CE Club Seminar - Designing a Programming Language Shared-Memory Concurrency Semantics

#Concurrency #semantics #programming #language #sequential #consistency

A concurrency semantics (aka a memory model) for a programming language defines the allowed behaviors of multithreaded programs. For programmers, sequential consistency (i.e., standard interleaving-based semantics) is considered as the most intuitive model. However, it is too costly to implement. Designing a satisfactory substitute is highly challenging as it requires to carefully balance the conflicting desires of programmers, compilers, and hardware. In this talk I will introduce this challenge and the key ideas behind the prototype example of the C/C++ concurrency model from 2011. Then, I will demonstrate the drawback of the C/C++ approach, notoriously known as the “out-of-thin-air” problem. I will conclude by describing the “promising semantics” solution, and remaining challenges.

We study basic demand-aware problems in offchain network design: Efficiently mapping users to an offchain topology of a known structure as well as constructing a topology of a bounded number of channels that can serve well typical payments. Likewise, we suggest an approach for jointly serving multiple payments by finding an equivalent set of payments that has the same impact on user balance but can be served efficiently in a given topology.