yet faster web2py_uuid by caching urandom results

VERSION

@@ -1 +1 @@
-Version 2.0.9 (2012-09-29 17:16:28) dev
+Version 2.0.9 (2012-09-29 17:56:36) dev

gluon/utils.py

@@ -10,6 +10,7 @@ This file specifically includes utilities for security.
 """
 
 import string
+import threading
 import struct
 import hashlib
 import hmac
@@ -110,6 +111,7 @@ def initialize_urandom():
     random.seed(node_id + microseconds)
     try:
         os.urandom(1)
+        have_urandom = True
         try:
             # try to add process-specific entropy
             frandom = open('/dev/urandom','wb')
@@ -121,13 +123,31 @@ def initialize_urandom():
             # works anyway
             pass
     except NotImplementedError:
+        have_urandom = False
         logger.warning(
 """Cryptographically secure session management is not possible on your system because
 your system does not provide a cryptographically secure entropy source.
 This is not specific to web2py; consider deploying on a different operating system.""")
-    return ctokens
-CTOKENS = initialize_urandom()
-UNPACKED_CTOKENS = struct.unpack('=QQ',string.join((chr(x) for x in CTOKENS),''))
+    unpacked_ctokens = struct.unpack('=QQ',string.join(
+            (chr(x) for x in ctokens),''))
+    return unpacked_ctokens, have_urandom
+UNPACKED_CTOKENS, HAVE_URANDOM = initialize_urandom()
+
+def fast_urandom16(urandom=[], locker = threading.RLock()):
+    """
+    this is 4x faster than calling os.urandom(16) and prevents
+    the "too many files open" issue with concurrent access to os.urandom()
+    """
+    try:
+        return urandom.pop()
+    except IndexError:
+        try:
+            locker.acquire()
+            ur = os.urandom(16*1024)
+            urandom += [ur[i:i+16] for i in xrange(16,1024*16,16)]
+            return ur[0:16]
+        finally:
+            locker.release()
 
 def web2py_uuid(ctokens=UNPACKED_CTOKENS):
     """
@@ -139,12 +159,12 @@ def web2py_uuid(ctokens=UNPACKED_CTOKENS):
     """
     rand_longs = struct.unpack('=QQ', bytes(bytearray(
                 random.randrange(256) for i in xrange(16))))
-    try:
-        urand_longs = struct.unpack('=QQ', os.urandom(16))
-        byte_s = struct.pack('=QQ', 
+    if HAVE_URANDOM:
+        urand_longs = struct.unpack('=QQ', fast_urandom16())
+        byte_s = struct.pack('=QQ',
                              rand_longs[0]^urand_longs[0]^ctokens[0], 
                              rand_longs[1]^urand_longs[1]^ctokens[1])
-    except NotImplementedError:
+    else:
         byte_s = struct.pack('=QQ', 
                              rand_longs[0]^ctokens[0], 
                              rand_longs[1]^ctokens[1])