omnet++：tictoc例子6的函数解读：scheduleAt

//
// This file is part of an OMNeT++/OMNEST simulation example.
//
// Copyright (C) 2003-2015 Andras Varga
//
// This file is distributed WITHOUT ANY WARRANTY. See the file
// `license' for details on this and other legal matters.
//

#include <stdio.h>
#include <string.h>
#include <omnetpp.h>

using namespace omnetpp;

/**
 * In the previous models, `tic' and `toc' immediately sent back the
 * received message. Here we'll add some timing: tic and toc will hold the
 * message for 1 simulated second before sending it back. In OMNeT++
 * such timing is achieved by the module sending a message to itself.
 * Such messages are called self-messages (but only because of the way they
 * are used, otherwise they are completely ordinary messages) or events.
 * Self-messages can be "sent" with the scheduleAt() function, and you can
 * specify when they should arrive back at the module.
 *
 * We leave out the counter, to keep the source code small.
 */
class Txc6 : public cSimpleModule
{
  private:
    cMessage *event;  // pointer to the event object which we'll use for timing
    cMessage *tictocMsg;  // variable to remember the message until we send it back

  public:
    Txc6();
    virtual ~Txc6();

  protected:
    virtual void initialize() override;
    virtual void handleMessage(cMessage *msg) override;
};

Define_Module(Txc6);

Txc6::Txc6()
{
    // Set the pointer to nullptr, so that the destructor won't crash
    // even if initialize() doesn't get called because of a runtime
    // error or user cancellation during the startup process.
    event = tictocMsg = nullptr;
}

Txc6::~Txc6()
{
    // Dispose of dynamically allocated the objects
    cancelAndDelete(event);
    delete tictocMsg;
}

void Txc6::initialize()
{
    // Create the event object we'll use for timing -- just any ordinary message.
    event = new cMessage("event");//初始化event内容，任何的都可以

    // No tictoc message yet.
    tictocMsg = nullptr;

    if (strcmp("tic", getName()) == 0) {
        // We don't start right away, but instead send an message to ourselves
        // (a "self-message") -- we'll do the first sending when it arrives
        // back to us, at t=5.0s simulated time.
        EV << "Scheduling first send to t=5.0s\n";
        tictocMsg = new cMessage("tictocMsg");
        scheduleAt(5.0, event);//此函数的说明在下图，会在计时器到时调用handleMessage或recive函数接收event消息，此处计时器设定是5秒，到时接收的消息就是event指针内容
    }
}

void Txc6::handleMessage(cMessage *msg)
{
    // There are several ways of distinguishing messages, for example by message
    // kind (an int attribute of cMessage) or by class using dynamic_cast
    // (provided you subclass from cMessage). In this code we just check if we
    // recognize the pointer, which (if feasible) is the easiest and fastest
    // method.
    if (msg == event) {
        // The self-message arrived, so we can send out tictocMsg and nullptr out
        // its pointer so that it doesn't confuse us later.
        EV << "Wait period is over, sending back message\n";
        send(tictocMsg, "out");//从out端口将缓存中的消息发送，
        tictocMsg = nullptr; //清空接收消息的缓存，等待下次接收消息
    }
    else {
        // If the message we received is not our self-message, then it must
        // be the tic-toc message arriving from our partner. We remember its
        // pointer in the tictocMsg variable, then schedule our self-message
        // to come back to us in 1s simulated time.
        EV << "Message arrived, starting to wait 1 sec...\n";
        tictocMsg = msg;//接收消息到缓存
        scheduleAt(simTime()+1.0, event);//设定计时器为当前模拟时刻+1秒；即一秒后会收到event                    
                                           再经过handleMessage处理。
    }
}