path: root/pflocal/connq.c

/* Listen queue functions

   Copyright (C) 1995, 1996 Free Software Foundation, Inc.

   Written by Miles Bader <miles@gnu.ai.mit.edu>

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2, or (at
   your option) any later version.

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */

#include <cthreads.h>

#include "connq.h"

/* A queue for queueing incoming connections.  */
struct connq
{
  /* True if all connection requests should be treated as non-blocking.  */
  int noqueue;

  /* The connection request queue.  */
  struct connq_request **queue;
  unsigned length;
  /* Head is the position in QUEUE of the first request, and TAIL is the
     first free position in the queue.  If HEAD == TAIL, then the queue is
     empty.  Starting at HEAD, successive positions can be calculated by
     using qnext().  */
  unsigned head, tail;

  /* Threads that have done an accept on this queue wait on this condition.  */
  struct condition listeners;
  unsigned num_listeners;

  struct mutex lock;
};

/* Returns the position CQ's queue after POS.  */
static inline unsigned
qnext (struct connq *cq, unsigned pos)
{
  return (pos + 1 == cq->length) ? 0 : pos + 1;
}

/* ---------------------------------------------------------------- */

/* A data block allocated by a thread waiting on a connq, which is used to
   get information from and to the thread.  */
struct connq_request
{
  /* The socket that's waiting to connect.  */
  struct sock *sock;

  /* What the waiting thread blocks on.  */
  struct condition signal;
  struct mutex lock;

  /* Set to true when this request has been dealt with, to guard against
     spurious conditions being signaled.  */
  int completed;

  /* After the waiting thread is unblocked, this is the result, either 0 if
     SOCK has been connected, or an error.  */
  error_t err;
};

static inline void
connq_request_init (struct connq_request *req, struct sock *sock)
{
  req->err = 0;
  req->sock = sock;
  req->completed = 0;
  condition_init (&req->signal);
  mutex_init (&req->lock);
}

/* ---------------------------------------------------------------- */

/* Create a new listening queue, returning it in CQ.  The resulting queue
   will be of zero length, that is it won't allow connections unless someone
   is already listening (change this with connq_set_length).  */
error_t
connq_create (struct connq **cq)
{
  struct connq *new = malloc (sizeof (struct connq));

  if (!new)
    return ENOMEM;

  new->noqueue = 1;		/* By default, don't queue requests.  */
  new->length = 0;
  new->head = new->tail = 0;
  new->queue = NULL;
  new->num_listeners = 0;

  mutex_init (&new->lock);
  condition_init (&new->listeners);

  *cq = new;
  return 0;
}

/* Destroy a queue.  */
void
connq_destroy (struct connq *cq)
{
  /* Everybody in the queue should hold a reference to the socket
     containing the queue.  */
  assert (cq->length == 0);
  /* Nevertheless, malloc(0) or realloc(0) might allocate some small
     space.  */
  if (cq->queue)
    free (cq->queue);
  free (cq);
}

/* ---------------------------------------------------------------- */

/* Wait for a connection attempt to be made on CQ, and return the connecting
   socket in SOCK, and a request tag in REQ.  If REQ is NULL, the request is
   left in the queue, otherwise connq_request_complete must be called on REQ
   to allow the requesting thread to continue.  If NOBLOCK is true,
   EWOULDBLOCK is returned when there are no immediate connections
   available. */
error_t 
connq_listen (struct connq *cq, int noblock,
	      struct connq_request **req, struct sock **sock)
{
  mutex_lock (&cq->lock);

  if (noblock && cq->head == cq->tail)
    {
      mutex_unlock (&cq->lock);	  
      return EWOULDBLOCK;
    }

  cq->num_listeners++;

  while (cq->head == cq->tail)
    if (hurd_condition_wait (&cq->listeners, &cq->lock))
      {
	cq->num_listeners--;
	mutex_unlock (&cq->lock);	  
	return EINTR;
      }

  if (req != NULL)
    /* Dequeue the next request, if desired.  */
    {
      *req = cq->queue[cq->head];
      cq->head = qnext (cq, cq->head);
      if (sock != NULL)
	*sock = (*req)->sock;
    }

  cq->num_listeners--;

  mutex_unlock (&cq->lock);

  return 0;    
}

/* Return the error code ERR to the thread that made the listen request REQ,
   returned from a previous connq_listen.  */
void
connq_request_complete (struct connq_request *req, error_t err)
{
  mutex_lock (&req->lock);
  req->err = err;
  req->completed = 1;
  condition_signal (&req->signal);
  mutex_unlock (&req->lock);
}

/* Try to connect SOCK with the socket listening on CQ.  If NOBLOCK is true,
   then return EWOULDBLOCK immediately when there are no immediate
   connections available.  Neither SOCK nor CQ should be locked.  */
error_t
connq_connect (struct connq *cq, int noblock, struct sock *sock)
{
  error_t err = 0;
  unsigned next;

  mutex_lock (&cq->lock);

  /* Check for listeners after we've locked CQ for good.  */
  if ((noblock || cq->noqueue) && cq->num_listeners == 0)
    {
      mutex_unlock (&cq->lock);
      return EWOULDBLOCK;
    }

  next = qnext (cq, cq->tail);
  if (next == cq->tail)
    /* The queue is full.  */
    err = ECONNREFUSED;
  else
    {
      struct connq_request req;

      connq_request_init (&req, sock);

      cq->queue[cq->tail] = &req;
      cq->tail = next;

      /* Hold REQ.LOCK before we signal the condition so that we're sure
	 to be woken up.  */
      mutex_lock (&req.lock);
      condition_signal (&cq->listeners);
      mutex_unlock (&cq->lock);

      while (!req.completed)
	condition_wait (&req.signal, &req.lock);
      err = req.err;

      mutex_unlock (&req.lock);
    }

  return err;
}

/* `Compresses' CQ, by removing any NULL entries.  CQ should be locked.  */
static void
connq_compress (struct connq *cq)
{
  unsigned pos;
  unsigned comp_tail = cq->head;

  /* Now compress the queue to remove any null entries we put in.  */
  for (pos = cq->head; pos != cq->tail; pos = qnext (cq, pos))
    if (cq->queue[pos] != NULL)
      /* This position has a non-NULL request, so move it to the end of the
	 compressed queue.  */
      {
	cq->queue[comp_tail] = cq->queue[pos];
	comp_tail = qnext (cq, comp_tail);
      }

  /* Move back tail to only include what we kept in the queue.  */
  cq->tail = comp_tail;
}

/* Set CQ's queue length to LENGTH.  Any sockets already waiting for a
   connections that are past the new length will fail with ECONNREFUSED.  */
error_t 
connq_set_length (struct connq *cq, int length)
{
  mutex_lock (&cq->lock);

  if (length > cq->length)
    /* Growing the queue is simple... */
    cq->queue = realloc (cq->queue, sizeof (struct connq_request *) * length);
  else
    /* Shrinking it less so.  */
    {
      int i;
      struct connq_request **new_queue =
	malloc (sizeof (struct connq_request *) * length);

      for (i = 0; i < cq->length && cq->head != cq->tail; i++)
	{
	  if (i < length)
	    /* Keep this connect request in the queue.  */
	    new_queue[length - i] = cq->queue[cq->head];
	  else
	    /* Punt this one.  */
	    connq_request_complete (cq->queue[cq->head], ECONNREFUSED);
	  cq->head = qnext (cq, cq->head);
	}

      free (cq->queue);
      cq->queue = new_queue;
    }

  cq->noqueue = 0;		/* Turn on queueing.  */

  mutex_unlock (&cq->lock);

  return 0;
}