МСУАлексей КParallel тут ни к чему. Тут к месту Task на базе Async Pattern.
А по попе за параллель? :)


У нас запрос к БД. Выделять поток из пула на ожидание I/O глупо.

dvimВ клиенте СУБД-многопоточность нужна очень редко.Нет. Запуск запросов к серверу (БД, веб-сервис и т. п.) в UI-потоке в наше время считается плохим тоном.

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Алексей К

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авторMonitoring the IAsyncResult’s WaitHandle (as returned from its AsyncWaitHandle property) has a few implications. First, since the APM pattern is all about asynchrony, most IAsyncResult implementations strive to avoid allocating the WaitHandle, only doing so lazily if it’s actually requested. Thus, by accessing the IAsyncResult’s AsyncWaitHandle property, FromAsync is likely forcing allocation of a WaitHandle (and the associated operating system primitives) that otherwise wouldn’t need to be allocated. Second, the only way to “monitor” a WaitHandle to know when it’s been set is to wait on it, which is a potentially blocking operation. Obviously, FromAsync isn’t going to block the current thread by waiting on this handle (that wouldn’t be very async of it), so instead it relies on the ThreadPool. It could queue a work item to block on the handle, but that would end up burning a ThreadPool thread for each such call. Instead, FromAsync relies on ThreadPool.RegisterWaitForSingleObject, a function that is specifically geared towards using the ThreadPool to more efficiently wait for handles. According to the MSDN documentation, it does so by waiting on multiple handles from a single thread via WaitForMultipleObjects; however, there are a limit to how many handles it can wait on from each thread, so while this will end up burning fewer threads than if we blocked one thread per handle, it’s still far from ideal.



async\await не будет ничего блокировать при вызовах асинхронных вариантов методов для БДЧитай внимательнее. Там рядом пример через ContinueWhenAll , без выделения потока на ожидание. Чтобы добиться такого результата необязательно использовать async/await. Достаточно 4-го фреймворка.

SeVaавтор FromAsync relies on ThreadPool.RegisterWaitForSingleObject , a function that is specifically geared towards using the ThreadPool to more efficiently wait for handles. According to the MSDN documentation, it does so by waiting on multiple handles from a single thread via WaitForMultipleObjects; however, there are a limit to how many handles it can wait on from each thread, so while this will end up burning fewer threads than if we blocked one thread per handle, it’s still far from ideal.
Который из них? Их там около десятка.