patch time.time in historical_connections to avoid windows failures; fix race...

patch time.time in historical_connections to avoid windows failures; fix race condition in pool.availableGC

* patch time.time in historical_connections to avoid windows failures.

* Also use a mock version of datetime.datetime.utcnow.

We can't patch the method in-place because it's an extension type.

* synchronize sleep with time

* increment by less than the pool timeout to avoid a race condition.

* Avoid mutating the dict as we iter over it.

Seen in Python 3.4 tests:

File "/home/travis/build/zopefoundation/ZODB/src/ZODB/historical_connections.txt", line 263, in historical_connections.txt
Failed example:
    conn = db.open()
Exception raised:
    Traceback (most recent call last):
      File "/opt/python/3.4.2/lib/python3.4/doctest.py", line 1324, in __run
        compileflags, 1), test.globs)
      File "<doctest historical_connections.txt[0]>", line 1, in <module>
        conn = db.open()
      File "/home/travis/build/zopefoundation/ZODB/src/ZODB/DB.py", line 761, in open
        self.historical_pool.availableGC()
      File "/home/travis/build/zopefoundation/ZODB/src/ZODB/DB.py", line 277, in availableGC
        for key, pool in self.pools.items():
    RuntimeError: dictionary changed size during iteration

src/ZODB/DB.py

@@ -274,7 +274,7 @@ class KeyedConnectionPool(AbstractConnectionPool):
             pool.map(f)
 
     def availableGC(self):
-        for key, pool in self.pools.items():
+        for key, pool in list(self.pools.items()):
             pool.availableGC()
             if not pool.all:
                 del self.pools[key]

src/ZODB/historical_connections.txt

@@ -2,6 +2,28 @@
 Historical Connections
 ======================
 
+.. We need to mess with time to prevent spurious test failures on windows
+
+    >>> _now = 1231019584.0
+    >>> def faux_time_time():
+    ...     global _now
+    ...     _now += .001 # must be less than 0.01
+    ...     return _now
+    >>> import time
+    >>> real_time_time = time.time
+    >>> real_time_sleep = time.sleep
+    >>> def faux_time_sleep(amt):
+    ...    global _now
+    ...    _now += amt
+    >>> if isinstance(time,type):
+    ...    time.time = staticmethod(faux_time_time) # Jython
+    ...    time.sleep = faux_time_sleep
+    ... else:
+    ...     time.time = faux_time_time
+    ...     time.sleep = faux_time_sleep
+    >>> def utcnow():
+    ...     return datetime.datetime.fromtimestamp(_now)
+
 Usage
 =====
 
@@ -41,7 +63,7 @@ We wait for some time to pass, record he time, and then make some other changes.
     >>> time.sleep(.01)
 
     >>> import datetime
-    >>> now = datetime.datetime.utcnow()
+    >>> now = utcnow()
     >>> time.sleep(.01)
 
     >>> root = conn.root()
@@ -258,7 +280,7 @@ Note that if you try to open an historical connection to a time in the future,
 you will get an error.
 
     >>> historical_conn = db.open(
-    ...     at=datetime.datetime.utcnow()+datetime.timedelta(1))
+    ...     at=utcnow()+datetime.timedelta(1))
     Traceback (most recent call last):
     ...
     ValueError: cannot open an historical connection in the future.
@@ -293,6 +315,11 @@ memory usage would also be brief and unlikely to overlap.
     >>> db.close()
     >>> db2.close()
 
+.. restore time
+
+    >>> time.time = real_time_time
+    >>> time.sleep = real_time_sleep
+
 .. ......... ..
 .. Footnotes ..
 .. ......... ..