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<A HREF="http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest"> http://altair.cs.oswego.edu/mailman/listinfo/concurrency-interest</A> . |
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<p> |
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<em> |
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Disclaimer - This prototype is experimental code developed as part of |
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JSR166 and made available to the developer community for use |
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as-is. It is not a supported product. Use it at your own risk. The |
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specification, language and implementation are subject to change as a |
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result of your feedback. Because these features have not yet been |
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approved for addition to the Java language, there is no schedule for |
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their inclusion in a product. |
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</em> |
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<p> |
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Package java.util.concurrent contains utility classes that are |
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commonly useful in concurrent programming. Like package java.util, it |
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includes a few small standardized extensible frameworks, as well as |
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conservative in selecting only those APIs and implementations that are |
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useful enough to encourage nearly all concurrent programmers to use |
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routinely. JSR 166 also includes a few changes and additions in |
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packages outside of java.util.concurrent: java.lang, to address timing |
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and uncaught exceptions, and java.util to better integrate queues, and |
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to make Timers conform to new frameworks. The API covers: |
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packages outside of java.util.concurrent: java.lang, to address |
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uncaught exceptions, and java.util to better integrate queues. |
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The API covers: |
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|
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<ul> |
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<li> Queues |
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<li> Condition variables |
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<li> Atomic variables |
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<li> Timing |
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<li> Barriers |
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<li> Synchronizers |
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<li> Concurrent Collections |
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<li> Uncaught Exception Handlers |
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</ul> |
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java.util.LinkedList will be adapted to support Queue, and |
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a new non-thread-safe java.util.HeapPriorityQueue will be added. |
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<p> |
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Four implementations in java.util.concurrent support the extended |
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<p> Five implementations in java.util.concurrent support the extended |
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BlockingQueue interface, that defines blocking versions of put and |
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take: LinkedBlockingQueue, ArrayBlockingQueue, SynchronousQueue, and |
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PriorityBlockingQueue. Additionally, java.util.concurrent.LinkedQueue |
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supplies an efficient thread-safe non-blocking queue. |
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<p> |
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Since the target release is JDK1.5, and generics are slated to be in |
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1.5, Queues should be parametrized on element type. (Also some others |
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below.) We are ignoring this for now. |
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take: LinkedBlockingQueue, ArrayBlockingQueue, SynchronousQueue, |
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PriorityBlockingQueue, and DelayQueue. Additionally, |
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java.util.concurrent.LinkedQueue supplies an efficient thread-safe |
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non-blocking queue. |
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|
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<p> Since the target release is JDK1.5, and generics are slated to be |
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in 1.5, Queues are parametrized on element type. (Also some others |
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below.) |
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<h2>Executors</h2> |
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thread-like subsystems, including thread pools, asynch-IO, and |
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lightweight task frameworks. Executors also standardize ways of |
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calling threads that compute functions returning results, via |
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Futures. This is supported in part by defining java.lang.Callable, the |
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Futures. This is supported in part by defining interface Callable, the |
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argument/result analog of Runnable. |
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|
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<p> While the Executor framework is intended to be extensible (so |
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includes for example, AbstractExecutor that simplifies construction of |
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new implementations), the most commonly used Executor will be |
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ThreadExecutor, which can be configured to act as all sorts of thread |
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pools, background threads, etc. The class is designed to be general |
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enough to suffice for the vast majority of usages, even sophisticated |
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ones, yet also includes methods and functionality that simplify |
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routine usage. |
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|
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<p> |
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A few methods will also be added to the java.util.Timer to support |
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Futures, and address other requests for enhancement. |
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<p> While the Executor framework is intended to be extensible the most |
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commonly used Executor will be ThreadExecutor, which can be configured |
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to act as all sorts of thread pools, background threads, etc. The |
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class is designed to be general enough to suffice for the vast |
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majority of usages, even sophisticated ones, yet also includes methods |
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and functionality that simplify routine usage. |
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|
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<h2>Locks</h2> |
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|
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Java has always supported sub-millisecond versions of several native |
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time-out-based methods (such as Object.wait), but not methods to |
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actually perform timing in finer-grained units. We address this by |
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introducing java.lang.Clock, which provides multiple granularities for |
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introducing class Clock, which provides multiple granularities for |
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both accessing time and performing time-out based operations. |
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|
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<h2>Barriers</h2> |
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<h2>Synchronizers</h2> |
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|
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Barriers (multiway synchronization points) are very common in some |
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styles of parallel programming, yet tricky to get right. The two most |
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useful flavors (CyclicBarriers and Exchangers) don't have much of an |
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interface in common, and only have one standard implementation each, |
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so these are simply defined as public classes rather than interfaces |
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and implementations. |
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Five classes aid common special-purpose synchronization idioms. |
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Semaphores and FifoSemaphores are classic concurrency tools. Latches |
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are very simple yet very common objects useful for blocking until a |
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single signal, event, or condition holds. CyclicBarriers are |
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resettable multiway synchronization points very common in some styles |
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of parallel programming. Exchangers allow two threads to exchange |
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objects at a rendezvous point. |
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|
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|
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<h2>Concurrent Collections</h2> |
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|
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There are no new interfaces, but JSR 166 will supply a few Collection |
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implementations designed for use in multithreaded contexts: |
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ConcurrentHashTable, CopyOnWriteArrayList, and CopyOnWriteArraySet. |
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JSR 166 will supply a few Collection implementations designed for use |
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in multithreaded contexts: ConcurrentHashTable, CopyOnWriteArrayList, |
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and CopyOnWriteArraySet. |
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|
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<h2>Uncaught Exception Handlers</h2> |
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|
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of features in JSR 166 make ThreadGroups even less likely to |
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be used in most programs. Perhaps they will eventually be deprecated.) |
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<p> |
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Additionally, Threads and ThreadLocals will now support a means to |
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clear and remove ThreadLocals, which is needed in some thread-pool and |
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> |
Additionally, ThreadLocals will now support a means to |
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remove a ThreadLocals, which is needed in some thread-pool and |
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worker-thread designs. |
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|
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<hr> |
