asynchrony in (asp).net aliaksandr
DESCRIPTION
1.Wait 2.Make someone to wait 3.Check periodically 4.Make someone to check 5.Put a whistle on a kettle 6.Add a web-interface to a kettle 1.Sync 2.Sync with threads 3.Async-sync 4.Async with threads 5.Async with callbacks 6.Async with eventsTRANSCRIPT
Developer and a Kettle
Developer and a Kettle
1. Wait2. Make someone to wait3. Check periodically4. Make someone to
check5. Put a whistle on a
kettle6. Add a web-interface to
a kettle
1. Sync2. Sync with threads3. Async-sync4. Async with threads
5. Async with callbacks
6. Async with events
Comparison
Approach Transferring 1K,rps
Transferring 1M,rps
Sync 2844,44 100% 32,57 26%
Async with callbacks 2547,26 90% 125,97 100%
Async-sync 2327,28 82% 33,04 26%
Sync with threads 861,23 30% 83,89 67%
Async with threads 604,84 21% 80,36 64%
Evolution: WinAPI• struct OVERLAPPED (IAsyncResult)
• OVERLAPPED_COMPLETION_ROUTINE
(AsyncCallback)
6
Evolution: .NET 1.0 – 1.1• IAsyncResult
• AsyncCallback
• BeginXXX(@params, callback, userState)
• EndXXX(asyncResult)
7
Evolution: .NET 2.0 – … • event XXXCompleted
• XXXCompletedEventArgs
• EventHandler<XXXCompletedEventArgs
>
• XXXAsync(@params, userState)
• CancelAsync()
• AsyncOperationManager
• AsyncOperation
• SyncronizationContext
Evolution: .NET 4.0
• Task Parallel Library
IAsyncResult vs Events
IAsyncResult1. Callbacks are not thread
safe2. No context in callbacks (i.e.
no HttpContext)
3. Complexity of chaining (custom IAsyncResult, etc.)
4. Poor support of components
Events1. Event handlers are under
lock2. HttpContext available
3. Chaining is simple4. Component-oriented
ContextAwareResult, but no guarantee
SyncronizationContext
Event-based async pattern
Thread #1 XAsync YAsync
Thread #3 YCompleted
Thread #2 ZAsync
Thread #4 ZCompleted
PreRenderComplete
PreRender
AsyncOperationManagerX Y
XCompleted
Z
All operations arecompleted
TTT #1: Use closures var asyncResult = component.BeginSomeOperation(parameter, aresult => TrickyCallback(aresult, component), state);
void TrickyCallback(IAsyncResult state, Component component){ bool result = component.EndOperation(state);}
TTT#2: Use userState carefullystatic void Main(string[] args){ var asyncResult = component.BeginSomeOperation(
parameter, Callback, state);}
void Callback(IAsyncResult aresult){ bool result = component.EndOperation(aresult); object state = asyncResult.AsyncState;}
TTT#3: Unsubscribe from eventsstatic void Main(string[] args){ component.OperationCompleted += component_OperationCompleted; component.OperationAsync("data", null);}
static void component_OperationCompleted(object sender, EventArgs e){ component.OperationCompleted -= component_OperationCompleted;}
TTT#5: There is no timeout support in both async patterns
TTT#6 AsyncResult callbacks don’t have HttpContext
• It could be, but there is no guarantee
TTT#7 Do not convert event-based pattern to IAsyncResult one
• Event-based pattern uses locks, that could be not desirable
TTT #8: Do not use [ThreadStatic]
• Do not forget about ThreadPool
TTT#9: Do not throw exceptions in callbacks
• Even WSE 3.0 has had a bug we had spotted.
Q&A