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#ifndef TEST_QPS_INTERARRIVAL_H
#define TEST_QPS_INTERARRIVAL_H
#include <chrono>
#include <cmath>
#include <cstdlib>
#include <vector>
#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() {}
// ExpDist implements an exponential distribution, which is the
// interarrival distribution for a Poisson process. The parameter
// lambda is the mean rate of arrivals. This is the
// most useful distribution since it is actually additive and
// memoryless. It is a good representation of activity coming in from
// independent identical stationary sources. For more information,
// see http://en.wikipedia.org/wiki/Exponential_distribution
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_;
};
// UniformDist implements a random distribution that has
// interarrival time uniformly spread between [lo,hi). The
// mean interarrival time is (lo+hi)/2. For more information,
// see http://en.wikipedia.org/wiki/Uniform_distribution_%28continuous%29
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_;
};
// DetDist provides a random distribution with interarrival time
// of val. Note that this is not additive, so using this on multiple
// flows of control (threads within the same client or separate
// clients) will not preserve any deterministic interarrival gap across
// requests.
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_;
};
// ParetoDist provides a random distribution with interarrival time
// spread according to a Pareto (heavy-tailed) distribution. In this
// model, many interarrival times are close to the base, but a sufficient
// number will be high (up to infinity) as to disturb the mean. It is a
// good representation of the response times of data center jobs. See
// http://en.wikipedia.org/wiki/Pareto_distribution
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
class InterarrivalTimer {
public:
InterarrivalTimer() {}
void init(const RandomDist& r, int threads, int entries = 1000000) {
for (int i = 0; i < entries; i++) {
// rand is the only choice that is portable across POSIX and Windows
// and that supports new and old compilers
const double uniform_0_1 = rand() / RAND_MAX;
random_table_.push_back(
std::chrono::nanoseconds(static_cast<int64_t>(1e9 * r(uniform_0_1))));
}
// 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::nanoseconds 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::nanoseconds> time_table;
std::vector<time_table::const_iterator> thread_posns_;
time_table random_table_;
};
}
}
#endif