doc: Add example to use nghttp2::asio_http2::server::request::run_task
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@ -51,8 +51,8 @@ HTTP/2 server looks like this:
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First we instantiate ``nghttp2::asio_http2::server::http2`` object.
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Then call ``nghttp2::asio_http2::server::http2::listen`` function with
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address and port to listen to and callback function invoked when
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request arrives.
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address and port to listen to and callback function, namely "request
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callback", invoked when request arrives.
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The ``req`` and ``res`` represent HTTP request and response
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respectively. ``nghttp2::asio_http2_::server::response::write_head``
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@ -105,11 +105,10 @@ files must be in PEM format.
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In the above example, if request path is either "/" or "/index.html",
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we serve index.html file in the current working directory.
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``nghttp2::asio_http2::server::response::end`` has overload to take
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function of type ``nghttp2::asio_http2::server::read_cb`` and
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application pass its implementation to generate response body. For
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the convenience, libnghttp2_asio library provides
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``nghttp2::asio_http2::server::file_reader`` function to generate
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function to server static file.
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function of type ``nghttp2::asio_http2::read_cb`` and application pass
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its implementation to generate response body. For the convenience,
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libnghttp2_asio library provides ``nghttp2::asio_http2::file_reader``
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function to generate function to server static file.
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Server push
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+++++++++++
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@ -173,3 +172,72 @@ desired number of threads:
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// Use 4 native threads
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server.num_threads(4);
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Run blocking tasks in background thread
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+++++++++++++++++++++++++++++++++++++++
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The request callback is called in the same thread where HTTP request
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is handled. And many connections shares the same thread, we cannot
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directly run blocking tasks in request callback.
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To run blocking tasks, use
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``nghttp2::asio_http2::server::request::run_task``. The passed
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callback will be executed in the different thread from the thread
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where request callback was executed. So application can perform
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blocking task there. The example follows:
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.. code-block:: cpp
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#include <unistd.h>
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#include <nghttp2/asio_http2.h>
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using namespace nghttp2::asio_http2;
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using namespace nghttp2::asio_http2::server;
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int main(int argc, char* argv[])
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{
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http2 server;
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server.num_concurrent_tasks(16);
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server.listen
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("*", 3000,
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[](std::shared_ptr<request> req, std::shared_ptr<response> res)
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{
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req->run_task
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([res](channel& channel)
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{
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// executed in different thread than the thread where
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// request callback was executed.
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// using res directly here is not safe. Capturing it by
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// value is safe because it is std::shared_ptr.
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sleep(1);
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channel.post
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([res]()
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{
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// executed in the same thread where request callback
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// was executed.
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res->write_head(200);
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res->end("hello, world");
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});
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});
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});
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}
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First we set the number of background threads which run tasks. By
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default it is set to 1. In this example, we set it to 16, so 16 tasks
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can be executed in parallel.
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We call ``req->run_task()`` to execute task in background thread. In
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the passed callback, we just simply sleeps 1 second. After sleep is
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over, we schedule another callback to send response to the client.
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Since the callback passed to ``req->run_task()`` is executed in the
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different thread from the thread where request callback is called,
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using ``req`` or ``res`` object directly there may cause undefined
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behaviour. To avoid this issue, we can use
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``nghttp2::asio_http2::channel::post`` by supplying a callback which
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in turn get called in the same thread where request callback was
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called.
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