Java Blocking Queue Multiple Consumers

Throttles can be implemented at the consumer side by limiting the number of concurrent consumers, or implement rate limiters or throttlers for either the producers or consumers. Connections exceeding the limitation of the queue will be dropped, but latencies for accepted connections become predictable. The problem describes two processes, the producer and the consumer, who share a common, fixed-size buffer used as a queue. Kafka source feature will be released in the syslog-ng GSoC version. • A sibling of message queue pattern but further generalizes it by delivering a message to multiple consumers – Message queue: delivers messages to only one receiver, i. Lock and semaphore, what's better method for my case. Similarly while. Java 9 has introduced some new interesting features in this old, yet very popular, programming language. The method call returns. Forgive me if any typo is there Sincerely, Hari. Creating a New Queue Instance As a best practice, it's recommended to use generic type and interface as reference type when creating a new collection. Beckman December 2008 1 Introduction In object-oriented programs, it is often the case that object types define usage protocols as an implicit part. This is necessary if we want to maintain throttling. Attaching thread dump,please let us know if we have any fix. A blocking queue is a queue that blocks when you try to dequeue from it and the queue is empty, or if you try to enqueue items to it and the queue is already Java Concurrency: Blocking Queues. Publish-Subscribe Systems. This problem can be easily solved using new BlockingQueue. In the first tutorial we wrote programs to send and receive messages from a named queue. Concurrent Pascal, Mesa, C#, and Java all implement monitors as described here. This event, hosted by No Fluff Just Stuff, is for alpha geek Java platform developers!. have a FIFO structure? Surprisingly, this is a \sloppy queue", which does not always respect the FIFO contract. The main. BlockingQueue implementations are designed to be used primarily for producer-consumer queues, but additionally support the Collection interface. Note that it doesn't block operations as done in the implementation of BlockingDequeue interface like LinkedBlockingDeque. One or more producers and one or more consumers might all be adding and removing items from the same queue. Notice: Undefined index: HTTP_REFERER in /srv/app842. Request processor queue load factor The API server parses requests and puts them in the executor queue. There is a difference between listener processes -- any of which can work on a request the same as the rest in parallel in separate threads or even on separate machines -- and having multiple different. Importantly, this means that producers and consumers can exist entirely without the presence of the other. Symptom ===== We have a network of 4 brokers that share messages using distributed queues via demand forwarding bridges. NET Fundamentals: Choosing the Right Collection Class. of consumers in group for a topic <=No. The thread that is waiting in the side room will wait there until it wakes up, at which point it will try to get back into the protected room. Path is an object that may be used to locate a file in a file system. Our JMS queue contains two kinds of XML messages - one conforming to schema1. Conversely, if the queue size is limited with a blocking queue, then HOL blocking problems can re-emerge as producers are prevented for queuing tasks that could be executed. In Java when you wait for the tasks you have to wait for "ALL" the tasks, and that's not efficient , and if you want to use the object from multiple threads i think it will have the same effect, you can avoid some of the problems by using many objects of the ThreadPoolExecutor class but this will take ressources and this will cause more and. Random"s nextInt call. Its architecture facilitates the creation of applications built from JavaBeans that exchange data asynchronously. Dec 20, 2016 · I think almost every project in the real world uses some form of producer-consumer queue. blocking queues and a cached thread pool. BlockingQueue tutorial. The requirement is that: If the queue is not full, all the producers should be able to produce products independently. Northern Virginia Software Symposium is April 25 - 27, 2014 in Reston, VA. In this post, I've tried to clear up the confusion around the subscribeOn and observeOn operators by showing a simplified, clutter free way of implementing them. Find out to manage the basic components of the Java Concurrency API. This example generates SimpleAddition objects that require an addition of two numbers to be performed on the consumer thread. Unfortunately,. Collections. Attaching thread dump,please let us know if we have any fix. Instead, it is being used to put multiple CPU cores on a single CPU die. This queue orders elements FIFO (first-in-first-out). A Queue is typically used as synchronizer. Similarly while. This document describes how to use the TPL Dataflow Library to implement a producer-consumer pattern. These are the top rated real world C++ (Cpp) examples of std::atomic::fetch_add extracted from open source projects. com The Producer-Consumer pattern implemented in Java; plus how to use the very handy ArrayBlockingQ. High availability / auto-failover to other consumers if a JVM goes down. This means a call to Take() will wait, potentially indefinitely, until there is