arXiv subjects

Konstantinos Kallas

Publications and source records attributed to Konstantinos Kallas.

11 recordsLinked to original sources

arXiv2026

PopPy: Opportunistically Exploiting Parallelism in Python Agentic Workflows

Agentic workflows, which compose calls to ML models using a general-purpose programming language like Python, are widely used for a variety of user-facing tasks, from software engineering to enterprise automation, making their end-to-end latency a critical bottleneck. To improve their latency, developers can either manually parallelize them or use restricted agentic frameworks that cannot express or exploit all forms of parallelization. We address this by developing PopPy, a system that parallelizes external calls, e.g., AI models, in agentic workflows written in a very expressive subset of Python. PopPy combines an ahead-of-time compiler with a runtime, addressing three key challenges in extracting parallelism from Python applications: language complexity, dynamic dispatch, and variable mutation. On a set of real-world agentic workflows, PopPy achieves up to $6.7\times$ speedups in end-to-end execution time, compared to standard Python execution and several agentic frameworks, while preserving the sequential program semantics.

cs.DC↗

arXiv2026

An AI Agent Execution Environment to Safeguard User Data

AI agents promise to serve as general-purpose personal assistants for their users, which requires them to have access to private user data (e.g., personal and financial information). This poses a serious risk to security and privacy: an AI model may hallucinate or make mistakes, and adversaries may attack it (e.g., via prompt injection) to exfiltrate user data. This paper presents GAAP (Guaranteed Accounting for Agent Privacy), an execution environment for AI agents that guarantees confidentiality for private user data. Crucially, GAAP provides this guarantee deterministically, without trusting the agent with private user data, and without requiring any AI model or the user prompt to be free of attacks. Through dynamic and directed user prompts, GAAP collects permission specifications from users describing how their private data may be shared. GAAP then enforces that the agent's data disclosures comply with these specifications by tracking how the AI agent accesses and uses private user data. GAAP augments Information Flow Control with novel persistent data stores and annotations that enable tracking the private information flow both across steps of a single task and over multiple separate tasks. Our evaluation confirms that GAAP blocks all data disclosure attacks, including those that make other state-of-the-art systems disclose private user data to untrusted parties, with only a small impact on agent utility.

cs.CR↗

arXiv2026

Opportunistically Parallel Lambda Calculus

Scripting languages are widely used to compose external calls such as native libraries and network services. In such scripts, execution time is often dominated by waiting for these external calls, rendering traditional single-language optimizations ineffective. To address this, we propose a novel opportunistic evaluation strategy for scripting languages based on a core lambda calculus that automatically dispatches independent external calls in parallel and streams their results. We prove that our approach is confluent, ensuring that it preserves the programmer's original intent, and that it eventually executes every external call. We implement this approach in a scripting language called Opal. We demonstrate the versatility and performance of Opal, focusing on programs that invoke heavy external computation through the use of large language models (LLMs) and other APIs. Across five scripts, we compare to several state-of-the-art baselines and show that opportunistic evaluation improves total running time (up to $6.2\times$) and latency (up to $12.7\times$) compared to standard sequential Python, while performing very close (between $1.3\%$ and $18.5\%$ running time overhead) to hand-tuned manually optimized asynchronous Rust. For Tree-of-Thoughts, a prominent LLM reasoning approach, we achieve a $6.2\times$ performance improvement over the authors' own implementation.

cs.PL↗

arXiv2025

Caruca: Effective and Efficient Specification Mining for Opaque Software Components

A wealth of state-of-the-art systems demonstrate impressive improvements in performance, security, and reliability on programs composed of opaque components, such as Unix shell commands. To reason about commands, these systems require partial specifications. However, creating such specifications is a manual, laborious, and error-prone process, limiting the practicality of these systems. This paper presents Caruca, a system for automatic specification mining for opaque commands. To overcome the challenge of language diversity across commands, Caruca first instruments a large language model to translate a command's user-facing documentation into a structured invocation syntax. Using this representation, Caruca explores the space of syntactically valid command invocations and execution environments. Caruca concretely executes each command-environment pair, interposing at the system-call and filesystem level to extract key command properties such as parallelizability and filesystem pre- and post-conditions. These properties can be exported in multiple specification formats and are immediately usable by existing systems. Applying Caruca across 60 GNU Coreutils, POSIX, and third-party commands across several specification-dependent systems shows that Caruca generates correct specifications for all but one case, completely eliminating manual effort from the process and currently powering the full specifications for a state-of-the-art static analysis tool.

cs.SE↗

arXiv2025

NaSh: Guardrails for an LLM-Powered Natural Language Shell

We explore how a shell that uses an LLM to accept natural language input might be designed differently from the shells of today. As LLMs may produce unintended or unexplainable outputs, we argue that a natural language shell should provide guardrails that empower users to recover from such errors. We concretize some ideas for doing so by designing a new shell called NaSh, identify remaining open problems in this space, and discuss research directions to address them.

cs.OS↗

arXiv2022

Stream Processing With Dependency-Guided Synchronization (Extended Version)

