exception-based-comms

A proof‑of‑concept speed test demonstrating IPC via custom Windows exceptions and the Debugging API.
WARNING: This is VERY hacky and fragile.

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Table of Contents

• Overview
• Features
• Prerequisites
• Building
• Usage
• How It Works
• Performance Results
• Limitations & Warnings
• Contributing
• License

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Overview

This project launches two copies of the same executable in “speed” mode. They negotiate roles (server/client) through a shared memory mapping, then perform two rounds of message exchange:

1. Round 1: Server raises a custom exception repeatedly; client attaches as debugger and counts exceptions.
2. Round 2: Roles swap.

The tool prints the throughput (messages per second) for each round.

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Features

• Role negotiation via a named FileMapping
• Custom exception code (0x1337) to carry a pointer+length
• Two‑phase speed test with bidirectional measurements
• Outputs precise timing (using QueryPerformanceCounter)

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Prerequisites

• Windows 7 or later
• MSVC (Visual Studio) or any compiler supporting Win32 APIs
• Administrator privileges may be required to debug another process

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Building

1. Clone the repo:

   git clone https://github.com/Smellon69/exception-based-comms.git
   cd exception-based-comms

2. Open the solution/existing project in Visual Studio, or compile via command line:

   cl.exe /EHsc main.cpp /link /out:main.exe

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Usage

# Launch first instance (server):
exception-based-comms.exe speed

# Launch second instance (client) within 10 seconds:
exception-based-comms.exe speed

You’ll see output like:

Role: server (PID 1234)
Connected to PID 5678

Round 1 (server sends, client debugs):
Server: sent 10000 messages in 0.12s (83333 msg/s)

Round 2 (server debugs client):
Server debugger: attached to PID 5678
Server debugger: detached from PID 5678

Speed test complete.

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How It Works

1. Shared Memory
   A CreateFileMapping named "Global\\UDCommMapping" holds two PIDs for role negotiation.
2. Exception‑Based Messaging
   RaiseException(0x1337, …) carries the message pointer/length.
3. Debug Loop
   The debugging process uses WaitForDebugEvent/ContinueDebugEvent to catch and count exception events.
4. Timing
   Uses QueryPerformanceCounter for high‑resolution measurement.

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Performance Results

Round	Role	Throughput (msg/s)
Round 1	Server send	83 333
Round 2	Client send	79 214

Results will vary significantly based on CPU, OS version, and debugger overhead.

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Contributing

1. Fork the repo
2. Create a new branch (git checkout -b feature/your‑idea)
3. Commit your changes
4. Open a Pull Request

Please keep comments concise and follow Google’s C++ Style Guide.

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License

This project is licensed under the MIT License. See LICENSE for details.