Implementation:LMCache LMCache Multiprocess Protocol

Knowledge Sources	LMCache
Domains	Inter-Process Communication, RPC Protocol
Last Updated	2026-02-09 00:00 GMT

Overview

This module defines the RPC protocol for communication between LMCache core server and worker clients, specifying request types, payload structures, and handler types.

Description

The protocol is organized around a RequestType enum that enumerates all supported operations: REGISTER_KV_CACHE, UNREGISTER_KV_CACHE, STORE, RETRIEVE, LOOKUP, CLEAR, GET_CHUNK_SIZE, and NOOP. Each request type maps to a ProtocolDefinition that declares the expected payload classes, response class, and handler type. Handler types include SYNC (runs directly in the main loop), BLOCKING (runs in a thread pool), and NON_BLOCKING (reserved for future use). Helper functions get_payload_classes, get_response_class, and get_handler_type provide lookup access to the protocol definitions. The key type used throughout the protocol is IPCCacheEngineKey.

Usage

Use this module when implementing or extending the multiprocess RPC layer between LMCache workers and the core cache server. The protocol definitions drive message encoding/decoding and handler dispatch.

Code Reference

Source Location

• Repository: LMCache
• File: lmcache/v1/multiprocess/protocol.py
• Lines: 1-172

Signature

class RequestType(enum.Enum):
    REGISTER_KV_CACHE = ...
    UNREGISTER_KV_CACHE = ...
    STORE = ...
    RETRIEVE = ...
    LOOKUP = ...
    CLEAR = ...
    GET_CHUNK_SIZE = ...
    NOOP = ...

class HandlerType(enum.Enum):
    SYNC = ...
    BLOCKING = ...
    NON_BLOCKING = ...

@dataclass
class ProtocolDefinition:
    payload_classes: list[Any]
    response_class: Optional[Any]
    handler_type: HandlerType

def get_payload_classes(req_type: RequestType) -> list[Any]: ...
def get_response_class(req_type: RequestType) -> Optional[Any]: ...
def get_handler_type(req_type: RequestType) -> HandlerType: ...

Import

from lmcache.v1.multiprocess.protocol import (
    RequestType,
    HandlerType,
    ProtocolDefinition,
    get_payload_classes,
    get_response_class,
    get_handler_type,
    KeyType,
    InstanceID,
)

I/O Contract

Inputs

Name	Type	Required	Description
req_type	RequestType	Yes	The request type to look up in the protocol definitions

Outputs

Name	Type	Description
get_payload_classes	list[Any]	List of expected payload types for the given request
get_response_class	Optional[Any]	Expected response type, or None if the request has no response
get_handler_type	HandlerType	Whether the handler is SYNC, BLOCKING, or NON_BLOCKING

The protocol defines the following operations:

Request Type	Payload	Response	Handler
REGISTER_KV_CACHE	[int, KVCache]	None	SYNC
UNREGISTER_KV_CACHE	[int]	None	SYNC
STORE	[list[KeyType], int, list[int], bytes]	tuple[bytes, bool]	BLOCKING
RETRIEVE	[list[KeyType], int, list[int], bytes]	tuple[bytes, list[bool]]	BLOCKING
LOOKUP	[list[KeyType], Optional[bool]]	list[bool]	BLOCKING
CLEAR	[]	None	BLOCKING
GET_CHUNK_SIZE	[]	int	SYNC
NOOP	[]	str	SYNC

Usage Examples

from lmcache.v1.multiprocess.protocol import RequestType, get_payload_classes, get_handler_type

# Look up protocol definition for STORE
payload_types = get_payload_classes(RequestType.STORE)
handler = get_handler_type(RequestType.STORE)
print(f"STORE payload: {payload_types}, handler: {handler}")