Compute Express Link (CXL) offers byte-addressable, cache-coherent remote memory accesses across multiple hosts. Unfortunately, the CXL specification lacks mechanisms to ensure safe interoperability between heterogeneous host architectures with diverse cache coherence (CC) protocols and memory consistency models (MCMs). This semantic gap poses fundamental challenges and a significant barrier to adopting CXL in modern heterogeneous data centers.

We introduce$\mathbf{C}^{\mathbf{3}}$, a systematic methodology for designing Compute Express Link (CXL) coherence controllers, to overcome interoperability challenges that arise from the mismatch of coherence protocols and memory consistency models in heterogeneous CXL-connected systems. Crucially, CXL lacks a unified heterogeneous computing interface, which can lead to unpredictable and inconsistent behavior when multiple heterogeneous devices decide to share cache-coherent CXL memory. C$^{3}$acts as a pivotal interface between diverse heterogeneous compute units, bridging the semantic differences without necessitating disruptive changes to existing system architectures. Our approach hinges on two key principles: delegating memory operations across coherence domains and enforcing atomicity at domain boundaries, thereby preserving the native memory consistency model semantics of each unit. We implement$\mathbf{C}^{\mathbf{3}}$as a generic gem5 model and validate its correctness through exhaustive litmus testing. We also show that$\mathbf{C}^{\mathbf{3}}$incurs minimal performance overhead compared to unified native coherence protocols.

This paper presents J-NVM, a framework to access efficiently Non-Volatile Main Memory (NVMM) in Java. J-NVM offers a fully-fledged interface to persist plain Java objects using failure-atomic blocks. This interface relies internally on proxy objects that intermediate direct off-heap access to NVMM. The framework also provides a library of highly-optimized persistent data types that resist reboots and power failures. We evaluate J-NVM by implementing a persistent backend for the Infinispan data store. Our experimental results, obtained with a TPC-B like benchmark and YCSB, show that J-NVM is consistently faster than other approaches at accessing NVMM in Java.

Atomic multicast is a communication primitive that delivers messages to multiple groups of processes according to some total order, with each group receiving the projection of the total order onto messages addressed to it. To be scalable, atomic multicast needs to be genuine, meaning that only the destination processes of a message should participate in ordering it. In this paper we propose a novel genuine atomic multicast protocol that in the absence of failures takes as low as 3 message delays to deliver a message when no other messages are multicast concurrently to its destination groups, and 5 message delays in the presence of concurrency. This improves the latencies of both the fault-tolerant version of classical Skeen's multicast protocol (6 or 12 message delays, depending on concurrency) and its recent improvement by Coelho et al. (4 or 8 message delays). To achieve such low latencies, we depart from the typical way of guaranteeing fault-tolerance by replicating each group with Paxos. Instead, we weave Paxos and Skeen's protocol together into a single coherent protocol, exploiting opportunities for white-box optimisations. We experimentally demonstrate that the superior theoretical characteristics of our protocol are reflected in practical performance pay-offs.