Is io_context::run() blocking?

Yes—it blocks until there is no more work (unless stopped). Multiple threads may call run() to form a thread pool.

Boost.Asio vs standard networking?

Historically Asio (and Networking TS) filled the gap; check your compiler’s experimental networking support for “std” networking.

What if the async buffer is destroyed before completion?

Undefined behavior—keep buffers alive with shared_ptr or tie lifetime to the connection object.

When do I need a strand?

To serialize handlers touching the same socket from multiple threads; alternative designs use a single-threaded io_context or explicit mutexes.

[2026] Boost.Asio Introduction: io_context, async_read, and Non-Blocking I/O

2026년 3월 12일 · 22분 읽기 · 수정 2026년 3월 12일 Intermediate tutorial

이 글의 핵심

Learn Asio: why async beats one-thread-per-connection, io_context and run(), steady_timer, async_read/async_write/async_read_until, async_accept echo server, error_code handling, shared_ptr buffers, and strands.

Introduction: why async I/O?

Blocking `read` ties up a thread per connection—thousands of connections ⇒ thousands of threads. Asio registers async_* operations; io_context::run() dispatches completions so few threads handle many connections. Prerequisite: socket basics (#28).
Requirements: Boost.Asio or standalone Asio, C++14+.

Blocking vs async (diagrams in original)

Blocking: thread waits in read_some. Async: thread runs handlers when data is ready; I/O wait does not consume thread stack.

io_context, post, dispatch, run

post: queue a handler.
dispatch: run immediately if already inside run(); else queue.
run: block until no pending work.
poll / poll_one: non-blocking progress.
restart: after run() returns, reset before run() again.

Async timer

steady_timer::async_wait—chain re-arm in the handler for periodic ticks. Combine with socket.cancel() for read timeouts.

async_read / async_write

async_read: fills buffer completely (or EOF).
async_read_some: partial read—typical for protocols.
async_read_until: delimiter (e.g. newline) into streambuf. Keep shared_ptr to std::array, std::string, or streambuf across the async call.

Async client flow

`async_resolve` → `async_connect` → `async_write` → `async_read`—chain lambdas or bind to session methods.

Async server

async_accept → construct Session with shared_ptr + enable_shared_from_this → async_read_until loop → async_write echo → re-issue read. Always schedule the next async_accept in the handler.

Error handling

Check error_code; treat asio::error::eof as normal close; operation_aborted after cancel; log connection_reset, broken_pipe.

Common mistakes

Dangling this in handlers—use shared_from_this.
run() exits after one connection—re-accept or work_guard.
Stack buffer in async—use heap shared_ptr storage.
run() twice without restart—no work processed second time.
Same socket from multiple threads without strand—data races.

Performance (illustrative)

Async often achieves much higher req/s than one-thread-per-connection at large connection counts—always measure on your workload.

Event loop #29-2
Asio deadlock debugging
Multithread server #29-3 Next: Event loop #29-2 Previous: Network errors #28-3