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[thirdparty/pdns.git] / pdns / delaypipe.hh

/*
 * This file is part of PowerDNS or dnsdist.
 * Copyright -- PowerDNS.COM B.V. and its contributors
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * In addition, for the avoidance of any doubt, permission is granted to
 * link this program with OpenSSL and to (re)distribute the binaries
 * produced as the result of such linking.
 *
 * 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#pragma once
#include <map>
#include <time.h>
#include <thread>

/**
   General idea: many threads submit work to this class, but only one executes it. The work should therefore be entirely trivial.
   The implementation is that submitter threads create an object that represents the work, and it gets sent over a pipe 
   to the worker thread.

   The worker thread meanwhile listens on this pipe (non-blocking), with a delay set to the next object that needs to be executed.
   If meanwhile new work comes in, all objects who's time has come are executed, a new sleep time is calculated.
*/


/* ObjectPipe facilitates the type-safe passing of types over a pipe */

template<class T>
class ObjectPipe
{
public:
  ObjectPipe();
  ~ObjectPipe();
  void write(T& t);
  bool read(T* t); // returns false on EOF
  int readTimeout(T* t, double msec); //!< -1 is timeout, 0 is no data, 1 is data. msec<0 waits infinitely wrong. msec==0 = undefined
  void close(); 
private:
  int d_fds[2];
};

template<class T>
class DelayPipe
{
public:
  DelayPipe();
  ~DelayPipe();
  void submit(T& t, int msec); //!< don't try for more than 4294 msec

private:
  void worker();
  struct Combo
  {
    T what;
    struct timespec when;
  };

  double tsdelta(const struct timespec& a, const struct timespec& b) // read as a-b
  {
    return 1.0*(a.tv_sec-b.tv_sec)+1.0*(a.tv_nsec-b.tv_nsec)/1000000000.0;
  }

  ObjectPipe<Combo> d_pipe;
  struct tscomp {
    bool operator()(const struct timespec& a, const struct timespec& b) const
    {
      return std::tie(a.tv_sec, a.tv_nsec) < std::tie(b.tv_sec, b.tv_nsec);
    }
  };
  std::multimap<struct timespec, T, tscomp> d_work;
  void gettime(struct timespec* ts);
  std::thread d_thread;
};

#include "delaypipe.cc"