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title, order, status
| title | order | status |
|---|---|---|
| S20. Tune Keep-Alive | 39 | draft |
httplib::Server enables HTTP/1.1 Keep-Alive automatically. From the client's perspective, connections are reused — so they don't pay the TCP handshake cost on every request. When you need to tune the behavior, there are two setters.
What you can configure
| API | Default | Meaning |
|---|---|---|
set_keep_alive_max_count |
100 | Max requests served over a single connection |
set_keep_alive_timeout |
5s | How long an idle connection is kept before closing |
Basic usage
httplib::Server svr;
svr.set_keep_alive_max_count(20);
svr.set_keep_alive_timeout(10); // 10 seconds
svr.listen("0.0.0.0", 8080);
set_keep_alive_timeout() also has a std::chrono overload.
using namespace std::chrono_literals;
svr.set_keep_alive_timeout(10s);
Tuning ideas
Too many idle connections eating resources
Shorten the timeout so idle connections drop and release their worker threads.
svr.set_keep_alive_timeout(2s);
API is hammered and you want max reuse
Raising the per-connection request cap improves benchmark numbers.
svr.set_keep_alive_max_count(1000);
Never reuse connections
Set set_keep_alive_max_count(1) and every request gets its own connection. Mostly only useful for debugging or compatibility testing.
Relationship with the thread pool
A Keep-Alive connection holds a worker thread for its entire lifetime. If connections × concurrent requests exceeds the thread pool size, new requests wait. For thread counts, see S21. Configure the thread pool.
Note: For the client side, see C14. Understand connection reuse and Keep-Alive behavior. Even when the server closes the connection on timeout, the client reconnects automatically.