1811: Unhandled Exception Handling for Parallel Iterations in C#

Encoding QR Code ISO/IEC18004 in C# 1811: Unhandled Exception Handling for Parallel Iterations
Listing 1811: Unhandled Exception Handling for Parallel Iterations
Printing QR-Code In Visual C#.NET
Using Barcode generator for Visual Studio .NET Control to generate, create QR Code image in .NET framework applications.
using using using using System; SystemCollectionsGeneric; SystemIO; SystemThreading;
Barcode Creator In C#.NET
Using Barcode generation for Visual Studio .NET Control to generate, create bar code image in Visual Studio .NET applications.
class Program { // static void EncryptFiles( string directoryPath, string searchPattern) { IEnumerable<string> files = DirectoryGetFiles( directoryPath, searchPattern, SearchOptionAllDirectories); try
QR Code ISO/IEC18004 Drawer In Visual Studio .NET
Using Barcode drawer for ASP.NET Control to generate, create QR-Code image in ASP.NET applications.
Executing Iterations in Parallel
Create QR Code ISO/IEC18004 In .NET Framework
Using Barcode generator for Visual Studio .NET Control to generate, create QR Code image in VS .NET applications.
{ ParallelForEach(files, (fileName) => { Encrypt(fileName); }); } catch (AggregateException exception) { ConsoleWriteLine( "ERROR: {0}:", exceptionGetType()Name); foreach (Exception item in exceptionInnerExceptions) { ConsoleWriteLine(" {0} - {1}", itemGetType()Name, itemMessage); } } } // }
QR-Code Generator In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create QR Code JIS X 0510 image in .NET framework applications.
OUTPUT 187:
Barcode Printer In C#
Using Barcode generation for .NET Control to generate, create barcode image in .NET applications.
ERROR: AggregateException: UnauthorizedAccessException - Attempted to perform an unauthorized operation UnauthorizedAccessException - Attempted to perform an unauthorized operation UnauthorizedAccessException - Attempted to perform an unauthorized operation
Drawing Barcode In Visual C#
Using Barcode generator for Visual Studio .NET Control to generate, create bar code image in VS .NET applications.
Output 187 shows that three exceptions occurred while executing the ParallelForEach<T>() loop However, in the code, there is only one catch of type SystemAggregationException The UnauthorizedAccessExceptions were retrieved from the InnerExceptions property on the AggregationException With a ParallelForEach<T>() loop, each iteration could potentially throw an exception and so the SystemAggregationException thrown by the method call will contain each of those exceptions within its InnerExceptions property
Drawing Code 39 Extended In Visual C#.NET
Using Barcode generation for VS .NET Control to generate, create Code 39 Full ASCII image in VS .NET applications.
Canceling a Parallel Loop Unlike a task which requires an explicit call in order to block until it completes, a parallel loop executes iterations in parallel but still blocks until
Make Code 128 In Visual C#.NET
Using Barcode printer for VS .NET Control to generate, create Code 128A image in VS .NET applications.
18: Multithreading
Making Data Matrix 2d Barcode In C#
Using Barcode encoder for .NET Control to generate, create Data Matrix image in Visual Studio .NET applications.
the entire ParallelFor() or ParallelForEach<T>() loop completes Canceling a parallel loop, therefore, generally involves invocation of the cancellation request from a thread other than the one executing the parallel loop In Listing 1812, we invoke ParallelForEach<T>() using TaskFactoryStartNew() In this manner, not only does the query execute in parallel, but it also executes asynchronously, allowing the code to prompt the user to Push ENTER to exit
Printing Barcode In Visual Studio .NET
Using Barcode creator for ASP.NET Control to generate, create barcode image in ASP.NET applications.