something to return. That's all on How to use Blocking Queue to solve Producer Consumer problem or example of Producer consumer design pattern. In last article we have seen solving Producer Consumer problem in Java using blocking Queue but one of my reader emailed me and requested code example and explanation of solving Producer Consumer problem in Java with wait and notify method as well, Since its often asked as one. CON: The number of total threads across all processes will be limited by the total number of partitions. On one of my projects I needed to have a concurrent queue with multiple producers and multiple consumers. This event, hosted by No Fluff Just Stuff, is for alpha geek Java platform developers!. Consumer thread consumes integer from sharedQueue continuously. The tail of the queue is the element that has been on the queue the shortest time. In comparison to produce-consumer using wait notify this version using blocking queue is much simpler as you don't need to write the logic for making the thread wait or notifying the waiting thread. The Java runtime supports a scheduling algorithm known as fixed priority scheduling. The Reactor RabbitMQ API benefits from non-blocking back-pressure provided by Reactor. Because the queue works with blocks of elements, however, and not individual elements themselves, the value to pass in order to obtain an effective number of pre-allocated element slots is non-obvious. This setup guarantees that only one consumer processes a given message, no matter how many consumers there are. In the Consumer I give you an example how the wait() in Java can be used, and a possible way how to deal with InterruptedExcpetions. CountDownLatch, CyclicBarrier, and Callable and Future classes. In computer science, the readers-writers problems are examples of a common computing problem in concurrency. NET framework. Multi-threaded Dispatch in Java Client Recently I pushed branch bug18384 that changes the way callbacks are sent to Consumer implementations. The Consumer uses an Index to determine whether he should pull elements from the queue and increments the shouldRun after he has taken the 10 elements from the queue. public interface BlockingQueue extends Queue. We are running into the issue of having more items produced than I told it to produce. For example if i am having 25 messages in a particular queue. In general Kafka handles connections very efficiently so this is generally a small cost. When a blocking queue is used as synchronizer, consumers can wait for any arbitrary object to be available. A bounded collection that blocks Add and Take operations when the collection is full or empty. There are as many queues as there are unique hosts, but at any given time the total number of fetch. When a blocking queue is used as synchronizer, consumers can wait for any arbitrary object to be available. Producer(s) block until there is a consumer available; consumer(s) block until there is an enqueued message. Syslog-ng. New elements are inserted at the tail of the queue, and the queue. This document describes how to use the TPL Dataflow Library to implement a producer-consumer pattern. Finally we have to create BlockingQueue service for producer and consumer. Jun 16, 2015 · In this tutorial we will build a redis message queue. A blocking queue is a queue that blocks when you try to dequeue from it and the queue is empty, or if you try to enqueue items to it and the queue is already Java Concurrency: Blocking Queues. This arrangement occurs in many places within real systems. As with the standard Master/Slave pattern, the Producer/Consumer design consists of parallel loops which are broken down into two categories; producers, and consumers. 12/4: Whether to block any producer if the internal queue is full. In this case there is a producer that generates stuff to be consumed by the consumer, however the rate of production and the rate of consumption vary. In this article I wish to show a simple way to parallelize the consumers of a queue in memory. This had two main drawbacks. It may very well happen, that all producers and consumers of a given distributed datastructure (queue, topic, map) are on the same JVM or even in the same class-loader. Multiple threads or tasks can add items to the collection concurrently, and if the collection reaches its specified maximum capacity, the producing threads will block until an item is removed. how to solve consumer producer problem using wait() and notify() method in java. Attempts to put an element into a full queue will result in the operation blocking; attempts to take an element from an empty queue will similarly block. Its architecture facilitates the creation of applications built from JavaBeans that exchange data asynchronously. Redis can be used as a Message Queue. A simple producer/consumer queue. The notifyAll() method is actually used in most other cases. Kafka Tutorial: Writing a Kafka Consumer in Java. An optionally-bounded blocking queue based on linked nodes. We were validating the behaviour of the system when memory usage approached and exceeded the out-of-box memory limit (64MB). A Producer opens a file and puts the data into BlockingQueue. Returns the number of elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or Integer. This tutorial provides an introductory overview of the Java Message Service, its functionality, and its capabilities. This can be achieved by using a Blocking queue of fixed size. sendAdvisoryIfNoConsumers. Normally, active