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HPActor: A Million-Level Concurrent Distributed Actor Framework for AI Inference

HPActor is a high-performance distributed framework based on the Actor model, designed specifically for building next-generation AI inference service platforms. It achieves million-level concurrency support through C++20 coroutines, lock-free schedulers, and a two-level Slab memory allocator, making it particularly suitable for long-running interactive agent workflows.

Actor模型分布式系统C++20协程AI推理LLM智能体高并发无锁编程内存管理
Published 2026-05-17 08:14Recent activity 2026-05-17 08:20Estimated read 8 min
HPActor: A Million-Level Concurrent Distributed Actor Framework for AI Inference
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Section 01

[Introduction] HPActor: A Million-Level Concurrent Distributed Actor Framework for AI Inference

HPActor is a high-performance distributed framework based on the Actor model, designed specifically for building next-generation AI inference service platforms. It achieves million-level concurrency support through C++20 coroutines, lock-free schedulers, and a two-level Slab memory allocator, making it particularly suitable for long-running interactive agent workflows.

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Section 02

Background and Motivation: Demand Shift in AI Inference Services

With the rapid development of Large Language Models (LLMs), the demand for AI inference services has undergone a fundamental shift. The traditional stateless request-response API model cannot meet the needs of long-running, stateful, multi-turn interactive agent workflows. HPActor emerged as a solution, based on the Actor model and implemented in C++20 to fully leverage modern hardware performance, with the goal of supporting million-level concurrent Actor scheduling and management.

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Section 03

Core Advantages of the Actor Model and Its Adaptation to AI Inference

The Actor model was proposed by Carl Hewitt in 1973, with core features including state encapsulation, message passing, concurrent execution, and fault tolerance isolation. For AI inference services, this model is suitable for modeling user sessions, model instances, and tool calls as separate Actors, enabling state retention, lock-free communication, and fault tolerance isolation.

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Section 04

Technical Architecture: Implementation of High Performance and Distribution

1. C++20 Coroutine-Driven Scheduling System

Uses stackless coroutines; the HybridScheduler hybrid scheduler combines work stealing, adaptive victim selection, multi-level priority queues, EDF scheduling, and hierarchical time wheels.

2. Two-Level Slab Memory Allocator

Tier0 uses an mmap-based SegmentProvider; Tier1 uses a per-thread independent SlabCache to avoid fragmentation and lock contention.

3. Lock-Free Message Passing

Based on MPSC lock-free queues, supporting backpressure control and dead-letter queues.

4. Distributed and Network Layer

Supports TCP/TLS, dynamic connection pools, and service discovery (UDP registration/Gossip protocol).

5. Supervision and Fault Tolerance

Erlang-style supervision tree, supporting OneForOne/AllForOne strategies and graceful shutdown mechanisms.

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Section 05

Special Optimizations for AI Inference: Sessions, Streaming, and Tool Orchestration

Stateful Inference Sessions

Models user sessions as long-lived Actors, retaining conversation history and state to reduce repeated processing overhead.

Streaming Response Support

Coroutines and the message system natively support LLM token-by-token streaming responses.

Tool Call Orchestration

Models tools as independent Actors, supporting concurrent calls, timeout retries, and distributed deployment.

Observability

Provides metrics (OpenMetrics/Prometheus), distributed tracing (W3C TraceContext), and structured logging.

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Section 06

Development Experience: Configuration, CLI, and Protobuf Integration

TOML Configuration Topology

Declares Actor trees and scheduler bindings via TOML files, supporting templates and AOT compilation.

Interactive CLI

CliActor provides a command-line interface, supporting functions like Actor list viewing and metric display.

Protobuf Integration

Natively supports Protobuf serialization with zero-copy potential.

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Section 07

Application Scenarios and Comparison with Existing Solutions

Application Scenarios

  1. High-concurrency AI inference services
  2. Long-running agents
  3. Real-time inference systems
  4. Distributed AI orchestration
  5. Edge AI deployment

Comparison with Existing Solutions

Feature HPActor Python asyncio Java Akka Ray
Language C++20 Python Java/Scala Python/C++
Coroutine C++20 stackless coroutine asyncio Not supported Custom
Memory Management Two-level Slab allocator GC JVM GC Plasma/Custom
Scheduling Hybrid scheduler + EDF Event loop Fork-Join Distributed scheduling
Distributed Built-in Requires additional libraries Akka Cluster Ray Core
Supervision Tree Fully supported None Fully supported Limited
Performance Million-level Actors Ten-thousand-level Hundred-thousand-level Hundred-thousand-level
Application Scenario Low-level inference engine IO-intensive applications Enterprise applications ML workflows
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Section 08

Summary and Outlook: Current Status and Future of HPActor

HPActor combines C++20 features, lock-free data structures, memory management, and distributed support to provide a foundation for next-generation AI service platforms. It is currently in active development, with core systems, schedulers, and network layers already implemented. Future plans include adding cluster control, security architecture, and operation and maintenance planes. Developers of AI inference services requiring extreme performance, reliability, and scalability are advised to pay attention and give it a try.