grpc/test/cpp/qps/interarrival.h

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#ifndef TEST_QPS_TIMER_H
#define TEST_QPS_TIMER_H

#include <chrono>
#include <cmath>
#include <random>

#include <grpc++/config.h>

namespace grpc {
namespace testing {

// First create classes that define a random distribution
// Note that this code does not include C++-specific random distribution
// features supported in std::random. Although this would make this code easier,
// this code is required to serve as the template code for other language
// stacks. Thus, this code only uses a uniform distribution of doubles [0,1)
// and then provides the distribution functions itself.
  
class RandomDist {
 public:
  RandomDist() {}
  virtual ~RandomDist() = 0;
  // Argument to operator() is a uniform double in the range [0,1)
  virtual double operator() (double uni) const = 0;
};

inline RandomDist::~RandomDist() {}
 
class UniformDist GRPC_FINAL: public RandomDist {
public:
 UniformDist(double lo, double hi): lo_(lo), range_(hi-lo) {}
 ~UniformDist() GRPC_OVERRIDE {}
 double operator() (double uni) const GRPC_OVERRIDE {return uni*range_+lo_;}
private:
  double lo_;
  double range_;
};

class ExpDist GRPC_FINAL : public RandomDist {
public:
 explicit ExpDist(double lambda): lambda_recip_(1.0/lambda) {}
 ~ExpDist() GRPC_OVERRIDE {}
 double operator() (double uni) const GRPC_OVERRIDE {
   // Note: Use 1.0-uni above to avoid NaN if uni is 0
   return lambda_recip_ * (-log(1.0-uni));
 }
private:
  double lambda_recip_;
};
 
class DetDist GRPC_FINAL : public RandomDist {
public:
 explicit DetDist(double val): val_(val) {}
 ~DetDist() GRPC_OVERRIDE {}
 double operator() (double uni) const GRPC_OVERRIDE {return val_;}
private:
  double val_;
};

class ParetoDist GRPC_FINAL : public RandomDist {
public:
  ParetoDist(double base, double alpha): base_(base), alpha_recip_(1.0/alpha) {}
  ~ParetoDist() GRPC_OVERRIDE {}
  double operator() (double uni) const GRPC_OVERRIDE {
   // Note: Use 1.0-uni above to avoid div by zero if uni is 0
    return base_ / pow(1.0-uni, alpha_recip_);
 }
private:
 double base_;
 double alpha_recip_;
};
 
// A class library for generating pseudo-random interarrival times
// in an efficient re-entrant way. The random table is built at construction
// time, and each call must include the thread id of the invoker

using qps_random_engine = std::default_random_engine;
 
class InterarrivalTimer {
public:
  InterarrivalTimer(const RandomDist& r, int threads, int entries=1000000) {
    qps_random_engine gen;
    std::uniform_real_distribution<double> uniform(0.0,1.0);
    for (int i=0; i<entries; i++) {
      random_table_.push_back(std::chrono::microseconds(static_cast<int64_t>(1000000.0*r(uniform(gen)))));
    }
    // Now set up the thread positions
    for (int i=0; i<threads; i++) {
      thread_posns_.push_back(random_table_.begin() + (entries * i)/threads);
    }
  }
  virtual ~InterarrivalTimer() {};
  
  std::chrono::microseconds operator() (int thread_num) {
    auto ret = *(thread_posns_[thread_num]++);
    if (thread_posns_[thread_num] == random_table_.end())
      thread_posns_[thread_num] = random_table_.begin();
    return ret;
  }
 private:
  typedef std::vector<std::chrono::microseconds> time_table;
  std::vector<time_table::const_iterator> thread_posns_;
  time_table random_table_;
};

}
}

#endif