consumers connected to a queue receive messages from it in a round-robin fashion. If the queue is full, the producers have to wait. CON: Multiple consumers means more requests being sent to the server and slightly less batching of data which can cause some drop in I/O throughput. How To Create Your Own Non Blocking Fixed Size Queue In. This article includes a C# implementation of a Bound Blocking Queue (i. Before you go for the comparisons you need to learn the basics such as what is a JMS Queue what was the purpose of this technology and so on. The book is for Java developers and programmers at an intermediate to advanced level. The problem describes two processes, the producer and the consumer, who share a common, fixed-size buffer used as a queue. NET Fundamentals: Choosing the Right Collection Class. A dispatcher may also have a requirement for the mailbox type used by the actors running on it. In Java, the BlockingQueue interface is available in the java. An unbounded thread-safe queue based on linked nodes. It should be obvious that these functions are perfect for implementing an async producer/consumer queue. When you consume and ack your messages then producers will unblock. Another alternative is to have one or more consumer threads that do all data consumption and hands off ConsumerRecords instances to a blocking queue consumed by a pool of processor threads that actually handle the record processing. An example is the BalancingDispatcher which requires a message queue that is thread-safe for multiple concurrent consumers. So, for example, it is possible to remove an arbitrary element from a queue using remove(x). Please review and let me know if there is room for improvement. I'd like to see the API change so that even if WAIT FOREVER is specified (or any time limit really) AQ could raise ORA-25228 (no more messages waiting) to better manage the resources of the system. The Consumer and Supplier interfaces are a couple of Functional Interfaces that belong to the new Java 8 java. Asynchronous programming is a means of writing non-blocking code by running a task on a separate thread than the main application thread and notifying the main thread about its progress, completion or failure. It has an instruction pointer that keeps track of where within its context it is currently running. Condition interface provides method await and signal which work the same way as wait and notify. Note that a BlockingQueue can safely be used with multiple producers and multiple consumers. Asynchronous programming is a means of writing non-blocking code by running a task on a separate thread than the main application thread and notifying the main thread about its progress, completion or failure. Is this \queue" really a fair queue, i. The tail of the queue is the element that has been on the queue the shortest time. I ended up with a Scheduler -- N Producers -- M Consumers scheme, each two communicate via a queue (two queues total). If we are writing a new non-blocking service, we try to plan the metrics logging lifecycle up front, because it becomes very difficult to refactor and fix later on. It would be great if anyone could solve my crictical issue. Solve Consumer Producer problem by using wait() and notify() methods in multithreading solve Consumer Producer problem by using wait() and notify() methods, where consumer can consume only when production is over How to solve Consumer Producer problem without using wait() and notify() methods, where consumer can consume only when production is. Application needs to decouple consumers of some data from the logic that processes it. A BlockingQueue does not accept null elements. caveofprogramming. It was added on JDK with multiple concurrent utilities e. May 15, 2017 · Kafka Tutorial: Writing a Kafka Consumer in Java. BlockingQueue implementations are designed to be used primarily for producer-consumer queues with thread-safety. Java PriorityBlockingQueue is a concurrent collection and an implementation of BlockingQueue. Which Java blocking queue is most efficient for single-producer single-consumer scenarios. I'm using BlockingQueue for sharing common queue between multiple producers/consumers. ThreadMentor: The Producer/Consumer (or Bounded-Buffer) Problem. This means that no back pressure is given to the production of tasks and out of memory problems can result. In this BlockingQueue example we show how to write a very simple producer - consumer with a blocking queue. php(143) : runtime-created function(1) : eval()'d code(156) : runtime. What are the advantages of Blocking Queue in Java? A java. Throttles can be implemented at the consumer side by limiting the number of concurrent consumers, or implement rate limiters or throttlers for either the producers or consumers. The tail of the queue is that element that has been on the queue the shortest time. The PriorityBlockingQueue is an unbounded concurrent queue. See the diagram below. In fact there are multiple queues. Notice: Undefined index: HTTP_REFERER in /srv/app842. NET Base Class Library (BCL) has a wide array of collection classes at your disposal which make it easy to manage collections of objects. Another common anti-pattern is a single queue which has many consumers, each one with a distinct message selector. CON: More consumers means more TCP connections to the cluster (one per thread). The Java Message Service (JMS) API is a Java Message Oriented Middleware (MOM) API for sending messages