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/***************************************************************************
* Copyright (c) 2024 Microsoft Corporation
* Copyright (c) 2025-present Eclipse ThreadX Contributors
*
* This program and the accompanying materials are made available under the
* terms of the MIT License which is available at
* https://opensource.org/licenses/MIT.
*
* SPDX-License-Identifier: MIT
**************************************************************************/
/**************************************************************************/
/**************************************************************************/
/** */
/** NetX Component */
/** */
/** Transmission Control Protocol (TCP) */
/** */
/**************************************************************************/
/**************************************************************************/
#define NX_SOURCE_CODE
/* Include necessary system files. */
#include "nx_api.h"
#include "nx_ip.h"
#ifdef FEATURE_NX_IPV6
#include "nx_ipv6.h"
#endif /* FEATURE_NX_IPV6 */
#include "nx_packet.h"
#include "nx_tcp.h"
/**************************************************************************/
/* */
/* FUNCTION RELEASE */
/* */
/* _nx_tcp_socket_state_transmit_check PORTABLE C */
/* 6.4.3 */
/* AUTHOR */
/* */
/* Yuxin Zhou, Microsoft Corporation */
/* */
/* DESCRIPTION */
/* */
/* This function determines if the new receive window value is large */
/* enough to satisfy a thread suspended trying to send data on the TCP */
/* connection. This is typically called from the ESTABLISHED state. */
/* */
/* INPUT */
/* */
/* socket_ptr Pointer to TCP socket */
/* */
/* OUTPUT */
/* */
/* None */
/* */
/* CALLS */
/* */
/* _nx_tcp_socket_thread_resume Resume suspended thread */
/* */
/* CALLED BY */
/* */
/* _nx_tcp_socket_packet_process Process TCP packet for socket */
/* */
/**************************************************************************/
VOID _nx_tcp_socket_state_transmit_check(NX_TCP_SOCKET *socket_ptr)
{
ULONG tx_window_current;
/* Now check to see if there is a thread suspended attempting to transmit. */
if (socket_ptr -> nx_tcp_socket_transmit_suspension_list)
{
/* Yes, a thread is suspended attempting to transmit when the transmit window
is lower than its request size. Determine if the current transmit window
size can now accommodate the request. */
/* Pick up the min(cwnd, swnd) */
if (socket_ptr -> nx_tcp_socket_tx_window_advertised > socket_ptr -> nx_tcp_socket_tx_window_congestion)
{
tx_window_current = socket_ptr -> nx_tcp_socket_tx_window_congestion;
/* On the first and second duplicate ACKs received, the total FlightSize would
remain less than or equal to cwnd plus 2*SMSS.
Section 3.2, Page 9, RFC5681. */
if ((socket_ptr -> nx_tcp_socket_duplicated_ack_received == 1) ||
(socket_ptr -> nx_tcp_socket_duplicated_ack_received == 2))
{
tx_window_current += (socket_ptr -> nx_tcp_socket_connect_mss << 1);
}
/* Make sure the tx_window_current is less or equal to swnd. */
if (tx_window_current > socket_ptr -> nx_tcp_socket_tx_window_advertised)
{
tx_window_current = socket_ptr -> nx_tcp_socket_tx_window_advertised;
}
}
else
{
tx_window_current = socket_ptr -> nx_tcp_socket_tx_window_advertised;
}
/* Substract any data transmitted but unacked (outstanding bytes) */
if (tx_window_current > socket_ptr -> nx_tcp_socket_tx_outstanding_bytes)
{
tx_window_current -= socket_ptr -> nx_tcp_socket_tx_outstanding_bytes;
}
else /* Set tx_window_current to zero. */
{
tx_window_current = 0;
}
/* Determine if the current transmit window (received from the connected socket)
is large enough to handle the transmit. */
if ((tx_window_current) &&
(socket_ptr -> nx_tcp_socket_transmit_sent_count < socket_ptr -> nx_tcp_socket_transmit_queue_maximum))
{
/* Is NetX set up with a windows update callback? */
if (socket_ptr -> nx_tcp_socket_window_update_notify)
{
/* Yes; Call this function when there is a change in transmit windows size. */
(socket_ptr -> nx_tcp_socket_window_update_notify)(socket_ptr);
}
/* Decrement the suspension count. */
socket_ptr -> nx_tcp_socket_transmit_suspended_count--;
/* Remove the suspended thread from the list. */
_nx_tcp_socket_thread_resume(&(socket_ptr -> nx_tcp_socket_transmit_suspension_list), NX_SUCCESS);
}
}
}
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