## Event Loop and Thread Pool interaction
|
|
The CppCMS service has a simple design of a single event
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loop, and a thread pool that handles actual user
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application responses.
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Every new incoming FastCGI, SCGI or HTTP request
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is accepted by the CppCMS service and handled
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by the fast and efficient CppCMS event loop that is
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based on `epoll`, `kqueue`, `/dev/poll` or `select`
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system calls.
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|
On an incoming request, a special HTTP Context is created.
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It prepares the incoming request, reads all POST data and
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if required parses it within the central event loop.
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Once the request is ready, it is checked against the
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CppCMS applications pool to detect which
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application object handles it.
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If the application that handles it is a synchronous
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application, its execution is passed to the
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_thread pool_. The user application prepares the response
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and sends it synchronously to the client and the context
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is destroyed, completing the "request/response" cycle.
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If the application is asynchronous, the HTTP Context
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remains inside the event loop's thread and it is handled by
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the asynchronous application. This application
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may decide to complete the response immediately
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or postpone it by implementing, for example, long polling.
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## Integration with CppCMS Event Loop
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|
There are several ways to interact with the event loop,
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besides the obvious - implementing your own asynchronous
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application:
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1. Use the `cppcms::service::get_io_service()` function
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to access the event loop directly.
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You can use any of the [`booster::aio`](/cppcms_ref_v0_99/namespacebooster_1_1aio.html) classes there
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and handle various asynchronous events.
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2. You can post various operations for execution
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in the event loop using `cppcms::service::post()`
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from other threads.
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This is especially important when you want to
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do integration between synchronous and asynchronous
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applications.
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You should remember that most of the CppCMS objects
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including `http::context` are not thread safe
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for access from multiple threads, so
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if some operation should be executed on
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objects running in the event loop, it must
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be done by posting handlers for execution
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in the event loop.
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It is important to remember that
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every operation executed in the event
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loop should be _very fast_ and _never block_.
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---
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← [CppCMS 1.x.x Configuration][prev]
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| [Top](#maincontent)
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| [Understanding Application Lifetime][next] →
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|
[prev]: /wikipp/en/page/cppcms_1x_config
|
[next]: /wikipp/en/page/cppcms_1x_application_lifetime |