between two or more clients. In this Java Tutorial we will go over same Producer/Consumer concept to explain the BlockingQueue in Java. where functions can be leveraged in ways not known before to simplify code and increase code modularity by using functional constructs like BiConsumers, Consumers, Predicates and Suppliers. The head of the queue is that element that has been on the queue the longest time. It has good support for asynchronous operations and can be used in. Add a dispatch queue class to the Android client. I am sure its much better than wait notify example but be prepare with both if you are going for any Java Interview as Interview may ask you both way. Simple, fast, and practical non-blocking and blocking concurrent queue algorithms Cache-aware lock-free queues for multiple producers/consumers and weak memory. Implement following interface so that multi-put is atomic. Jul 18, 2018 · In most cases, when a consumer encounters an empty queue, it has nothing to do and may as well block. Sid drops a table. *; import java. 10 Replies Latest reply on Apr 5, 2007 2:55 AM by 843789. Apr 03, 2014 · I thought this was clearly spelt out in the Java Client Doc, but I can only find this: Callbacks to Consumers are dispatched on a thread separate from the thread managed by the Connection. Providing you use the ticket ID as the routing key, this can ensure that all messages with the same routing key will end up on the same exchange. Tuning the queue size and timeout time together offers a lot of flexibility and a tradeoff between queuing performance vs. A "consumer" represents a logical entity of your architecture. Since the wait-notify mechanism is often integrated with the synchronisation mechanism (like in Java), it makes sense to incorporate blocking of the consumer into the queue mechanism itself. An example producer/consumer making use of a blocking queue implementation and executor framework is as follows:. Java Message Service. If you examine the behavior of System. What this means is that, while in traditional key-value stores you associated string keys to string values, in Redis the value is not limited to a simple string, but can also. Calls the consumer's Consumer. Cloudera delivers an Enterprise Data Cloud for any data, anywhere, from the Edge to AI. We should see PriorityBlockingQueue as a PriorityQueue with added operations for blocking retrieval. The requirement is that: If the queue is not full, all the producers should be able to produce products independently. the queue to become non-empty when retrieving an element; space to become available in the queue when storing an element. This queue must be safe for concurrency. You will send records with the Kafka producer. concurrent package represents a queue which is thread safe to put into, and take instances from. of consumers in group for a topic <=No. Consumer Groups - these are groups of consumers that are used to load share. This is a typical interview question: What is the difference between a Queue and a Topic ( or Queue Vs Topic). If the queue is not full, all the producers should be able to produce products independently. (The full set of ParallelExtensionsExtras Tour posts is available here. Blocking queue: Achieved using. So, your 2nd option wont work for us, and option 1 seems to be the only way to go. This tutorial covers advanced producer topics like custom serializers, ProducerInterceptors, custom Partitioners, timeout, record batching & linger, and compression. Kafka source can be used for queue Syslog-ng instances with Kafka. The main. NET Fundamentals: Choosing the Right Collection Class. Kafka Tutorial 14: Creating Advanced Kafka Consumers in Java Slides. Rather than spreading on a per message basis, consumers read from different partitions. Thus the producer will wait for the consumers to consume some items when the queue capacity is full. Collection interface. A new constructor, java. BlockingQueue implementations are designed to be used primarily for producer-consumer queues. Nov 26, 2017 · A ConcurrentLinkedDeque in Java is an appropriate choice when many threads share access to a common collection as concurrent insertion, removal, and access operations execute safely across multiple threads. If you want to consume concurrently from a queue, then you must use a different session for each consumer. It uses the same ordering rules as the java. The Reactor RabbitMQ API benefits from non-blocking back-pressure provided by Reactor. Novixys Software Dev Blog. This tutorial covers advanced producer topics like custom serializers, ProducerInterceptors, custom Partitioners, timeout, record batching & linger, and compression. Controller Accepts input and converts it to commands for the model or view. Disruptor With Parallel Consumers Vs Multiple Worker. Some time. I have a stand alone enterprise java application (not an EJB) that currently runs on several servers (one application per server). When QueueingConsumer was introduced, callbacks to Consumers were made on the Connection's thread. When you have multiple producers and consumers, you can still use this queue with some external locking. You can also publish messages asynchronously using the Java client. Path is an object that may be used to locate a file in a file system. This article includes a C# implementation of a Bound Blocking Queue (i. Strictly, it is required to notify. You can rate examples to help us improve the quality of examples. Collections. 