bind(0) before probing for random available ports. (#28)

When not using a portserver, assume that the OS knows best. This
should improve reliability.

Though the best thing to do is to use a portserver...

1 files changed, 8 insertions, 8 deletions

diff --git a/src/portpicker.py b/src/portpicker.py
index 4717bbc..fc2825b 100644
--- a/src/portpicker.py
+++ b/src/portpicker.py
@@ -198,14 +198,6 @@ def _pick_unused_port_without_server():  # Protected. pylint: disable=invalid-na
     Raises:
       NoFreePortFoundError: No free port could be found.
     """
-    # Try random ports first.
-    rng = random.Random()
-    for _ in range(10):
-        port = int(rng.randrange(15000, 25000))
-        if is_port_free(port):
-            _random_ports.add(port)
-            return port
-
     # Next, try a few times to get an OS-assigned port.
     # Ambrose discovered that on the 2.6 kernel, calling Bind() on UDP socket
     # returns the same port over and over. So always try TCP first.
@@ -217,6 +209,14 @@ def _pick_unused_port_without_server():  # Protected. pylint: disable=invalid-na
             _random_ports.add(port)
             return port
 
+    # Try random ports as a last resort.
+    rng = random.Random()
+    for _ in range(10):
+        port = int(rng.randrange(15000, 25000))
+        if is_port_free(port):
+            _random_ports.add(port)
+            return port
+
     # Give up.
     raise NoFreePortFoundError()