Thread Safety
Rule of Thumb
All classes are not thread safe for access from multiple threads simultaneously unless it is stated explicitly otherwise.
In general there are several thread safe classes in the CppCMS that their member functions can be accessed simultaneously from several threads:
cppcms::servicecppcms::applications_poolcppcms::thread_poolcppcms::views::poolbooster::aio::io_service
In all other cases special measures should be taken in order to prevent accessing same class from multiple threads.
Threads in CppCMS
There are several types of threads in CppCMS:
- Event Loop - the main thread, the thread that runs
the
cppcms::service::run()threads. - Thread Pool - the special pool of threads that every synchronous requests are executed there
- Some background threads auxiliary threads that are in general of no interest to you.
Cross Thread Interactions
Once the CppCMS service started all synchronous applications are executed in the thread pool.
If CppCMS synchronous application wants to perform
some operation withing event loop, for example,
interact with some asynchronous application by
sending some data or by transferring its HTTP
context to it, it should do it using
cppcms::service::post() member function
and an appropriate execution handler.
This handler would be dispatched to the event loop queue and executed in its thread.
If asynchronous application or any other object that runs in the event wants to execute some long running, blocking or heavy operation, it may do it by submitting an execution handler to the thread pool.
Note, once the job is complete, the handler should notify its completion by posting some handler to the event loop, the same way as described above.
Different applications should never access their internal states directly as it is not safe.
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