Definition

public ref class AggregateException : Exception

public class AggregateException : Exception

[System.Serializable]
public class AggregateException : Exception

type AggregateException = class
    inherit Exception

[<System.Serializable>]
type AggregateException = class
    inherit Exception

Public Class AggregateException
Inherits Exception

Inheritance

Attributes

Examples

The following example catches the AggregateException exception and calls the Handle method to handle each exception it contains. Compiling and running the example with the first task1 variable should result in an AggregateException object that contains an UnauthorizedAccessException exception. Commenting out that line, uncommenting the second task1 variable, and compiling and running the example produces an AggregateException object that contains an IndexOutOfRangeException exception.

using System;
using System.IO;
using System.Threading.Tasks;

class Example
{
   static async Task Main(string[] args)
   {
      // Get a folder path whose directories should throw an UnauthorizedAccessException.
      string path = Directory.GetParent(
                              Environment.GetFolderPath(
                              Environment.SpecialFolder.UserProfile)).FullName;

      // Use this line to throw UnauthorizedAccessException, which we handle.
      Task<string[]> task1 = Task<string[]>.Factory.StartNew(() => GetAllFiles(path));

      // Use this line to throw an exception that is not handled.
      // Task task1 = Task.Factory.StartNew(() => { throw new IndexOutOfRangeException(); } );
      try
      {
          await task1;
      }
      catch (UnauthorizedAccessException)
      {
          Console.WriteLine("Caught unauthorized access exception-await behavior");
      }
      catch (AggregateException ae)
      {
          Console.WriteLine("Caught aggregate exception-Task.Wait behavior");
          ae.Handle((x) =>
          {
              if (x is UnauthorizedAccessException) // This we know how to handle.
              {
                  Console.WriteLine("You do not have permission to access all folders in this path.");
                  Console.WriteLine("See your network administrator or try another path.");
                  return true;
              }
              return false; // Let anything else stop the application.
          });
      }

      Console.WriteLine("task1 Status: {0}{1}", task1.IsCompleted ? "Completed," : "",
                                                task1.Status);
   }

   static string[] GetAllFiles(string str)
   {
      // Should throw an UnauthorizedAccessException exception.
      return System.IO.Directory.GetFiles(str, "*.txt", System.IO.SearchOption.AllDirectories);
   }
}
// The example displays the following output if the file access task is run:
//       You do not have permission to access all folders in this path.
//       See your network administrator or try another path.
//       task1 Status: Completed,Faulted
// It displays the following output if the second task is run:
//       Unhandled Exception: System.AggregateException: One or more errors occurred. ---
//       > System.IndexOutOfRangeException: Index was outside the bounds of the array.
//          at Example.<Main>b__0()
//          at System.Threading.Tasks.Task.Execute()
//          --- End of inner exception stack trace ---
//          at System.AggregateException.Handle(Func`2 predicate)
//          at Example.Main(String[] args)

open System
open System.IO
open System.Threading.Tasks

let getAllFiles str =
    // Should throw an UnauthorizedAccessException exception.
    System.IO.Directory.GetFiles(str, "*.txt", System.IO.SearchOption.AllDirectories)

// Get a folder path whose directories should throw an UnauthorizedAccessException.
let path =
    let directory =
        Environment.SpecialFolder.UserProfile
        |> Environment.GetFolderPath
        |> Directory.GetParent
    directory.FullName

// Use this line to throw an exception that is not handled.
// let task1 = Task<string []>.Factory.StartNew(fun () -> raise (IndexOutOfRangeException()) )
let task1 = Task.Factory.StartNew(fun () -> getAllFiles (path))

let execute () =
    try
        task1.Wait()
    with
    | :? UnauthorizedAccessException -> printfn "Caught unauthorized access exception-await behavior"
    | :? AggregateException as ae ->
        printfn "Caught aggregate exception-Task.Wait behavior"

        ae.Handle (fun x ->
            match x with
            | :? UnauthorizedAccessException ->
                printfn "You do not have permission to access all folders in this path."
                printfn "See your network administrator or try another path."
                true
            | _ -> false)
    printfn $"""task1 Status: {if task1.IsCompleted then "Completed," else ""}{task1.Status}"""

execute ()

// The example displays the following output if the file access task is run:
//       You do not have permission to access all folders in this path.
//       See your network administrator or try another path.
//       task1 Status: Completed,Faulted
// It displays the following output if the second task is run:
//       Unhandled exception. System.AggregateException: One or more errors occurred. (Index was outside the bounds of the array.) (Index was outside the bounds of the array.)
//        ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
//          at Exception1.task1@19.Invoke()
//          at System.Threading.Tasks.Task`1.InnerInvoke()
//          at System.Threading.Tasks.Task.<>c.<.cctor>b__277_0(Object obj)
//          at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)   
//       --- End of stack trace from previous location ---
//          at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)   
//          at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
//          --- End of inner exception stack trace ---
//          at System.AggregateException.Handle(Func`2 predicate)
//          at <StartupCode$exception1>.$Exception1.main@()

Imports System.IO
Imports System.Threading.Tasks

Module Example
    Sub Main()
        ' Get a folder path whose directories should throw an UnauthorizedAccessException.
        Dim path As String = Directory.GetParent(
                                       Environment.GetFolderPath(
                                       Environment.SpecialFolder.UserProfile)).FullName

        ' Use this line to throw UnauthorizedAccessException, which we handle.
        Dim task1 = Task(Of String()).Factory.StartNew(Function() GetAllFiles(path))

        ' Use this line to throw an exception that is not handled.
        ' Task task1 = Task.Factory.StartNew(Sub() Throw New IndexOutOfRangeException() )
        Try
            task1.Wait()
        Catch ae As AggregateException
            ae.Handle(Function(x)
                          If TypeOf (x) Is UnauthorizedAccessException Then ' This we know how to handle
                              Console.WriteLine("You do not have permission to access all folders in this path.")
                              Console.WriteLine("See your network administrator or try another path.")
                              Return True
                          Else
                              Return False ' Let anything else stop the application.
                          End If
                      End Function)
        End Try

      Console.WriteLine("task1 Status: {0}{1}", If(task1.IsCompleted, "Completed,", ""), 
                                                task1.Status)
    End Sub

    Function GetAllFiles(ByVal str As String) As String()
        ' Should throw an UnauthorizedAccessException exception. 
        Return System.IO.Directory.GetFiles(str, "*.txt", System.IO.SearchOption.AllDirectories)
    End Function
End Module

AggregateException is used to consolidate multiple failures into a single, throwable exception object. It is used extensively in the Task Parallel Library (TPL) and Parallel LINQ (PLINQ). For more information, see Exception Handling and How to: Handle Exceptions in a PLINQ Query. For additional information, see the Aggregating Exceptions entry in the .NET Matters blog.

Thread Safety

All public and protected members of AggregateException are thread-safe and may be used concurrently from multiple threads.