[DIRMINA-1169] BindException on Java >= 11 due to race condition in AbstractPollingIoAcceptor

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.23, 2.1.6, 2.2.1
• Fix Version/s: 2.1.7, 2.0.24, 2.2.2
• Assignee: Unassigned
• Reporter: Thomas Wolf
• Created: 25/Sep/22 12:53
• Updated: 22/May/23 08:26
• Resolved: 22/May/23 08:26

Description

See also SSHD-1256.

The main acceptor loop does basically (somewhat simplified):

while (selectable) {
  registerHandles(); // Process registration queue: add new sockets (from bind()) to the selector with OP_ACCEPT, fulfills their open futures
  int selected = select();
  if (/* nothing to do */) {
    break; // and end the thread; higher layers will create a new one if needed
  }
  if (selected > 0) {
    processHandles(selectedHandles()); // Handle and hand off new connections
  }
  unregisterHandles(); // Process cancel queue: cancel SelectionKey, close ServerSocketChannel, fulfill the cancel future
}

With Java 11, unbinding a ServerSocketChannel changed:

• JDK-8214430
• Java 11 Release Notes

Essentially the unbind gives up the socket only at the next select() call. This causes two problems in Apache MINA's acceptor:

• The unbind future is set "done" before the socket is actually released.
• If a new binding for one of the unbound sockets is registered before that select() has been done, registerHandles() gets a BindException ("address already in use").

So for Java >= 11, the code must ensure that there is a select() between processing unbindings and processing new bindings, and the unbind futures must be set "done" only after that select().

Issue Links

• causes: SSHD-1256 PortForwardingTest.testRemoteForwardingSecondTimeInSameSession sometimes fails in Github CI