README.md



ACTRIS COQ DEVELOPMENT
This directory contains the artifact for the paper "Actris: Session Type
Based Reasoning in Separation Logic".
It has been built and tested with the following dependencies

Coq 8.9.1

std++ at
commit f9830af6.

iris at
commit 0c4e2984.

In order to build, install the above dependencies and then run
make -j [num CPU cores] to compile Actris.

Directory structure

Theory
The theory can be found in theories/channel. Some used utilities can be found
in theories/utils.
The files correspond to the following:


theories/channel/channel.v: The definitional semantics of bidirectional
channels in HeapLang.

theories/channel/proto_model.v: The CPS model of dependent separation
protocols.

theories/channel/proto_channel.v: The definition of the connective ↣ for
channel ownership and the proof rules of the Actris logic.

theories/channel/proofmode.v: The Coq tactics for symbolic execution.


Examples
The examples can be found in theories/examples.
The following list gives a mapping between the examples in the paper and their
mechanization in Coq:


Introduction: theories/examples/basics.v


Tour of Actris


2.3 Basic, sort: theories/examples/sort.v

2.4 Higher-Order Functions, sort_func: theories/examples/sort.v

2.5 Branching: theories/examples/sort_br_del.v

2.6 Recursion: theories/examples/sort_br_del.v

2.7 Delegation: theories/examples/sort_br_del.v

2.8 Dependent: theories/examples/sort_fg.v


Manifest sharing via locks


3.1 Sample program: theories/examples/basics.v

3.2 Distributed mapper: theories/examples/map.v


Case study: map reduce:


Utilities for shuffling/grouping: theories/utils/group.v

Implementation and verification: theories/examples/map_reduce.v


Differences between the formalization and the paper
There are a number of small differences between the paper presentation
of Actris and the formalization in Coq, that are briefly discussed here.

Connectives for physical ownership of channels
In the paper physical ownership of a channel is formalized using a single
connective (c1,c2) ↣ (vs1,vs2), while the mechanisation has two connectives
for the endpoints and one for connecting them, namely:


chan_own γ Left vs1 and chan_own γ Right vs1

is_chan N γ c1 c2

Where γ is a ghost name and N the invariant used internally. This setup is
less intuitive but gives rise to a more practical Jacobs/Piessens-style spec
of recv that does not need a closing view shift (to handle the case that
the buffer is empty).

Later modalities in primitive rules for channels
The primitive rules for send and recv (send_spec and recv_spec) contain
three later modalities, which are omitted for brevity's sake in the paper. These
later modalities expose that these operations perform at least three steps in
the operational semantics, and are needed to deal with the three levels of
indirection in the invariant for protocols: 1.) the ▶ in the CPS encoding of
protocols, 2.) the higher-order ghost state used for ownership of protocols,
3.) the opening of the protocol invariant.