Changelog

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All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[Unreleased]

[0.6.0] - 2026-09-13

Breaking changes: the minimum Elixir is now 1.19 with OTP 28, and VirtualClock.cancel_timer/2 returns the remaining virtual time, or false, where it previously returned :ok. Events scheduled for the same instant now fire in the order they were scheduled rather than the reverse. A virtual time that used to be silently truncated at the end of a long advance is no longer truncated, so a simulation can now report more messages than before.

Added

  • Property-based test suites (test/virtual_clock_property_test.exs, test/actor_simulation_property_test.exs) covering time additivity, event ordering, cancellation and simulation message counts
  • Mutation testing with muex in place of the broken muzak/exavier dependencies, which fail on current Elixir
  • doctest VirtualClock so the moduledoc and cancel_timer/2 examples are executed by the test suite

Changed

  • Minimum Elixir version is now 1.19, and minimum OTP 28, matching the versions CI verifies. (1.15 was the previous floor, needed by ex_doc ~> 0.40.)
  • CI matrix reduced to Elixir 1.19/1.20 with OTP 28/29, and the other five workflows aligned, which still pinned Elixir 1.15/1.18 and OTP 25/27
  • GitHub Actions updated to their current majors (checkout v7, cache v6, upload-artifact v7, download-artifact v8, setup-java v6, setup-go v7, the Pages actions, action-junit-report v6, action-gh-release v3 and setup-rust-toolchain v2), which also clears the Node 20 deprecation notices
  • Updated all dependencies, including ex_doc 0.38 → 0.40, credo 1.7.13 → 1.7.19, dialyxir 1.4.6 → 1.4.8, castore 1.0.15 → 1.0.21
  • Consolidated four duplicated message-dispatch blocks in ActorSimulation.Actor into shared helpers, and nine duplicated acknowledgement clauses in VirtualTimeGenStateMachine.Wrapper into shared delivery handling
  • FOSSA no longer scans generated/ or examples/: they are build output whose transitive dependencies (for example io.vlingo.xoom:xoom-actors, MPL-2.0) are not part of what is published
  • README and documentation index restructured to lead with install and runnable examples
  • Replaced length(x) > 0 with x != [] throughout, which is what Credo's expensive-empty-enum check asks for. Every expression was verified to hold a list, and the two where it may be nil use not in [nil, []] to keep the original short-circuit behaviour. Credo now reports no issues, down from 42

Fixed

  • Clock deliveries to VirtualTimeGenServer actors now carry a token and are acknowledged by that token alone. Actors previously acknowledged every message they handled, so an unrelated message could satisfy the wait for a delivered event and let the clock advance while the event was still queued - which made simulations intermittently under-count their messages
  • VirtualTimeGenStateMachine actors use the same token protocol, so a :gen_statem actor can no longer be advanced past an event it has not processed
  • ActorSimulation.run/2 now reads actor statistics until they settle. A single pass could sample a downstream actor before an upstream one had forwarded to it, so a finished simulation could report zero messages for the last actor in a chain
  • Events due at the same virtual instant now fire in scheduling order, matching real timers (previously reverse order)
  • VirtualClock.scheduled_count/1 now counts every scheduled event; it previously reported one per due time, undercounting events that shared a timestamp
  • VirtualClock.cancel_timer/2 now returns the remaining virtual milliseconds (or false), matching the TimeBackend behaviour and Process.cancel_timer/1
  • The acknowledgement watchdog is now tracked in the clock state, so a stale timeout can no longer fire against a later wait
  • Removed dead code: redundant Enum.each clauses in ActorSimulation.Actor, an unreachable pattern_to_interval/2 clause in the OMNeT++ generator, and unused VirtualScheduler accessors that had no server-side handlers

Test Reliability

  • Removed all Process.sleep/1-based synchronisation from the test suite: tests now wait on the observable effect (WaitUntil.wait_until/2) before advancing the clock, instead of guessing how long another process needs. The four remaining sleeps are deliberate and documented: two gen_server timeouts, which cannot be polled because any message resets them, and two :slow tests that exist to show real time is slow
  • Replaced real-time deadline assertions with load-tolerant bounds, so a busy machine slows the tests down rather than failing them
  • Fixed tests that claimed to use virtual time but did not: they scheduled timers from the test process, which uses that process's backend - real time by default - so the clock advance did nothing and the assertions were vacuous. They now schedule from inside the server, which is the documented pattern, and assert the resulting state
  • Gave assertions to tests that had none (they slept and then stopped the server): cancellation, per-instance clocks, send_after_self/2 and the "virtual time is faster than real time" claim now check what they claim
  • The dining philosophers diagram test no longer asserts that every philosopher eats: concurrent actors have no deterministic ordering, so that outcome is a race. It asserts the behaviour the scenario guarantees instead

