IOSim is a simulator monad that supports:
- asynchronous exceptions
- simulated time
- timeout API
- software transaction memory (STM)
- concurrency: both low-level
forkIOas well asasyncstyle - strict STM
- access to lazy ST
- schedule discovery (see IOSimPOR)
- event log
- dynamic tracing
- tracing committed changes to
TVar,TMVars, etc. - labeling of threads,
TVar's, etc.
io-classes provides an interface, which allows writing code that can be run
in both real IO and IOSim. It is a drop-in replacement for IO, and
supports interfaces commonly known from base, exceptions, stm, async,
or time packages.
One of the principles of io-classes was to stay as close to IO as possible,
thus most of the IO instances are directly referring to base or async
API. However, we made some distinctions, which are reported below.
io-classes supports a novel hierarchy for error-handling monads as well as
more familiar exception style. The new hierarchy provides bracket and
finally functions in the MonadThrow class, while catch style operators
are provided by a super-class MonadCatch. Both bracket and finally are
the most common functions used to write code with robust exception handling,
exposing them through the more basic MonadThrow class informs the reader
/ reviewer that no tricky error handling is done in that section of the code
base.
IOSim exposes a detailed trace, which can be enhanced by labeling threads, or
mutable variables, tracing Dynamic values (which can be recovered from the
trace), or simple String based tracing. Although it's agnostic concerning
the logging framework, it worked for us particularly well using
contra-tracer. It has been used to develop, test, and debug
a complex, highly concurrent, distributed system
(ouroboros-network), in particular
- write network simulations, to verify a complex networking stack;
- write disk IO simulations, to verify a database implementation.
io-sim: provides two simulator interpreters:IOSimandIOSimPOR- an enhancedIOSimversion with schedule discovery capabilities.io-classes: class bases interface, which allows to to abstract over the monad- [
strict-stm]: strict STM operations - [
si-timers]: non-standard timers API
New issues should be reported in this repository.