Ben.BlockingDetector
Blocking Detection for ASP.NET Core
Detect Blocking Calls in ASP.NET Core Applications
Blocking calls can lead to ThreadPool starvation. Outputs a warning to the log when blocking calls are made on the ThreadPool.
Usage
Add early to your ASP.NET Core pipeline (see: samples)
app.UseBlockingDetection();Caveats
Doesn't detect everything... so its not a panacea; you should actively try to avoid using blocking calls.
- For
asyncmethods with occurances of.ConfigureAwait(false), detection won't alert for blockingMonitorcalls after occurences in the case where the returnedTaskwasn't already completed - Won't alert for blocking calls that don't block, like on precompleted
Tasks (e.g. a single smallBody.Write) - Won't alert for blocking that happens in syscalls (e.g.
File.Read(...),Thread.Sleep)
Will detect CLR initiated waits lock,ManualResetEventSlim,Semaphore{Slim},Task.Wait,Task.Result etc; if they do block.
Example
If you had a method like:
[HttpGet("/sync-over-async")]
public static int BlockingTask()
{
// Detected blocking
return MethodAsync().Result;
}
private static async Task<int> MethodAsync()
{
await Task.Delay(1000);
return 5;
}It would output to your log
warn: Ben.Diagnostics.BlockingMonitor[6]
Blocking method has been invoked and blocked, this can lead to threadpool starvation.
at System.Threading.Tasks.Task.InternalWait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
at mvc.HomeController.BlockingTask() <------------------ ** Blocking function **
at lambda_method(Closure , Object , Object[] )
at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionMethodAsync>d__12.MoveNext()
at System.Runtime.CompilerServices.AsyncTaskMethodBuilder.Start[TStateMachine](TStateMachine& stateMachine)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeActionMethodAsync()
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeNextActionFilterAsync>d__10.MoveNext()
...
at Microsoft.AspNetCore.Hosting.Internal.RequestServicesContainerMiddleware.Invoke(HttpContext httpContext)
at Microsoft.AspNetCore.Hosting.Internal.HostingApplication.ProcessRequestAsync(Context context)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.Frame`1.<ProcessRequestsAsync>d__2.MoveNext()
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c__DisplayClass4_0.<OutputAsyncCausalityEvents>b__0()
at Microsoft.AspNetCore.Server.Kestrel.Internal.System.IO.Pipelines.Pipe.<>c.<.cctor>b__67_3(Object o)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.LoggingThreadPool.<>c__DisplayClass6_0.<Schedule>b__0()
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.LoggingThreadPool.<RunAction>b__3_0(Object o)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadPoolWorkQueue.Dispatch()Also catches held locks
120: public Task LockedMethod(HttpContext httpContext)
121: {
122: var response = httpContext.Response;
123: response.StatusCode = 200;
124: response.ContentType = "text/plain";
125: lock (obj) // **********
126: {
127: // locked outside for 1 sec
128: }
129: var s = new string('n', 16);
130: response.ContentLength = s.Length;
131: return response.WriteAsync(s);
132: }Outputs (with some extra formatting)
warn: Microsoft.AspNetCore.Diagnostics.DetectBlocking[6]
Blocking method has been invoked and blocked, this can lead to threadpool starvation.
at Task AoA.Gaia.Startup.LockedMethod(HttpContext httpContext)
in C:\Work\AoA\src\AoA.Gaia\Startup.cs:line 125 ********
at IApplicationBuilder Microsoft.AspNetCore.Builder.UseExtensions.Use(IApplicationBuilder app, Func<HttpContext, Func<Task>, Task> middleware)+() => { }
....
at void Microsoft.AspNetCore.Server.Kestrel.Internal.System.IO.Pipelines.Pipe._scheduleContinuation(object o)
at void Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.LoggingThreadPool.Schedule(Action<object> action, object state)+() => { }
at void Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.LoggingThreadPool.RunAction()+(object o) => { }
at bool System.Threading.ThreadPoolWorkQueue.Dispatch()