1 Producer – A Runnable object to. He is the author of the books, Java 7 Concurrency Cookbook and Mastering Concurrency Programming with Java 8 by Packt Publishing. Given a large number of data types you want to ensure the consumers are from a pool of worker threads that consumed the far larger number of queues of data types. This queue orders elements FIFO (first-in-first-out). Producer-Consumer program in Java Using ArrayBlockingQueue. In this thread concurrency tutorial we will learn how to Solve Consumer Producer problem by using BlockingQueue and LinkedBlockingQueue in multithreading in java using example and program. Method from java. This tutorial demonstrates how to process records from a Kafka topic with a Kafka Consumer. queue/declare returns to you. This method call enables a fast and efficient way to create new threads in both Linux and Windows. I am sure its much better than wait notify example but be prepare with both if you are going for any Java Interview as Interview may ask you both way. Not only is it possible, it is desirable to have multiple listeners for a queue. The JavaDoc says: BlockingQueue is “A Queue that additionally supports operations that wait for the queue to become non-empty when retrieving an element, and wait for space to become available in the queue when storing an element. A dispatcher may also have a requirement for the mailbox type used by the actors running on it. This is equivalent to calling buildStream(source). A pool of threads polls the queue for incoming requests, and then process and respond. The active object computing model combines multiple traditional event loops with a multitasking environment. Sep 30, 2010 · A queue sender activity sends messages into the specified queue. A blocking queue is an implementation of one of the classic patterns in parallel processing: the producer/consumer pattern. For example if i am having 25 messages in a particular queue. PriorityQueue class. Oracle’s Java SE offerings are constantly evolving to better address the need of our users. CON: More consumers means more TCP connections to the cluster (one per thread). Usage example, based on a typical producer-consumer scenario. Related Articles:. The goal is to process messages concurrently from a queue in an asynchronous listener's onMessage method by attaching a listener instance to multiple consumer's with each consumer using its own session and running in a separate thread, that way the messages are passed on to the different consumers for concurrent processing. Often also called a replicated workers or worker-crew model, a thread pool maintains multiple threads waiting for tasks to be allocated for concurrent execution by the supervising program. But that introduces other problems. If your request gets stuck behind a slow request then your response time will suffer. If the queue is not full, all the producers should be able to produce products independently. If the queue is not empty, the consumer can consume products independently. That’s all on How to use Blocking Queue to solve Producer Consumer problem or example of Producer consumer design pattern. That's all on How to use Blocking Queue to solve Producer Consumer problem or example of Producer consumer design pattern. We will see a producer consumer based example using ArrayBlockingQueue to understand the BlockingQueue interface. public interface BlockingQueue extends Queue. when there are multiple producers with a single consumer as in my football match. A simple BlockingQueue example, a producer generates data and put it into a queue, at the same time, a consumer takes the data from the same queue. BlockingQueue tutorial. 9 Synchronization Examples ( Optional ) This section looks at how synchronization is handled in a number of different systems. In general, this is a queue that has a fixed number of elements it can contain (i. , bounded), and will "block" a producer if queue is full, or block a consumer if queue is empty. This is the basic implementation of thread safe producer consumer design pattern using Blocking queue. I'd like to see the API change so that even if WAIT FOREVER is specified (or any time limit really) AQ could raise ORA-25228 (no more messages waiting) to better manage the resources of the system. Single-consumer (sc) or Multiple-consumer (mc) denote the equivalent for the removal of data from the data structure. This is a classic "bounded buffer", in which a fixed-sized array holds elements inserted by producers and extracted by consumers. CON: More consumers means more TCP connections to the cluster (one per thread). This triggers the creation of a method request, which. Java Producer and Consumer Implementation using Blocking Queue 'Java Consumer Producer' example - This is one of frequently asked questions to senior core java developer. There are multiple queue classes in the java. A new entry would wake up a worker which would acquire the right to work the given queue. This queue orders elements FIFO (first-in-first-out). Common example of. There are two groups of threads, producers and consumers. 