How to Reset the Conversation in Needle: Two Methods Explained

Call needle.reset() in Python or POST to /reset on the playground server to clear all conversation state and start fresh.

Needle is a lightweight LLM inference engine that maintains internal state across prompts—including token history, context windows, and cached model data. When you need to start a new conversation without residual context, you must explicitly reset this state. This guide covers both programmatic and HTTP-based approaches to reset the conversation in Needle, with direct references to the source implementation in cactus-compute/needle.

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Why Conversation State Matters in Needle

Unlike stateless APIs, Needle's engine accumulates context across generate() calls to support multi-turn conversations. This improves coherence but means previous prompts influence subsequent outputs. Resetting wipes all in-memory buffers, token streams, and cached model state according to the C-extension implementation in needle/__init__.py.

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Method 1: Programmatic Reset via Python API

The Needle class exposes a reset() method that forwards directly to the underlying C library. This is the preferred approach when embedding Needle in applications.

Calling reset() on a Needle Instance

import needle

# Initialize the engine

nl = needle.Needle(model="gpt2")

# Run prompts that build context

print(nl.generate("Hello, my name is Alice."))
print(nl.generate("What's my name?"))  # Responds based on previous context

# Clear all conversation state

nl.reset()  # ← wipes token history and context windows

# New conversation starts fresh

print(nl.generate("What's my name?"))  # No knowledge of "Alice"

Implementation Details

In needle/__init__.py, the reset() method delegates to needle_reset():

# Located at needle/__init__.py#L153

def reset(self):
    """Reset the conversation state and clear all caches."""
    lib.needle_reset()

The C function binding is declared earlier in the same file:

# Located at needle/__init__.py#L47

lib.needle_reset.argtypes = []
lib.needle_reset.restype = None

This function has no arguments and returns nothing—it performs a complete state wipe at the C level.

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Method 2: HTTP Reset via the Playground Server

Needle includes a built-in playground server for testing and integration. The /reset endpoint provides remote state clearing.

Sending a Reset Request

# Reset conversation state

curl -X POST http://localhost:8000/reset

# Subsequent requests start fresh

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"prompt":"Tell me a joke"}' \
  http://localhost:8000/generate

Server Implementation

The endpoint handler in needle/playground/server.py routes the request to the engine's reset() method:

# Located at needle/playground/server.py#L141

elif self.path == "/reset":
    engine.reset()  # Delegates to same C-extension routine

    self.send_response(200)
    self.end_headers()

Both paths ultimately invoke lib.needle_reset(), ensuring identical behavior.

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Key Source Files and Functions

Understanding the implementation helps debug reset issues and verify behavior:

File	Function/Line	Purpose
needle/__init__.py	def reset(self) at L153	Python wrapper method calling C extension
needle/__init__.py	lib.needle_reset binding at L47	C function argument/return type declarations
needle/playground/server.py	/reset endpoint at L141	HTTP route handling
tests/test_weights.py	self.calls.append("reset") at L28	Unit test verification of reset propagation

The test suite confirms that reset() calls are properly tracked and propagated through the stack, as shown in tests/test_weights.py.

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Choosing Between Methods

• Use the Python API when building applications, scripts, or automated pipelines where you control the Needle instance lifecycle.
• Use the HTTP endpoint when integrating with external services, testing via curl, or running Needle as a microservice.

Both methods execute the same low-level routine, so performance and completeness are identical.

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Summary

• Primary method: Call nl.reset() on any Needle instance to clear conversation state programmatically.
• HTTP alternative: POST to /reset on the playground server for remote resets.
• Common implementation: Both paths invoke lib.needle_reset() defined in needle/__init__.py, which wipes all in-memory state at the C level.
• Verification: Unit tests in tests/test_weights.py confirm proper reset propagation.

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Frequently Asked Questions

What happens if I don't reset between conversations?

Without resetting, Needle retains token history and context windows from previous prompts. This causes new prompts to be influenced by earlier conversation turns, which may produce confusing or incorrect responses when switching topics or users.

Is reset() synchronous or asynchronous?

The reset() method is synchronous and blocks until the C-extension completes state clearing. There is no async variant in the current implementation—all buffer operations happen immediately in the calling thread.

Does resetting affect the loaded model weights?

No. needle_reset() only clears conversation-specific state: token buffers, generation history, and context caches. The model weights remain loaded in memory, so subsequent generate() calls execute immediately without reloading.

Can I reset state from multiple threads safely?

The C-extension's needle_reset() is not explicitly documented as thread-safe in the source. For multi-threaded applications, external synchronization is recommended—wrap reset() calls with appropriate locks to prevent race conditions with ongoing generate() operations.

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