Add some instrumentation to keep track of dispatcher cost

Dependencies

• [2] RKW3XA4U Fix potential race in dispatcher wakeup
• [3] 4I2HF4L3 Unindent
• [*] MHVIT4JY Split hydra-queue-runner.cc more
• [*] 24BMQDZA Start of single-process hydra-queue-runner
• [*] PLOZBRTR Add command ‘hydra-queue-runner --status’ to show current status
• [*] HJOEIMLR Refactor

Change contents

• edit in src/hydra-queue-runner/builder.cc at line 12
  [5.350]

  [5.350]
  +

  + nrStepsStarted++;
• edit in src/hydra-queue-runner/dispatcher.cc at line 35
  [5.15208]

  [5.15208]
  + nrDispatcherWakeups++;

  +

  + auto now1 = std::chrono::steady_clock::now();
• edit in src/hydra-queue-runner/dispatcher.cc at line 40
  [3.40]

  [5.15255]
  +

  + auto now2 = std::chrono::steady_clock::now();

  +

  + dispatchTimeMs += std::chrono::duration_cast<std::chrono::milliseconds>(now2 - now1).count();
• edit in src/hydra-queue-runner/dispatcher.cc at line 54
  [2.394]→[3.493:528](∅→∅),[3.493]→[3.493:528](∅→∅)
  − nrDispatcherWakeups++;
• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 553
  [7.1319]

  [7.1319]
  + root.attr("nrStepsStarted", nrStepsStarted);
• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 565
  [7.1574]

  [7.1574]
  + root.attr("dispatchTimeMs", dispatchTimeMs);

  + root.attr("dispatchTimeAvgMs", nrDispatcherWakeups == 0 ? 0.0 : (float) dispatchTimeMs / nrDispatcherWakeups);
• edit in src/hydra-queue-runner/state.hh at line 298
  [8.5602]

  [8.5602]
  + counter nrStepsStarted{0};
• edit in src/hydra-queue-runner/state.hh at line 311
  [8.6028]

  [8.6028]
  + counter dispatchTimeMs{0};