Demos and Documentation

  • The century demo runs this repository's code instead of the published Hex package (Mix.install used to fetch ~> 0.5.0), so a fix made here can show up in it, and its workflow can catch a regression here. Its header no longer claims "milliseconds" where runs measure seconds
  • The century demo reports its goal honestly: it states how many of the 36,525 midnights triggered a backup and how many were skipped because the previous backup was still running, and checks that the two add up - which they do. The earlier (expected: 36525) line implied the simulation was losing work; the gap was the demo's own "ignore a trigger while already backing up" rule
  • README states the primary goal up front - the RxJS TestScheduler idea applied to the BEAM - alongside the simulation DSL and the generators, rather than leaving it at the bottom under "Inspiration"

[0.5.0] - 2025-10-27

Added

  • VirtualTimeGenStateMachine with full :gen_statem support
  • start_link/3, start/3, call/3, cast/2, stop/3 functions for VirtualTimeGenStateMachine
  • Compilation warnings for global virtual clock operations to prevent race conditions

Changed

  • Optimized VirtualClock event scheduling by using asynchronous operations
  • Time backend is now internal and transparent to client code
  • VirtualTimeGenServer and VirtualTimeGenStateMachine functions now emit warnings when using global clock injection
  • Removed complex wrapper module causing callback conflicts
  • Now uses native Erlang :gen_statem directly

Fixed

  • State enter callbacks now work correctly in VirtualTimeGenStateMachine
  • Long-running simulations timeout issues resolved
  • Both :handle_event_function and :state_functions callback modes supported

[0.4.0] - 2025-10-15

Added

  • Ractor (Rust) code generator with Ractor framework
  • Single-file generator examples for Ractor and VLINGO
  • Documentation for Ractor generator

Fixed

  • Separated generated interface code from customizable implementation code across all generators
  • Fixed Mermaid flowchart reports missing edges for dynamic sends

[0.3.0] - 2025-10-14

Added

  • Virtual delays feature for actors
  • Quiescence termination mode
  • Enhanced diagram generation with trace-based approach
  • Dining philosophers example

Changed

  • Refactored sleep handling into TimeBackend behaviour
  • Enhanced diagram generation

Fixed

  • Corrected termination labels in reports
  • Fixed diagram accuracy issues

[0.2.3] - 2025-10-14

Added

  • Generator documentation in README

Changed

  • Added console output in all generated code
  • Implemented thread-safe ConsoleLogger for Pony generator
  • Updated all example projects

[0.2.0] - 2025-10-12

Added

  • Code generators for CAF (C++), Pony, Phony (Go), and VLINGO (Java)
  • Mermaid report generator module
  • Full GenServer callback support including handle_continue/2 and call timeout handling
  • Termination conditions for simulations based on actor state
  • Enhanced Mermaid diagrams with sequence diagram features
  • Dining philosophers example
  • Single-file generator examples
  • Generator documentation

Changed

  • Reorganized documentation with quick start examples first
  • Enhanced GitHub Actions workflows
  • Updated license to include full MIT license text

Fixed

  • Dialyzer warnings
  • Flaky tests
  • Generator output issues

0.1.0 - 2025-10-11

Added

  • Initial release
  • VirtualTimeGenServer with virtual time support
  • VirtualClock for event scheduling
  • Switchable real/virtual time backends
  • Actor Simulation DSL
  • Message patterns (periodic, rate-based, burst)
  • Process-in-the-Loop support
  • Pattern matching responses with on_match
  • Message tracing and Mermaid diagram generation

[Unreleased]: https://github.com/d-led/gen_server_virtual_time/compare/v0.2.0...HEAD [0.2.4]: https://github.com/d-led/gen_server_virtual_time/compare/v0.2.3...v0.2.4 [0.2.0]: https://github.com/d-led/gen_server_virtual_time/compare/v0.1.0...v0.2.0