concuerror.com

What It Is

Concuerror is a stateless model-checking tool for Erlang programs. Its primary purpose is to debug, test, and verify concurrent programs, with a focus on typical concurrency issues such as deadlocks and errors caused by race conditions. Unlike tests that rely on random scheduling, Concuerror systematically explores schedules with “meaningful differences,” so it can not only find bugs but also, once exploration is complete, verify the absence of certain classes of concurrency errors.

Core Capabilities and Ecosystem

The tool controls process scheduling during Erlang tests so that only one process runs at a time, and records operations that may be affected by scheduling, such as receive, message sending and delivery, registry operations, and ETS. It then analyzes pairs of operations in the trace that actually race, and generates new interleavings by reversing their execution order. This mechanism is based on stateless model checking and dynamic partial order reduction; the FAQ also mentions the use of Optimal Dynamic Partial Order Reduction to reduce schedule explosion.

For integration, Concuerror automatically instruments and reloads the modules used by a test, relies on the Erlang code path, and supports common input-file options. It provides command-line options such as --show_races, --interleaving_bound, --graph, --print_depth, and --after-timeout; --graph requires the dot tool to generate images. The website also offers basic tutorials, an FAQ, Hexdocs API documentation, papers, Github Issues, a mailing list, and a changelog. The documentation sits at the intersection of engineering and research, with fairly in-depth explanations.

Pricing and Open Source

The captured text does not provide pricing information, nor does it clearly state a license. The page provides a Github entry point and a way to report issues, but the body text alone is not enough to determine its open-source status or business model. It appears more like a local development/testing tool than a hosted SaaS product.

Pros and Cons

Its strengths are that it closely matches the Erlang/OTP concurrency model, can reproduce rare scheduling issues that random testing struggles to trigger, and has verification capabilities. Its downsides are that the scheduling space for complex concurrent programs can be enormous, and even with partial-order reduction it may still run for a long time; random testing mode has not yet been implemented; and support for some built-in operations may be incomplete. It has special handling for timeouts, time functions, and nondeterministic functions. NIF modules cannot be intercepted, instrumented, or race-analyzed, and are very likely to cause crashes.

Who It’s For and Access from China

Concuerror is suitable for Erlang/OTP backend teams, communications systems, distributed systems, and teams with high requirements for concurrency correctness. It is also useful for researchers validating concurrent algorithms. The source text does not provide information about access from China, so this is unknown; there is also no information about payment methods. If it cannot be used, Erlang’s built-in testing ecosystem or other concurrency/model-checking tools may be considered as alternatives, but the specific choice should depend on the technical stack.