800+ Java interview questions answered with lots of diagrams, code and tutorials for entry level to advanced job interviews. Java concurrency producer and consumer solution is demonstrated below. If the queue is not full, all the producers should be able to produce products independently. Finally, Program. Play Framework makes it easy to build web applications with Java & Scala. Can have "consumer groups" -- multiple consumers nodes consuming a stream, where each message is processed by one node. Blocking Queue solves much of the problem of synchronization mechanism handled by wait() and notify() in producer-consumer problem. The work queue is a FIFO data structure that has only two operations: push() and pop(). This tutorial covers advanced producer topics like custom serializers, ProducerInterceptors, custom Partitioners, timeout, record batching & linger, and compression. Java Classic Producer and Consumer with Blocking Queue example Posted on January 20, 2013 by newjavablogger 'Java Consumer Producer' example - This is one of frequently asked questions to senior core java developer. Normally, active consumers connected to a queue receive messages from it in a round-robin fashion. How to: Implement a Producer-Consumer Dataflow Pattern. As with the standard Master/Slave pattern, the Producer/Consumer design consists of parallel loops which are broken down into two categories; producers, and consumers. I ended up with a Scheduler -- N Producers -- M Consumers scheme, each two communicate via a queue (two queues total). Producer and Consumer then producer thread can communicate to the consumer that it can start consuming now because there are items to consume in the queue. A queue-based fetcher. Close() method this is called when all Producers threads complete adding items to Queue so that consumer will know when to stop or cancel the Enumeration. All rights reserved. The requirement is that: If the queue is not full, all the producers should be able to produce products independently. Any representation of information such as a chart, diagram or table. Producer Consumer Pattern using BlockingQueue Java provides a built-in blocking queue data structure in java. In Java, the BlockingQueue interface is available in the java. To get semantics similar to a queue in a traditional messaging system all processes would be part of a single consumer group and hence record delivery would be balanced over the group like with a queue. Java Message Service. If the queue is not full, all the producers should be able to produce products independently. Thus the producer will wait for the consumers to consume some items when the queue capacity is full. BlockingQueue implementations are designed to be used primarily for producer-consumer queues. The Alerts will now pile up in this queue until someone actually consumes them and sends out the Alerts notifications to the users. , the bounded buffer); a thread pool of consumers each take a request out of the work queue and process the. Here's a closer look at the different scenarios using a fictive example of an ordering system with multiple consumers interested in messages when new orders are created: Registering a consumer Figure 1: Registering a consumer to a queue. As soon as, an element is taken from queue, it adds the element to queue. Deref'ing blocks until acknowledgement occurs, or throws an exception if something in the network or Riemann went wrong. 4: The queue size for the internal hand-off queue between the polling consumer, and producers sending data into the queue. Requiring a Message Queue Type for a Dispatcher. The Object class in java contains three final methods that allows threads to communicate about the lock status of a resource. This depends if. Properties of Non-Blocking Data Structures. This document describes how to use the TPL Dataflow Library to implement a producer-consumer pattern. All using the same shared reply queue. java will take a file, producer. With async send, the producer will put the message in a blocking queue and return immediately. We are defining the file store. async is to decouple producers and consumers of information in software, without dictating specific thread or blocking semantics, and without introducing callback hell. Tuning the queue size and timeout time together offers a lot of flexibility and a tradeoff between queuing performance vs. Each consumer will take an element from a BlockingQueue using take() method so it will block until there is an element in a queue. I had to use a multi-threaded producer and a multi-threaded consumer. java will take a file, producer. Remove all; Build the simple Non Blocking API This play list has the list of videos that will explain you the Java 8 features such as Lambdas, Streams. Queue and System. php(143) : runtime-created function(1) : eval()'d code(156) : runtime. blocking queues and a cached thread pool. Simpler Concurrent & Distributed Systems Actors and Streams let you build systems that scale up , using the resources of a server more efficiently, and out , using multiple servers. I have a producer placing stuff in a blocking queue, and a single consumer later picki…. Normally, active consumers connected to a queue receive messages from it in a round-robin fashion. Condition interface provides method await and signal which work the same way as wait and notify. *; import java. As mentioned in this post by Alex Miller TransferQueue is more generic and useful than SynchronousQueue however as it allows you to flexibly decide whether to use normal BlockingQueue semantics or a guaranteed hand-off. NET Fundamentals: Choosing the Right Collection Class. Add the import statements for the common Java and Android classes. That is, essentially, a data structure with several tails but one head, that allows a reader, crucially, to block on more. The Blocking Consumer. jobs from Tech Jobs North East.