class TTask: public TNamed

 TTask is a base class that can be used to build a complex tree of Tasks.
 Each TTask derived class may contain other TTasks that can be executed
 recursively, such that a complex program can be dynamically built and executed
 by invoking the services of the top level Task or one of its subtasks.

 Use the TTask::Add function to add a subtask to an existing TTask.
 To execute a TTask, one calls the ExecuteTask function. ExecuteTask will
 call recursively:
     - the TTask::Exec function of the derived class
     - TTask::ExecuteTasks to execute for each task the list of its subtasks.
 If the top level task (see example below) is added to the list of Root
 browsable objects, the tree of tasks can be visualized by the Root browser.
 The browser can be used to start a task, set break points at the beginning
 of a task or when the task has completed. At a breakpoint, data structures
 generated by the execution up this point may be inspected asyncronously
 and then the execution can be resumed by selecting the "Continue" function
 of a task.

 A Task may be active or inactive (controlled by TTask::SetActive).
 When a task is not active, its sub tasks are not executed.

 A TTask tree may be made persistent, saving the status of all the tasks.

 The picture in the Root browser below has been generated by executing
 the following script:

{ //------------------script tasks.C---------------------------
   TTask *aliroot  = new TTask("aliroot","ALICE reconstruction main task");
   TTask *geominit = new TTask("geomInit","Initialize ALICE geometry");
   TTask *matinit  = new TTask("matInit","Initialize ALICE materials");
   TTask *physinit = new TTask("physInit","Initialize Physics processes");
   TTask *tracker  = new TTask("tracker","Track reconstruction manager");
   TTask *tpcrec   = new TTask("tpcrec","TPC reconstruction");
   TTask *itsrec   = new TTask("itsrec","ITS reconstruction");
   TTask *muonrec  = new TTask("muonRec","Muon Reconstruction");
   TTask *phosrec  = new TTask("phosRec","Phos Reconstruction");
   TTask *richrec  = new TTask("richRec","Rich Reconstruction");
   TTask *trdrec   = new TTask("trdRec","TRD Reconstruction");
   TTask *globrec  = new TTask("globRec","Global Track Reconstruction");
   TTask *pstats   = new TTask("printStats","Print Run Statistics");
   TTask *run      = new TTask("run","Process one run");
   TTask *event    = new TTask("event","Process one event");
   aliroot->Add(geominit);
   aliroot->Add(matinit);
   aliroot->Add(physinit);
   aliroot->Add(run);
   run->Add(event);
   event->Add(tracker);
   event->Add(muonrec);
   event->Add(phosrec);
   event->Add(richrec);
   event->Add(trdrec);
   event->Add(globrec);
   tracker->Add(tpcrec);
   tracker->Add(itsrec);
   run->Add(pstats);

   gROOT->GetListOfBrowsables()->Add(aliroot,"aliroot");
   new TBrowser;
} //-------------------------------------------------------------