siathalysedi / porcupine

A fast linearizability checker written in Go 🔎

Porcupine

Porcupine is a fast linearizability checker for testing the correctness of distributed systems. It takes a sequential specification as executable Go code, along with a concurrent history, and it determines whether the history is linearizable with respect to the sequential specification.

Porcupine implements the algorithm described in Faster linearizability checking via P-compositionality, an optimization of the algorithm described in Testing for Linearizability.

Porcupine is faster and can handle more histories than Knossos's linearizability checker. Testing on the data in test_data/jepsen/, Porcupine is generally 1,000x-10,000x faster and has a much smaller memory footprint. On histories where it can take advantage of P-compositionality, Porcupine can be millions of times faster.

Usage

Porcupine takes an executable model of a system along with a history, and it runs a decision procedure to determine if the history is linearizable with respect to the model. Porcupine supports specifying history in two ways, either as a list of operations with given call and return times, or as a list of call/return events in time order.

See model.go for documentation on how to write a model or specify histories. Once you've written a model and have a history, you can use the CheckOperations and CheckEvents functions to determine if your history is linearizable.

Example

Suppose we're testing linearizability for operations on a read/write register that's initialized to 0. We write a sequential specification for the register like this:

type registerInput struct {
    op bool // false = write, true = read
    value int
}

// a sequential specification of a register
registerModel := porcupine.Model{
    Init: func() interface{} {
        return 0
    },
    // step function: takes a state, input, and output, and returns whether it
    // was a legal operation, along with a new state
    Step: func(state, input, output interface{}) (bool, interface{}) {
        regInput := input.(registerInput)
        if regInput.op == false {
            return true, regInput.value // always ok to execute a write
        } else {
            readCorrectValue := output == state
            return readCorrectValue, state // state is unchanged
        }
    },
}

Suppose we have the following concurrent history from a set of 3 clients. In a row, the first | is when the operation was invoked, and the second | is when the operation returned.

C0:  |-------- Write(100) --------|
C1:      |--- Read(): 100 ---|
C2:          |- Read(): 0 -|

We encode this history as follows:

events := []porcupine.Event{
    // C0: Write(100)
    {Kind: porcupine.CallEvent, Value: registerInput{false, 100}, Id: 0},
    // C1: Read()
    {Kind: porcupine.CallEvent, Value: registerInput{true, 0}, Id: 1},
    // C2: Read()
    {Kind: porcupine.CallEvent, Value: registerInput{true, 0}, Id: 2},
    // C2: Completed Read -> 0
    {Kind: porcupine.ReturnEvent, Value: 0, Id: 2},
    // C1: Completed Read -> 100
    {Kind: porcupine.ReturnEvent, Value: 100, Id: 1},
    // C0: Completed Write
    {Kind: porcupine.ReturnEvent, Value: 0, Id: 0},
}

We can have Porcupine check the linearizability of the history as follows:

ok := porcupine.CheckEvents(registerModel, events)
// returns true

Now, suppose we have another history:

C0:  |------------- Write(200) -------------|
C1:    |- Read(): 200 -|
C2:                        |- Read(): 0 -|

We can check the history with Porcupine and see that it's not linearizable:

ok := porcupine.CheckEvents(registerModel, events)
// returns false

See porcupine_test.go for more examples on how to write models and histories.

Notes

Porcupine's API is not stable yet. Please vendor this package before using it.

Citation

If you use Porcupine in any way in academic work, please cite the following:

@misc{athalye2017porcupine,
  author = {Anish Athalye},
  title = {Porcupine: A fast linearizability checker in {Go}},
  year = {2017},
  howpublished = {\url{https://github.com/anishathalye/porcupine}},
  note = {commit xxxxxxx}
}

License

Copyright (c) 2017-2018 Anish Athalye. Released under the MIT License. See LICENSE.md for details.