Messaging through a service bus in .NET using MassTransit part 8: observing events in the bus

October 6, 2016 1 Comment

Introduction

In the previous post we learned how to intercept messages in MassTransit. We can intercept messages using various observer interfaces when sending, publishing, receiving and consuming messages. We cannot modify the message content so they are read-only operations. The implemented interfaces need to be registered with the bus so that we can do any extra work on the messages such as logging or debugging.

In this post we’ll see how to register events that happen in the bus.

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Generate truly random cryptographic keys using a random number generator in .NET

October 5, 2016 1 Comment

The well-known System.Random class lets us generate random numbers quickly. However, the values provided by System.Random are not truly random. Instead, they are pseudo-random. The return values should only be used in case true randomness is not that important, such as in the classic number-guessing game. In case you need a random value to be used in cryptography such as a cryptographic key in symmetric and asymmetric encryption then System.Random is not an acceptable option.

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Messaging through a service bus in .NET using MassTransit part 7: intercepting messages

October 4, 2016 5 Comments

Introduction

In the previous post we investigated how types are handled by MassTransit and how they are represented in RabbitMq exchanges and queues. With MassTransit we can send and receive concrete objects and it will take care of creating the necessary queues and exchanges for us. The objects are serialised and deserialised without us having to worry about JSON or XML strings.

In this post we’ll see how to intercept messages both in the publisher and receiver.

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Using immutable collections for thread-safe read-only operations in .NET

October 3, 2016 Leave a comment

Sometimes you have a scenario where multiple threads need to read from the same shared collection. We’ve looked at the 4 concurrent, i.e. thread-safe collection types on this blog that are available in the System.Collections.Concurrent namespace. They can be safely used for both concurrent writes and reads.

However, if your threads strictly only need to read from a collection then there’s another option. There are collections in the System.Collections.Immutable namespace that are immutable, i.e. read-only and have been optimisied for concurrent read operations.

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Sharing primitives across threads in Java using atomic objects

October 2, 2016 Leave a comment

Threading and parallel execution are popular choices when making applications more responsive and resource-efficient. Various tasks are carried out on separate threads where they either produce some result relevant to the main thread or just run in the background “unnoticed”. Often these tasks work autonomously meaning they have their own set of dependencies and variables. That is they do not interfere with a resource that is common to 2 or more threads.

However, that’s not always the case. Imagine that multiple threads are trying to update the same primitive like an integer counter. They perform some action and then update this counter. In this post we’ll see what can go wrong.

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Getting the result of the first completed parallel task in Java

October 1, 2016 Leave a comment

In this post we saw how to delegate one or more parallel tasks to different threads and wait for all of them to complete. We pretended that 4 different computations took 1,2,3 and respectively 4 seconds to complete. If we execute each calculation one after the other on the same thread then it takes 10 seconds to complete them all. We can do a lot better by assigning each operation to a separate thread and let them run in parallel. The Future and Callable of T objects along with a thread pool make this very easy to implement.

There are situations where we only need the result from 1 parallel operation. Imagine that it’s enough to complete 1 of the four computations in the example code so that our main thread can continue. We don’t know how long each operation will take so we let them have a race. The one that is executed first returns its value and the rest are interrupted and forgotten. We’ll see how to achieve that in this post.

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Performing some action while waiting for a key to be pressed in .NET console applications

September 30, 2016 Leave a comment

You can wait for the user to press some button in a .NET console application using the Console.ReadKey() method. That’s simple and easy to use, but occasionally you might want to perform some action while waiting for the user to press a key.

The KeyAvailable property of the Console object helps you achieve just that.

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Messaging through a service bus in .NET using MassTransit part 6: message types and inheritance support

September 29, 2016 1 Comment

Introduction

In the previous post we went through how exceptions are handled in MassTransit. By default the only mechanism is that if a registered consumer throws an exception while processing a message then that message ends up in an error queue. The error queue is named after the queue name where the consumer is listening with “_error” attached to it. By default MassTransit won’t try to relay the message again. However, it’s simple to add various retry policies with the UseRetry extension method. We can configure a wide range of retry policies: incremental, exponential, exception-based ones and other types. In addition MassTransit publishes a Fault message if all retries have been exhausted without success. The fault address or response address can specify a different queue where the fault message will be delivered. A different consumer can then monitor the fault queue and do something meaningful with the fault message.

In this post we’ll look at how message type inheritance is supported in MassTransit.

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Messaging through a service bus in .NET using MassTransit part 5: failures

September 28, 2016 Leave a comment

Introduction

In the previous post we explored how to inject a dependency into the registered consumer class in MassTransit. Consumer classes will often have at least some sort of dependency such as a repository interface or another abstraction to propagate the changes made. Good software engineering dictates that a class should indicate what dependencies it needs through e.g. its constructor. This is the contrary of control-freak objects that construct all their dependencies hidden in their implementations.

In this post we’ll take a look at various failure handling options in MassTransit.

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How to redirect standard output for a .NET console application

September 27, 2016 Leave a comment

Normally a .NET console application writes its messages directly to the console so that the user can view them. This is done with one of the “Write” methods like Console.WriteLine(some message) where you can prompt the user for some input.

However, this is not the only option you have. The standard output channel can be overridden.

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