text: /****************************************************************************
   * net/tcp/tcp_txdrain.c
   *
   *   Copyright (C) 2019 Gregory Nutt. All rights reserved.
   *   Author: Gregory Nutt <gnutt@nuttx.org>
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name NuttX nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /****************************************************************************
   * Included Files
   ****************************************************************************/
  
  #include <nuttx/config.h>
  
  #include <sys/types.h>
  #include <semaphore.h>
  #include <sched.h>
  #include <time.h>
  #include <assert.h>
  #include <errno.h>
  
  #include <nuttx/kmalloc.h>
  #include <nuttx/wqueue.h>
  #include <nuttx/net/net.h>
  
  #include "tcp/tcp.h"
  
  #if defined(CONFIG_NET_TCP_WRITE_BUFFERS) && defined(CONFIG_TCP_NOTIFIER)
  
  /****************************************************************************
   * Private Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: txdrain_worker
   *
   * Description:
   *   Called with the write buffers have all been sent.
   *
   * Input Parameters:
   *   arg     - The notifier entry.
   *
   * Returned Value:
   *   None.
   *
   ****************************************************************************/
  
  static void txdrain_worker(FAR void *arg)
  {
    /* The entire notifier entry is passed to us.  That is because we are
     * responsible for disposing of the entry via kmm_free() when we are
     * finished with it.
     */
  
    FAR struct work_notifier_entry_s *notifier =
      (FAR struct work_notifier_entry_s *)arg;
    FAR sem_t *waitsem;
  
    DEBUGASSERT(notifier != NULL && notifier->info.arg != NULL);
    waitsem = (FAR sem_t *)notifier->info.arg;
  
    /* Free the notifier entry */
  
    kmm_free(notifier);
  
    /* Then just post the semaphore, waking up tcp_txdrain() */
  
    sem_post(waitsem);
  }
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: tcp_txdrain
   *
   * Description:
   *   Wait for all write buffers to be sent (or for a timeout to occur).
   *
   * Input Parameters:
   *   psock   - An instance of the internal socket structure.
   *   abstime - The absolute time when the timeout will occur
   *
   * Returned Value:
   *   Zero (OK) is returned on success; a negated errno value is returned
   *   on any failure.
   *
   ****************************************************************************/
  
  int tcp_txdrain(FAR struct socket *psock,
                  FAR const struct timespec *abstime)
  {
    FAR struct tcp_conn_s *conn;
    sem_t waitsem;
    int ret;
  
    DEBUGASSERT(psock != NULL && psock->s_crefs > 0 && psock->s_conn != NULL);
    DEBUGASSERT(psock->s_type == SOCK_STREAM);
  
    conn = (FAR struct tcp_conn_s *)psock->s_conn;
  
    /* Initialize the wait semaphore */
  
    nxsem_init(&waitsem, 0, 0);
  
    /* The following needs to be done with the network stable */
  
    net_lock();
  
    /* Get a notification when the write buffers are drained */
  
    ret = tcp_writebuffer_notifier_setup(txdrain_worker, conn, &waitsem);
  
    /* The special return value of 0 means that there is no Tx data to be
     * drained.  Otherwise it is a special 'key' that can be used to teardown
     * the notification later
     */
  
    if (ret > 0)
      {
        /* Save the drain key */
  
        int drain_key = ret;
  
        /* Also get a notification if we lose the connection.
         * REVISIT:  This really should not be necessary.  tcp_send() should
         * detect the disconnection event and signal the txdrain but I do not
         * see that TCP disconnection event.  This assures that the txdrain
         * operation will not wait for the full timeout in that case.
         */
  
        ret = tcp_disconnect_notifier_setup(txdrain_worker, conn, &waitsem);
  
         /* Zero is a special value that means that no connection has been
          * established.  Otherwise it is a special 'key' that can be used
          * to teardown the notification later
          */
  
         if (ret > 0)
           {
             /* Save the disconnect key */
  
             int disconn_key = ret;
  
             /* There is pending write data and the socket is connected..
              * wait for it to drain or be be disconnected.
              */
  
            do
              {
                ret = net_timedwait(&waitsem, abstime);
              }
            while (ret == -EINTR);
  
            /* Tear down the disconnect notifier */
  
            tcp_notifier_teardown(disconn_key);
          }
  
        /* Tear down the disconnect notifier */
  
        tcp_notifier_teardown(drain_key);
      }
  
    net_unlock();
    nxsem_destroy(&waitsem);
    return ret;
  }
  
  #endif /* CONFIG_NET_TCP_WRITE_BUFFERS && CONFIG_TCP_NOTIFIER */
  