test_events.cpp

This is an example on how to use events

This example shows the basic operation with events and the most important feature, which is the wait() function. This example mainly sets the event several times and waits for it. Most of the times the wait function return immediatelly after being called, and some other times, a timeout error is generated.

In this case the name of the event is just informative, but when the CEventServer class is used, this name is used as a unique identifier of each event.

The output of this example program should be something like this:

* Event identifier: test_event1
* Number of instances of the event: 1
* Number of instances of the event: 1
* [Exception caught] - [CEvent class] - The maximum time to wait for the event activation has ellapsed - test_event1
* Number of instances of the event: 3
* Number of instances of the event: 2
* Number of instances of the event: 1
* Number of instances if the event: 0
* 

Before the timeout exception, the program halts for about 1 second, which is the desired timeout. Several error may be thrown by the CEvent class:

• The maximum time to wait for an event ellapsed.

// Copyright (C) 2009-2010 Institut de Robòtica i Informàtica Industrial, CSIC-UPC.
// Author Sergi Hernandez  (shernand@iri.upc.edu)
// All rights reserved.
//
// This file is part of iriutils
// iriutils is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#include "eventexceptions.h"
#include "event.h"
#include <stdio.h>
#include <unistd.h>
#include <iostream>

int main(int argc, char *argv[])
{
  std::string event_id="";
  int num=0;
  CEvent Event("test_event1");

  event_id=Event.get_id();
  std::cout << "Event identifier: " << event_id << std::endl;
  // activate the event once
  Event.set();
  num=Event.get_num_activations();
  // the expected value is 1
  std::cout << "Number of instances of the event: " << num << std::endl;
  // wait for it to be signaled (this function returns immediatelly)
  Event.wait(1000000);
  // activate the event again
  Event.set();
  num=Event.get_num_activations();
  std::cout << "Number of instances of the event: " << num << std::endl;
  // reset the event
  Event.reset();
  // wait for the event to be signales. This function will get blocked until
  // the timeout expires.
  try {
    Event.wait(1000000);
  }catch(CEventTimeoutException& e){
    std::cout << e.what() << std::endl;
  }catch(CException& e){
    std::cout << e.what() << std::endl;
    return 0;
  }
  // activate the event several times
  Event.set();
  Event.set();
  Event.set();
  num=Event.get_num_activations();
  // the expected value is 3
  std::cout << "Number of instances of the event: " << num << std::endl;
  Event.reset();
  num=Event.get_num_activations();
  // the expected value is 2
  std::cout << "Number of instances of the event: " << num << std::endl;
  Event.wait(-1);
  num=Event.get_num_activations();
  // the expected value is 1
  std::cout << "Number of instances of the event: " << num << std::endl;
  if(Event.is_set())
  {
    Event.wait(-1);
  }
  num=Event.get_num_activations();
  // the expected value is 0
  std::cout << "Number of instances if the event: " << num << std::endl;
  if(Event.is_set())
  {
    Event.wait(-1);
  }

  return 0;
}