FailsafeThread.h

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//-*-c++-*-
#ifndef INCLUDED_FailsafeThread_h_
#define INCLUDED_FailsafeThread_h_

#include <unistd.h> // for usleep

#include "Shared/TimeET.h"

//! Enforces a timeout on another thread
/*! The target thread needs to either complete execution or set the progressFlag to 'true'
 *  within the specified timeout period.  If the progressFlag is set, it will be cleared at the
 *  end of the timeout, thus requiring the target to re-set within the next timeout period. */
class FailsafeThread : public Thread {
public:
  //! constructor, specify target thread, timeout period, and optionally whether to start now
  FailsafeThread(Thread& th, const TimeET& delayTime, bool autostart=false)
  : Thread(), restartFlag(false), progressFlag(false), delay(useconds_t(delayTime.Value()*1000000)), engageFunc(&Thread::stop), target(th), engaged(false) { if(autostart) start(); }
  
  //! if set to true, the failsafe thread will restart the target if it times out instead of just stopping it
  volatile bool restartFlag;
  
  //! should be set by target thread if it's still making progress and wants another #delay
  volatile bool progressFlag;
  
  //! microseconds to wait between checks on #progressFlag
  /*! Changing this value won't change the @e current timeout period.  You would need to stop and
   *  restart the thread for a change to immediately take effect. */
  volatile useconds_t delay;
  
  //! the function to call on the target thread, defaults to Thread::stop, but Thread::interrupt may be useful
  Thread& (Thread::*engageFunc)();
    
  //! returns true if the FailsafeThread is waiting for the target to stop running
  /*! This is useful for the target thread to check whether it is being stopped from a timeout
   *  (in which case isEngaged() will return true), or if it has been stopped for some other reason. */
  bool isEngaged() const { return engaged; }
  
protected:
  virtual unsigned int runloop() {
    engaged=false;
    // sleep as long as progress is being made
    usleep(delay);
    testCancel();
    while(progressFlag) {
      progressFlag=false;
      usleep(delay);
      testCancel();
    }
    // no more progress -- is the thread still running?
    if(!target.isStarted())
      return -1U; // no, go away
    // yes, stop it
    //std::cout << "failsafe engaged" << std::endl;
    engaged=true;
    (target.*engageFunc)();
    // we killed it... restart it?
    if(!restartFlag)
      return -1U; // no, go away
    // yes, wait for stop to go through, then start it again
    target.join();
    if(!restartFlag) // check again just in case restart was changed while waiting for join()
      return -1U;
    testCancel();
    target.start();
    engaged=false;
    return 0;
  }
  
  //virtual void cancelled() { engaged=false; }
  
  //! the thread being monitored (or at least the one that will be stopped if progressFlag isn't set)
  Thread& target;
  
  //! set to true when FailsafeThread is in the process of stopping (and possibly restarting) the target thread
  bool engaged;
};


/*! @file
 * @brief Describes FailsafeThread, which enforces a timeout on another thread
 * @author Ethan Tira-Thompson (ejt) (Creator)
 */

#endif