main-attribute-value.cc

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/*
 * Copyright (c) 2008 University of Washington
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Tom Henderson <tomh@tomh.org>
 */
 
#include "ns3/command-line.h"
#include "ns3/config.h"
#include "ns3/drop-tail-queue.h"
#include "ns3/log.h"
#include "ns3/node.h"
#include "ns3/point-to-point-net-device.h"
#include "ns3/pointer.h"
#include "ns3/ptr.h"
#include "ns3/queue.h"
#include "ns3/simulator.h"
#include "ns3/string.h"
#include "ns3/uinteger.h"
 
using namespace ns3;
 
NS_LOG_COMPONENT_DEFINE("AttributeValueSample");
 
//
// This is a basic example of how to use the attribute system to
// set and get a value in the underlying system; namely, the maximum
// size of the FIFO queue in the PointToPointNetDevice
//
 
int
main(int argc, char* argv[])
{
    LogComponentEnable("AttributeValueSample", LOG_LEVEL_INFO);
 
    // Queues in ns-3 are objects that hold items (other objects) in
    // a queue structure.  The C++ implementation uses templates to
    // allow queues to hold various types of items, but the most
    // common is a pointer to a packet (Ptr<Packet>).
    //
    // The maximum queue size can either be enforced in bytes ('b') or
    // packets ('p').  A special type called the ns3::QueueSize can
    // hold queue size values in either unit (bytes or packets).  The
    // DropTailQueue<Packet> class has a MaxSize attribute that can
    // be set to a QueueSize.
 
    // By default, the MaxSize attribute has a value of 100 packets ('100p')
    // (this default can be observed in the function DropTail<Item>::GetTypeId)
    //
    // Here, we set it to 80 packets.  We could use one of two value types:
    // a string-based value or a QueueSizeValue value
    Config::SetDefault("ns3::DropTailQueue<Packet>::MaxSize", StringValue("80p"));
    // The below function call is redundant
    Config::SetDefault("ns3::DropTailQueue<Packet>::MaxSize",
                       QueueSizeValue(QueueSize(QueueSizeUnit::PACKETS, 80)));
 
    // Allow the user to override any of the defaults and the above
    // SetDefaults() at run-time, via command-line arguments
    // For example, via "--ns3::DropTailQueue<Packet>::MaxSize=80p"
    CommandLine cmd(__FILE__);
    // This provides yet another way to set the value from the command line:
    cmd.AddValue("maxSize", "ns3::DropTailQueue<Packet>::MaxSize");
    cmd.Parse(argc, argv);
 
    // Now, we will create a few objects using the low-level API
    Ptr<Node> n0 = CreateObject<Node>();
 
    Ptr<PointToPointNetDevice> net0 = CreateObject<PointToPointNetDevice>();
    n0->AddDevice(net0);
 
    Ptr<Queue<Packet>> q = CreateObject<DropTailQueue<Packet>>();
    net0->SetQueue(q);
 
    // At this point, we have created a single node (Node 0) and a
    // single PointToPointNetDevice (NetDevice 0) and added a
    // DropTailQueue to it.
 
    // Now, we can manipulate the MaxSize value of the already
    // instantiated DropTailQueue.  Here are various ways to do that.
 
    // We assume that a smart pointer (Ptr) to a relevant network device
    // is in hand; here, it is the net0 pointer.
 
    // 1.  Pointer-based access
    //
    // One way to change the value is to access a pointer to the
    // underlying queue and modify its attribute.
    //
    // First, we observe that we can get a pointer to the (base class)
    // queue via the PointToPointNetDevice attributes, where it is called
    // TxQueue
    PointerValue ptr;
    net0->GetAttribute("TxQueue", ptr);
    Ptr<Queue<Packet>> txQueue = ptr.Get<Queue<Packet>>();
 
    // Using the GetObject function, we can perform a safe downcast
    // to a DropTailQueue
    Ptr<DropTailQueue<Packet>> dtq = txQueue->GetObject<DropTailQueue<Packet>>();
    NS_ASSERT(dtq);
 
    // Next, we can get the value of an attribute on this queue
    // We have introduced wrapper "Value" classes for the underlying
    // data types, similar to Java wrappers around these types, since
    // the attribute system stores values and not disparate types.
    // Here, the attribute value is assigned to a QueueSizeValue, and
    // the Get() method on this value produces the (unwrapped) QueueSize.
    QueueSizeValue limit;
    dtq->GetAttribute("MaxSize", limit);
    NS_LOG_INFO("1.  dtq limit: " << limit.Get());
 
    // Note that the above downcast is not really needed; we could have
    // done the same using the Ptr<Queue> even though the attribute
    // is a member of the subclass
    txQueue->GetAttribute("MaxSize", limit);
    NS_LOG_INFO("2.  txQueue limit: " << limit.Get());
 
    // Now, let's set it to another value (60 packets).  Let's also make
    // use of the StringValue shorthand notation to set the size by
    // passing in a string (the string must be a positive integer suffixed
    // by either the 'p' or 'b' character).
    txQueue->SetAttribute("MaxSize", StringValue("60p"));
    txQueue->GetAttribute("MaxSize", limit);
    NS_LOG_INFO("3.  txQueue limit changed: " << limit.Get());
 
    // 2.  Namespace-based access
    //
    // An alternative way to get at the attribute is to use the configuration
    // namespace.  Here, this attribute resides on a known path in this
    // namespace; this approach is useful if one doesn't have access to
    // the underlying pointers and would like to configure a specific
    // attribute with a single statement.
    Config::Set("/NodeList/0/DeviceList/0/TxQueue/MaxSize", StringValue("25p"));
    txQueue->GetAttribute("MaxSize", limit);
    NS_LOG_INFO("4.  txQueue limit changed through namespace: " << limit.Get());
 
    // we could have also used wildcards to set this value for all nodes
    // and all net devices (which in this simple example has the same
    // effect as the previous Set())
    Config::Set("/NodeList/*/DeviceList/*/TxQueue/MaxSize", StringValue("15p"));
    txQueue->GetAttribute("MaxSize", limit);
    NS_LOG_INFO("5.  txQueue limit changed through wildcarded namespace: " << limit.Get());
 
    Simulator::Destroy();
 
    return 0;
}