mirror of
https://github.com/yhirose/cpp-httplib.git
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yhirose
9bfd2ddf1c
Bring the READMEs and the docs pages (en and ja) in line with the current header: - Fix the client sample that does not compile, the Transfer-Encoding statement for default headers, the verifier callback comment, the thread pool spawn rule, the sanitize_filename description, and the inverted Accept-Encoding sentence. - Describe recent behaviour: TLS errors behind Read/Write failures, Host validation, Connection: close for a body without length, content_reader rules, refused CONNECT, WebSocketClient proxies, CPPHTTPLIB_INTERIM_RESPONSE_MAX_COUNT, the SSE event size limit, and the payload limit of the Stream API. - Complete the API references of WebSocket, WebSocketClient and the stream:: helpers, and the SSE reconnect rules. - Fix cookbook pages: keychain loading on every backend, received Close status, a multipart sample that trusted the client's file name, an echo sample that sent binary as text, SNI, pre-request handler scope, stop() with WebSocket handlers, and the thread pool notes. - Restore the mutex in the LLM app's Chapter 5 code.
70 lines
2.3 KiB
Markdown
70 lines
2.3 KiB
Markdown
---
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title: "S21. Configure the Thread Pool"
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order: 40
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status: "draft"
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---
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cpp-httplib serves requests from a thread pool. By default, the base thread count is the greater of `std::thread::hardware_concurrency() - 1` and `8`, and it can scale up dynamically to 4× that. To set thread counts explicitly, provide your own factory via `new_task_queue`.
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## Set thread counts
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```cpp
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httplib::Server svr;
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svr.new_task_queue = [] {
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return new httplib::ThreadPool(/*base_threads=*/8, /*max_threads=*/64);
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};
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svr.listen("0.0.0.0", 8080);
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```
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The factory is a lambda returning a `TaskQueue*`. Pass `base_threads` and `max_threads` to `ThreadPool` and the pool scales between them based on load. Idle threads exit after a timeout (3 seconds by default).
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## Also cap the queue
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The pending queue can eat memory if it grows unchecked. You can cap it too.
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```cpp
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svr.new_task_queue = [] {
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return new httplib::ThreadPool(
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/*base_threads=*/12,
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/*max_threads=*/0, // disable dynamic scaling
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/*max_queued_requests=*/18);
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};
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```
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`max_threads=0` disables dynamic scaling — you get a fixed `base_threads`. Requests that don't fit in `max_queued_requests` are rejected.
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## Use your own thread pool
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You can plug in a fully custom thread pool by subclassing `TaskQueue` and returning it from the factory.
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```cpp
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class MyTaskQueue : public httplib::TaskQueue {
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public:
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MyTaskQueue(size_t n) { pool_.start_with_thread_count(n); }
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bool enqueue(std::function<void()> fn) override { return pool_.post(std::move(fn)); }
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void shutdown() override { pool_.shutdown(); }
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private:
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MyThreadPool pool_;
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};
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svr.new_task_queue = [] { return new MyTaskQueue(12); };
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```
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Handy when you already have a thread pool in your project and want to keep thread management unified.
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## Compile-time tuning
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You can set the defaults with macros if you want compile-time configuration.
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```cpp
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#define CPPHTTPLIB_THREAD_POOL_COUNT 16 // base thread count
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#define CPPHTTPLIB_THREAD_POOL_MAX_COUNT 128 // max thread count
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#define CPPHTTPLIB_THREAD_POOL_IDLE_TIMEOUT 5 // seconds before idle threads exit
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#include <httplib.h>
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```
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> **Note:** A WebSocket connection holds a worker thread for its entire lifetime. For lots of simultaneous WebSocket connections, raise the maximum thread count (e.g. `ThreadPool(8, 64)`).
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