Replay

Umpire provides a lightweight replay capability that can be used to investigate performance of particular allocation patterns and reproduce bugs.

Input Example

A log can be captured and stored as a JSON file, then used as input to the replay application (available under the bin directory). The replay program will read the replay log, and recreate the events that occured as part of the run that generated the log.

The file tut_replay.cpp makes a umpire::strategy::QuickPool:

  auto allocator = rm.getAllocator("HOST");
  auto pool =
      rm.makeAllocator<umpire::strategy::QuickPool>("pool", allocator);

This allocator is used to perform some randomly sized allocations, and later free them:

  std::generate(allocations.begin(), allocations.end(),
                [&]() { return pool.allocate(random_number()); });

  for (auto& ptr : allocations)
    pool.deallocate(ptr);

Running the Example

Running this program:

UMPIRE_REPLAY="On" ./bin/examples/tutorial/tut_replay > tut_replay_log.json

will write Umpire replay events to the file tut_replay_log.json. You can see that this file contains JSON formatted lines.

Replaying the session

Loading this file with the replay program will replay this sequence of umpire::Allocator creation, allocations, and deallocations:

./bin/replay -i ../tutorial/examples/tut_replay_log.json