issue #155: allocate child IDs in batches of 1000.

Avoids a roundtrip for every fork.

mitogen/master.py

@@ -724,16 +724,25 @@ class IdAllocator(object):
         finally:
             self.lock.release()
 
+    def allocate_block(self):
+        self.lock.acquire()
+        try:
+            id_ = self.next_id
+            self.next_id += 1000
+            return id_, id_ + 1000
+        finally:
+            self.lock.release()
+
     def on_allocate_id(self, msg):
         if msg == mitogen.core._DEAD:
             return
 
-        id_ = self.allocate()
+        id_, last_id = self.allocate_block()
         requestee = self.router.context_by_id(msg.src_id)
         allocated = self.router.context_by_id(id_, msg.src_id)
 
-        LOG.debug('%r: allocating %r to %r', self, allocated, requestee)
-        msg.reply(id_)
+        LOG.debug('%r: allocating [%r..%r) to %r', self, allocated, requestee)
+        msg.reply((id_, last_id))
 
         LOG.debug('%r: publishing route to %r via %r', self,
                   allocated, requestee)

mitogen/parent.py

@@ -37,6 +37,7 @@ import socket
 import sys
 import termios
 import textwrap
+import threading
 import time
 import zlib
 
@@ -423,12 +424,24 @@ class Stream(mitogen.core.Stream):
 class ChildIdAllocator(object):
     def __init__(self, router):
         self.router = router
+        self.lock = threading.Lock()
+        self.it = iter(xrange(0))
 
     def allocate(self):
-        master = mitogen.core.Context(self.router, 0)
-        return master.send_await(
-            mitogen.core.Message(dst_id=0, handle=mitogen.core.ALLOCATE_ID)
-        )
+        self.lock.acquire()
+        try:
+            for id_ in self.it:
+                return id_
+
+            master = mitogen.core.Context(self.router, 0)
+            start, end = master.send_await(
+                mitogen.core.Message(dst_id=0, handle=mitogen.core.ALLOCATE_ID)
+            )
+            self.it = iter(xrange(start, end))
+        finally:
+            self.lock.release()
+
+        return self.allocate()
 
 
 class Router(mitogen.core.Router):

tests/id_allocation_test.py

@@ -8,8 +8,20 @@ import id_allocation
 class SlaveTest(testlib.RouterMixin, testlib.TestCase):
     def test_slave_allocates_id(self):
         context = self.router.local()
+        # Master's allocator named the context 1.
+        self.assertEquals(1, context.context_id)
+
+        # First call from slave allocates a block (2..1001)
+        id_ = context.call(id_allocation.allocate_an_id)
+        self.assertEqual(id_, 2)
+
+        # Second call from slave allocates from block (3..1001)
         id_ = context.call(id_allocation.allocate_an_id)
-        self.assertEqual(id_, self.router.id_allocator.next_id - 1)
+        self.assertEqual(id_, 3)
+
+        # Subsequent master allocation does not collide
+        c2 = self.router.local()
+        self.assertEquals(1002, c2.context_id)
 
 
 if __name__ == '__main__':