Add random number generator support to the IO interface

src/io/v3/simulator.hpp

@@ -47,10 +47,15 @@ class SimulatorTransport {
     return simulator_handle_->template Send<M>(address, address_, request_id, message);
   }
 
-  std::time_t Now() { return std::time(nullptr); }
+  uint64_t Now() { return simulator_handle_->Now(); }
 
   bool ShouldShutDown() { return simulator_handle_->ShouldShutDown(); }
 
+  template <class D = std::poisson_distribution<>, class Return = uint64_t>
+  Return Rand(D distrib) {
+    return simulator_handle_->Rand<D, Return>(distrib);
+  }
+
  private:
   std::shared_ptr<SimulatorHandle> simulator_handle_;
   Address address_;
@@ -58,7 +63,7 @@ class SimulatorTransport {
 
 class Simulator {
  public:
-  void SetConfig(SimulatorConfig config) { simulator_handle_->SetConfig(config); }
+  Simulator(SimulatorConfig config) { simulator_handle_->SetConfig(config); }
 
   void ShutDown() { simulator_handle_->ShutDown(); }
 

src/io/v3/simulator_handle.hpp

@@ -227,6 +227,11 @@ class SimulatorHandle {
       return false;
     }
 
+    // clock ticks forwards by 400 microseconds on average
+    std::poisson_distribution<> time_distrib(400);
+    uint64_t clock_advance = time_distrib(rng_);
+    cluster_wide_time_microseconds_ += clock_advance;
+
     if (in_flight_.empty()) {
       return false;
     }
@@ -263,6 +268,7 @@ class SimulatorHandle {
 
   void SetConfig(SimulatorConfig config) {
     std::unique_lock<std::mutex> lock(mu_);
+    rng_ = std::mt19937{config.rng_seed};
     config_ = config;
     cv_.notify_all();
   }
@@ -340,6 +346,17 @@ class SimulatorHandle {
     in_flight_.emplace_back(std::make_pair(std::move(to_address), std::move(om)));
   }
 
+  uint64_t Now() {
+    std::unique_lock<std::mutex> lock(mu_);
+    return cluster_wide_time_microseconds_;
+  }
+
+  template <class D = std::poisson_distribution<>, class Return = uint64_t>
+  Return Rand(D distrib) {
+    std::unique_lock<std::mutex> lock(mu_);
+    return distrib(rng_);
+  }
+
  private:
   std::mutex mu_{};
   std::condition_variable cv_;
@@ -360,4 +377,5 @@ class SimulatorHandle {
   size_t servers_ = 0;
   std::set<Address> server_addresses_;
   SimulatorConfig config_;
+  std::mt19937 rng_{};
 };

src/io/v3/transport.hpp

@@ -14,6 +14,7 @@
 #pragma once
 
 #include <concepts>
+#include <random>
 #include <variant>
 
 #include "utils/result.hpp"
@@ -120,13 +121,21 @@ class Io {
     return implementation_.template Send<M>(address, request_id, message);
   }
 
-  /// The current system time. This time source should be preferred over
-  /// any other time source.
-  std::time_t Now() { return implementation_.Now(); }
+  /// The current system time in microseconds since the unix epoch.
+  /// This time source should be preferred over any other, because it
+  /// lets us deterministically control clocks from tests for making
+  /// things like timeouts deterministic.
+  uint64_t Now() { return implementation_.Now(); }
 
   /// Returns true of the system should shut-down.
   bool ShouldShutDown() { return implementation_.ShouldShutDown(); }
 
+  /// Returns a random number within the specified distribution.
+  template <class D = std::poisson_distribution<>, class Return = uint64_t>
+  Return Rand(D distrib) {
+    return implementation_.template Rand<D, Return>(distrib);
+  }
+
  private:
   I implementation_;
   Address address_;