Listing 1812: Canceling a Parallel Loop
Bar Code Generator In .NET
Using Barcode maker for .NET framework Control to generate, create barcode image in .NET applications.
using using using using System; SystemDiagnostics; SystemThreading; SystemThreadingTasks;
USS-128 Generator In .NET Framework
Using Barcode maker for ASP.NET Control to generate, create EAN / UCC - 14 image in ASP.NET applications.
public class Program { // static void EncryptFiles( string directoryPath, string searchPattern) { IEnumerable<string> files = DirectoryGetFiles( directoryPath, searchPattern, SearchOptionAllDirectories); CancellationTokenSource cts = new CancellationTokenSource(); ParallelOptions parallelOptions = new ParallelOptions { CancellationToken = ctsToken }; ctsTokenRegister( () => ConsoleWriteLine("Cancelling")); ConsoleWriteLine("Push ENTER to exit"); Task task = TaskFactoryStartNew(() => { try { ParallelForEach( files, parallelOptions, (fileName, loopState) => { Encrypt(fileName); });
Scan Barcode In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
Executing Iterations in Parallel
UPC - 13 Encoder In VS .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create GS1 - 13 image in VS .NET applications.
} catch(OperationCanceledException){} }); // Wait for the user's input ConsoleRead(); // Cancel the query ctsCancel(); ConsoleWrite(stars); taskWait(); } }
Printing Bar Code In Java
Using Barcode generation for Java Control to generate, create bar code image in Java applications.
The parallel loops use the same cancellation token pattern that Tasks use The CancellationTokenSourceToken property is associated with the parallel loop via overloads on the parallel loops overloads that take a SystemThreadingParallelOptions object This object includes a Token property of type CancellationTokenSource Note that internally the parallel loop case prevents new iterations that haven t started yet from commencing via the IsCancellationRequested property Existing executing iterations will run to their respective termination points Furthermore, calling Cancel() even after all iterations have completed will still cause the registered cancel event (via ctsTokenRegister()) to execute Also, the only means by which Parallel is able to acknowledge that the cancellation request has been processed (versus completed successfully) is via the OperationCanceledException Given that cancellation in this example is an option for the user, the exception is caught and ignored, allowing the application to display Canceling followed by a line of stars before exiting
Bar Code Encoder In VS .NET
Using Barcode generation for ASP.NET Control to generate, create bar code image in ASP.NET applications.
ADVANCED TOPIC Parallel Results and Options Although uncommon, it is possible to control the maximum degree of parallelism via the ParallelOptions parameter on overloads of both the ParallelFor() and ParallelForEach<T>() loops Although Microsoft has invested significantly across a wide range of processor counts, to
Barcode Maker In VB.NET
Using Barcode generation for VS .NET Control to generate, create bar code image in .NET applications.
18: Multithreading
GTIN - 12 Printer In VS .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create UPC Code image in Visual Studio .NET applications.
determine optimal numbers for the degree of parallelism at least in the general case there are specific cases where the developer knows more about the specific algorithm or circumstance such that changing the maximum degree of parallelism makes sense Circumstances include:
UPC A Printer In Java
Using Barcode creator for Java Control to generate, create UPC Symbol image in Java applications.
Setting the value to 1 This can be a means of turning off parallelism in
order to simplify debugging
Knowing that the algorithm doesn t scale beyond a certain upper
bound for example, if the algorithm is limited by additional hardware constraints such as the number of USB ports that are available
If the body of the iteration is blocked for long periods, and creating
additional parallel iterations (possibly also with extended blocking) will not increase the throughput and instead will cause unnecessary context switching with little to no progress To control the maximum degree of parallel, use the ParallelOptionsMaxDegreeOfParallelism property Additional settings available on an instance of ParallelOptions include a specific task scheduler (ParallelOptionsTaskScheduler) and the cancellation token (ParallelOptionsCancellationToken) The task scheduler has complete control over a Task s execution, including when, in what sequence, and on what thread a task executes For example, if a user repeatedly clicks Next to proceed to the next screen and all of the screens are loaded asynchronously you may want to execute iterations that load the data in last in, first out (LIFO) order because the user perhaps only wants to see the last screen he requested Alternatively, if the save operation occurs multiple times, again asynchronously, you probably want to enter the save requests in first in, first out (FIFO) order to avoid any overwriting of later changes The task scheduler provides a means of specifying how the tasks will execute in relation to each other The CancellationToken provides a mechanism to communicate to the loop that no further iterations should start Additionally, the body of an iteration can watch the cancellation token to determine if an early exit from the iteration is in order Like a standard for loop, Parallel s loops also support the concept of breaking to exit the loop and canceling any further