendbufLock.acquire()
-        length = len(self.sendbuf)
-        self.sendbufLock.release()
+        with mininode_lock:
+            length = len(self.sendbuf)
         return (length > 0)
 
     def handle_write(self):
-        self.sendbufLock.acquire()
-        try:
-            sent = self.send(self.sendbuf)
-        except:
-            self.handle_close()
-            return
-        self.sendbuf = self.sendbuf[sent:]
-        self.sendbufLock.release()
+        with mininode_lock:
+            try:
+                sent = self.send(self.sendbuf)
+            except:
+                self.handle_close()
+                return
+            self.sendbuf = self.sendbuf[sent:]
 
     def got_data(self):
         while True:
@@ -1202,7 +1203,6 @@ class NodeConn(asyncore.dispatcher):
     def send_message(self, message, pushbuf=False):
         if self.state != "connected" and not pushbuf:
             return
-        self.sendbufLock.acquire()
         self.show_debug_msg("Send %s" % repr(message))
         command = message.command
         data = message.serialize()
@@ -1215,9 +1215,9 @@ class NodeConn(asyncore.dispatcher):
             h = sha256(th)
             tmsg += h[:4]
         tmsg += data
-        self.sendbuf += tmsg
-        self.last_sent = time.time()
-        self.sendbufLock.release()
+        with mininode_lock:
+            self.sendbuf += tmsg
+            self.last_sent = time.time()
 
     def got_message(self, message):
         if message.command == "version":