#909 ✓resolved
Tim Stone

JPDA port checking can fail on some versions of Windows

Reported by Tim Stone | June 14th, 2011 @ 02:45 AM | in 1.2.4 (closed)

Framework version: 1.2.1 Platform: Windows 7 x64

Reproduction steps:

On a recent Windows system (Server 2003/2008, Vista, or 7):

  • Start one Play site on port x in dev mode
  • Start another Play site on port y in dev mode
  • The second site will fail to launch with the error:

    ERROR: transport error 202: bind failed: Address already in use
    ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510)


application.py tests for this condition to reassign a random port number for JDPA, but it's failing to do so here.

The listed versions of Windows include "Enhanced Socket Security", which allows the same port to be bound on both a specific address and the wildcard address simultaneously. In this case, JPDA binds to the wildcard address, so no exception is thrown on Windows when the Python script checks to see if the port is bound on This allows the script to continue on with the default JDPA port, and when the JVM is started the process throws an error. However, if the hosts are changed to be the same, the startup script functions as intended and both sites can run at the same time.

To directly demonstrate this issue, you can try the following Python code:

import socket
a = socket.socket()
b = socket.socket()
c = socket.socket()
a.bind(('', 20202))
b.bind(('', 20202))
# No error on recent Windows versions
c.bind(('', 20202))
# socket.error

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