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Building a High-Performance C++ Server with Networking TS: A Deep Dive into Asynchronous Design

• 0:00:02 Networking with Experts: The speaker emphasizes the value of direct interaction with C++ experts like Bjarne Stroustrup and Sean Parent at CppCon.

• 0:00:35 Learning Imbalance: The speaker observes a common issue in learning materials: an overemphasis on either theory or practical application, without a balanced approach.

• 0:00:48 Real-world vs. Theory: University students often experience learning pure theory that lacks real-world application, while software documentation often provides small, isolated examples without guidance on building large-scale systems.

• 0:01:30 Application Tour: The goal is to guide the audience through building a real-world application using the Networking TS, from low-level details to a high-level, functional server.

• 0:01:52 Use Case: Market Data Server: The application is a backend component of a larger system. It receives client queries (via HTTP or WebSockets) for market data and returns responses. A "router" component handles heterogeneous queries and directs them to the appropriate backend.

• 0:02:23 Backend Implementation: The focus is on the backend, built using the Networking TS (Boost.Asio) and a proprietary, in-house, file-based time-series database.

• 0:02:52 Proprietary Protocol: Datacon: A custom protocol ("Datacon") is used for internal communication, prioritizing low latency and high throughput. It supports request/response semantics and allows for streaming large responses (gigabytes or terabytes).

• 0:03:50 Datacon Utilities: The data con protocol allows reusing back-end connections to allow front end to cancel unneeded responses and keeping idle connections active.

• 0:04:30 Datacon Message Structure: Datacon messages have a 5-byte header (4 bytes for length, 1 byte for message type), followed by a free-form body. The message type defines the vocabulary (e.g., request, cancel, acknowledge, reject, intermediate chunk, final chunk, error, heartbeat).

• 0:08:19 Teaching Networking TS Datacon: The process begins by enumerating message types, then design the async_read operation.

• 0:08:38 Dynamic Buffers: Unlike previous uses of const/mutable buffer sequences, dynamic buffers are needed because the exact size of the message is unknown at the start.

• 0:11:08 Denial of Service (DoS) Protection: The max_size member of a dynamic buffer is treated as a policy to prevent excessive memory allocation in response to malicious input. The async_read_grow helper function checks for potential overflows and returns an error if necessary.

• 0:13:49 async_read Completion: The async_read operation doesn't return a value directly but invokes a completion handler with an error code, bytes transferred, message type, and a view into the dynamic buffer.

• 0:15:29 async_write Design: Complementary to async_read, an async_write_state type alias is used for preparing the header. async_write takes the stream, message type, write state, payload view, and completion token.

• 0:17:03 Building Up, Not Monolithically: The design emphasizes building small, reusable components and composing them, promoting code reuse (e.g., creating a Datacon command-line debugger).

• 0:17:59 Heartbeat Implementation (async_heartbeat): This operation handles sending heartbeats to keep the connection alive. It always fails eventually (connections always end in failure). The heartbeat_events named type requirement allows injecting logic for determining the delay between heartbeats and notifying when a heartbeat is sent.

• 0:22:05 Datacon State Transitions: The core logic of Datacon is represented as a state transition diagram (idle, waiting for request, sending response, after response).

• 0:22:39 "After Response" State: This state accounts for the inherent latency in network communication and potential race conditions between a client canceling a response and the server finishing the response.

• 0:24:17 async_control Operation: This high-level operation encapsulates the Datacon state transition logic. It uses control_events to customize behavior (e.g., completing writes, canceling responses, initializing requests).

• 0:25:54 async_control_events Details: This includes async_start_write (an asynchronous callback to start writing), async_run (to send response chunks), and async_wait (for polling non-blocking implementations).

• 0:29:12 Non-Reentrancy: The Networking TS guarantees non-reentrancy (completion handlers are not invoked below the initiating function). However, this can be relaxed for injected asynchronous callbacks (like async_start_write) when the underlying operation already provides the guarantee.

• 0:30:45 Query Driver: This component manages the underlying query object and handles heartbeats and control events. It uses a sticky_cancel_async_stream to ensure cancellation is persistent.

• 0:32:46 Query Interface: The final user-defined component, a query, provides methods for initialization (init), incremental work (run), cancellation (end), payload retrieval (payload), and buffer toggling (toggle).

• 0:34:01 Buffer Toggling: Double buffering (toggle) is used to maximize CPU/network/disk utilization. While one buffer is being sent over the network, the other is being filled with data.

• 0:35:50 Connection Management: The async_accept operation handles accepting incoming connections. It uses accept_events, especially next_context, to bind each connection to a specific execution context (thread), enabling single-threaded processing per connection.

• 0:37:52 Thread Pool: A thread pool is created for managing worker threads and providing execution contexts.

• 0:38:49 run_server Function: This final glue code brings everything together. It sets up the thread pool, acceptors (for IPv4/IPv6), and kicks off async_accept and async_control.

• 0:45:13 Context Transition: The on_accept lambda (for accepted connections) uses asio::execution::execute to switch to the correct execution context (the one associated with the accepted stream).

• 0:46:52 Server Run Loop A signal set is createad that handles sigin and sig term signals to enable graceful shut down.

• 0:48:21 Production Deployment: The presented design and code are not theoretical but are part of a system running in production.

• 0:49:00 Q&A: Toggle vs. Queue: Toggle is preferred over a queue to avoid coupling to a specific data structure. A queue could be a valid implementation detail, but async_control might assume only two buffers.

• 0:50:35 Q&A: Adding TLS Support: run_server is a concrete implementation with specific choices, so it can't directly support TLS. But, the rest of the framework works with async_read_stream, async_write_stream, and async_stream. If an SSL Stream exists, it could be added.