source: src/Patterns/Observer.cpp@ 5c8592

/*
 * Observer.cpp
 *
 *  Created on: Jan 19, 2010
 *      Author: crueger
 */

#include "Observer.hpp"


#include <iostream>
#include <cassert>

using namespace std;

/****************** Static stuff for the observer mechanism ************/

// All infrastructure for the observer-pattern is bundled at a central place
// this is more efficient if many objects can be observed (inherit from observable)
// but only few are actually coupled with observers. E.g. TMV has over 500.000 Atoms,
// which might become observable. Handling Observerable infrastructure in each of
// these would use memory for each atom. By handling Observer-infrastructure
// here we only need memory for objects that actually are observed.
// See [Gamma et al, 1995] p. 297

map<Observable*, int> Observable::depth;  //!< Map of Observables to the depth of the DAG of Observers
map<Observable*,multimap<int,Observer*>*> Observable::callTable; //!< Table for each Observable of all its Observers
set<Observable*> Observable::busyObservables; //!< Set of Observables that are currently busy notifying their sign-on'ed Observers

/** Attaching Sub-observables to Observables.
 * Increases entry in Observable::depth for this \a *publisher by one.
 *
 * The two functions \sa start_observer_internal() and \sa finish_observer_internal()
 * have to be used together at all time. Never use these functions directly
 * START_OBSERVER and FINISH_OBSERVER also construct a bogus while(0) loop
 * thus producing compiler-errors whenever only one is used.
 * \param *publisher reference of sub-observable
 */
void Observable::start_observer_internal(Observable *publisher){
  // increase the count for this observable by one
  // if no entry for this observable is found, an new one is created
  // by the STL and initialized to 0 (see STL documentation)
  depth[publisher]++;
}

/** Detaching Sub-observables from Observables.
 * Decreases entry in Observable::depth for this \a *publisher by one. If zero, we
 * start notifying all our Observers.
 *
 * The two functions start_observer_internal() and finish_observer_internal()
 * have to be used together at all time. Never use these functions directly
 * START_OBSERVER and FINISH_OBSERVER also construct a bogus while(0) loop
 * thus producing compiler-errors whenever only one is used.
 * \param *publisher reference of sub-observable
 */
void Observable::finish_observer_internal(Observable *publisher){
  // decrease the count for this observable
  // if zero is reached all observed blocks are done and we can
  // start to notify our observers
  if(--(depth[publisher])){}
  else{
    publisher->notifyAll();
    // this item is done, so we don't have to keep the count with us
    // save some memory by erasing it
    depth.erase(publisher);
  }
}

/** Constructor for Observable Protector.
 * Basically, calls start_observer_internal(). Hence use this class instead of
 * calling the function directly.
 *
 * \param *protege Observable to be protected.
 */
Observable::_Observable_protector::_Observable_protector(Observable *_protege) :
  protege(_protege)
{
  start_observer_internal(protege);
}

/** Destructor for Observable Protector.
 * Basically, calls finish_observer_internal(). Hence use this class instead of
 * calling the function directly.
 *
 * \param *protege Observable to be protected.
 */
Observable::_Observable_protector::~_Observable_protector()
{
  finish_observer_internal(protege);
}

/************* Notification mechanism for observables **************/

/** Notify all Observers of changes.
 * Puts \a *this into Observable::busyObservables, calls Observer::update() for all in callee_t
 * and removes from busy list.
 */
void Observable::notifyAll() {
  // we are busy notifying others right now
  // add ourselves to the list of busy subjects to enable circle detection
  busyObservables.insert(this);
  // see if anyone has signed up for observation
  // and call all observers
  if(callTable.count(this)) {
    // elements are stored sorted by keys in the multimap
    // so iterating over it gives us a the callees sorted by
    // the priorities
    callees_t *callees = callTable[this];
    callees_t::iterator iter;
    for(iter=callees->begin();iter!=callees->end();iter++){
      (*iter).second->update(this);
    }
  }
  // done with notification, we can leave the set of busy subjects
  busyObservables.erase(this);
}

/** Handles passing on updates from sub-Observables.
 * Mimicks basically the Observer::update() function.
 *
 * \param *publisher The \a *this we observe.
 */
void Observable::update(Observable *publisher) {
  // circle detection
  if(busyObservables.find(this)!=busyObservables.end()) {
    // somehow a circle was introduced... we were busy notifying our
    // observers, but still we are called by one of our sub-Observables
    // we cannot be sure observation will still work at this point
    cerr << "Circle detected in observation-graph." << endl;
    cerr << "Observation-graph always needs to be a DAG to work correctly!" << endl;
    cerr << "Please check your observation code and fix this!" << endl;
    return;
  }
  else {
    // see if we are in the process of changing ourselves
    // if we are changing ourselves at the same time our sub-observables change
    // we do not need to publish all the changes at each time we are called
    if(depth.find(this)==depth.end()) {
      notifyAll();
    }
  }
}

/** Sign on an Observer to this Observable.
 * Puts \a *target into Observable::callTable list.
 * \param *target Observer
 * \param priority number in [-20,20]
 */
void Observable::signOn(Observer *target,int priority) {
  assert(priority>=-20 && priority<=+20 && "Priority out of range [-20:+20]");
  bool res = false;
  callees_t *callees = 0;
  if(callTable.count(this)){
    callees = callTable[this];
  }
  else {
    callees = new multimap<int,Observer*>;
    callTable.insert(pair<Observable*,callees_t*>(this,callees));
  }

  callees_t::iterator iter;
  for(iter=callees->begin();iter!=callees->end();iter++){
    res |= ((*iter).second == target);
  }
  if(!res)
    callees->insert(pair<int,Observer*>(priority,target));
}

/** Sign off an Observer from this Observable.
 * Removes \a *target from Observable::callTable list.
 * \param *target Observer
 */
void Observable::signOff(Observer *target) {
  assert(callTable.count(this) && "SignOff called for an Observable without Observers.");
  callees_t *callees = callTable[this];
  callees_t::iterator iter;
  callees_t::iterator deliter;
  for(iter=callees->begin();iter!=callees->end();) {
    deliter=iter++;
    if((*deliter).second == target)
      callees->erase(deliter);
  }
  if(callees->empty()){
    callTable.erase(this);
    delete callees;
  }
}

/** Handles sub-observables that just got killed
 *  when an sub-observerable dies we usually don't need to do anything
 *  \param *publisher Sub-Observable.
 */
void Observable::subjectKilled(Observable *publisher){
}

/** Constructor for class Observable.
 */
Observable::Observable()
{}

/** Destructor for class Observable.
 * When an observable is deleted, we let all our observers know. \sa Observable::subjectKilled().
 */
Observable::~Observable()
{
  if(callTable.count(this)) {
    // delete all entries for this observable
    callees_t *callees = callTable[this];
    callees_t::iterator iter;
    for(iter=callees->begin();iter!=callees->end();iter++){
      (*iter).second->subjectKilled(this);
    }
    callTable.erase(this);
    delete callees;
  }
}

/** Constructor for class Observer.
 */
Observer::Observer()
{}

/** Destructor for class Observer.
 */
Observer::~Observer()
{}