Real-time data processing applications with low latency requirements have led to the increasing popularity of stream processing systems. While such systems offer convenient APIs that can be used to achieve data parallelism automatically, they offer limited support for computations that require synchronization between parallel nodes. In this paper, we propose *dependency-guided synchronization (DGS)*, an alternative programming model for stateful streaming computations with complex synchronization requirements. In the proposed model, the input is viewed as partially ordered, and the program consists of a set of parallelization constructs which are applied to decompose the partial order and process events independently. Our programming model maps to an execution model called *synchronization plans* which supports synchronization between parallel nodes. Our evaluation shows that APIs offered by two widely used systems -- Flink and Timely Dataflow -- cannot suitably expose parallelism in some representative applications. In contrast, DGS enables implementations with scalable performance, the resulting synchronization plans offer throughput improvements when implemented manually in existing systems, and the programming overhead is small compared to writing sequential code.

cs.PL↗

arXiv2021

Report on the "The Future of the Shell" Panel at HotOS 2021

This document summarizes the challenges and possible research directions around the shell and its ecosystem, collected during and after the HotOS21 Panel on the future of the shell. The goal is to create a snapshot of what a number of researchers from various disciplines -- connected to the shell to varying degrees -- think about its future. We hope that this document will serve as a reference for future research on the shell and its ecosystem.

cs.OS↗

arXiv2021

An Order-Aware Dataflow Model for Parallel Unix Pipelines

We present a dataflow model for modelling parallel Unix shell pipelines. To accurately capture the semantics of complex Unix pipelines, the dataflow model is order-aware, i.e., the order in which a node in the dataflow graph consumes inputs from different edges plays a central role in the semantics of the computation and therefore in the resulting parallelization. We use this model to capture the semantics of transformations that exploit data parallelism available in Unix shell computations and prove their correctness. We additionally formalize the translations from the Unix shell to the dataflow model and from the dataflow model back to a parallel shell script. We implement our model and transformations as the compiler and optimization passes of a system parallelizing shell pipelines, and use it to evaluate the speedup achieved on 47 pipelines.

cs.PL↗

arXiv2021

PaSh: Light-touch Data-Parallel Shell Processing

This paper presents {\scshape PaSh}, a system for parallelizing POSIX shell scripts. Given a script, {\scshape PaSh} converts it to a dataflow graph, performs a series of semantics-preserving program transformations that expose parallelism, and then converts the dataflow graph back into a script -- one that adds POSIX constructs to explicitly guide parallelism coupled with {\scshape PaSh}-provided {\scshape Unix}-aware runtime primitives for addressing performance- and correctness-related issues. A lightweight annotation language allows command developers to express key parallelizability properties about their commands. An accompanying parallelizability study of POSIX and GNU commands -- two large and commonly used groups -- guides the annotation language and optimized aggregator library that {\scshape PaSh} uses. Finally, {\scshape PaSh}'s {\scshape PaSh}'s extensive evaluation over 44 unmodified {\scshape Unix} scripts shows significant speedups ($0.89$--$61.1\times$, avg: $6.7\times$) stemming from the combination of its program transformations and runtime primitives.

cs.DC↗

arXiv2021

Serverless Workflows with Durable Functions and Netherite

Serverless is an increasingly popular choice for service architects because it can provide elasticity and load-based billing with minimal developer effort. A common and important use case is to compose serverless functions and cloud storage into reliable workflows. However, existing solutions for authoring workflows provide a rudimentary experience compared to writing standard code in a modern programming language. Furthermore, executing workflows reliably in an elastic serverless environment poses significant performance challenges. To address these, we propose Durable Functions, a programming model for serverless workflows, and Netherite, a distributed execution engine to execute them efficiently. Workflows in Durable Functions are expressed as task-parallel code in a host language of choice. Internally, the workflows are translated to fine-grained stateful communicating processes, which are load-balanced over an elastic cluster. The main challenge is to minimize the cost of reliably persisting progress to storage while supporting elastic scale. Netherite solves this by introducing partitioning, recovery logs, asynchronous snapshots, and speculative communication. Our results show that Durable Functions simplifies the expression of complex workflows, and that Netherite achieves lower latency and higher throughput than the prevailing approaches for serverless workflows in Azure and AWS, by orders of magnitude in some cases.

cs.DC↗

arXiv2021

Mir: Automated Quantifiable Privilege Reduction Against Dynamic Library Compromise in JavaScript

Third-party libraries ease the development of large-scale software systems. However, they often execute with significantly more privilege than needed to complete their task. This additional privilege is often exploited at runtime via dynamic compromise, even when these libraries are not actively malicious. Mir addresses this problem by introducing a fine-grained read-write-execute (RWX) permission model at the boundaries of libraries. Every field of an imported library is governed by a set of permissions, which developers can express when importing libraries. To enforce these permissions during program execution, Mir transforms libraries and their context to add runtime checks. As permissions can overwhelm developers, Mir's permission inference generates default permissions by analyzing how libraries are used by their consumers. Applied to 50 popular libraries, Mir's prototype for JavaScript demonstrates that the RWX permission model combines simplicity with power: it is simple enough to automatically infer 99.33% of required permissions, it is expressive enough to defend against 16 real threats, it is efficient enough to be usable in practice (1.93% overhead), and it enables a novel quantification of privilege reduction.

cs.CR↗