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java.util.Collections will be introduced into java.util. Also, |
java.util.Collections will be introduced into java.util. Also, |
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although it is at the borders of being in scope of JSR-166, |
although it is at the borders of being in scope of JSR-166, |
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java.util.LinkedList will be adapted to support Queue, and |
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. |
a new non-thread-safe java.util.PriorityQueue will be added. |
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<p> Five implementations in java.util.concurrent support the extended |
<p> Five implementations in java.util.concurrent support the extended |
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BlockingQueue interface, that defines blocking versions of put and |
BlockingQueue interface, that defines blocking versions of put and |
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calling threads that compute functions returning results, via |
calling threads that compute functions returning results, via |
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Futures. This is supported in part by defining interface Callable, the |
Futures. This is supported in part by defining interface Callable, the |
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argument/result analog of Runnable. |
argument/result analog of Runnable. |
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<p> Executors provide a framework for executing Runnables. The |
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Executor manages queueing and scheduling of tasks, and creation and |
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teardown of threads. Depending on which concrete Executor class is |
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being used, tasks may execute in a newly created thread, an existing |
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task-execution thread, or the thread calling execute(), and may |
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execute sequentially or concurrently. |
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<p> Several concrete implementations of Executor are included in |
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java.util.concurrent, including ThreadPoolExecutor, a flexible thread |
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pool and ScheduledExecutor, which adds support for delayed and |
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periodic task execution. Executor can be used in conjunction with |
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FutureTask (which implements Runnable) to asynchronously start a |
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potentially long-running computation and query the FutureTask to |
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determine if its execution has completed. |
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<p> The <tt>Executors</tt> class provides factory methods for all |
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of the types of executors provided in |
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<tt>java.util.concurrent</tt>. |
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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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<h2>Locks</h2> |
<h2>Locks</h2> |
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The Lock interface supports locking disciplines that differ in |
The Lock interface supports locking disciplines that differ in |
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semantics (reentrant, semaphore-based, etc), and that can be used in |
semantics (reentrant, fair, etc), and that can be used in |
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non-block-structured contexts including hand-over-hand and lock |
non-block-structured contexts including hand-over-hand and lock |
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reordering algorithms. This flexibility comes at the price of more |
reordering algorithms. This flexibility comes at the price of more |
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awkward syntax. Implementations include Semaphore, ReentrantMutex |
awkward syntax. Implementations include ReentrantLock and |
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FIFOSemaphore, and CountDownLatch. |
FairReentrantLock. |
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<p> |
<p> |
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The Locks class additionally supports trylock-designs using builtin |
The Locks class additionally supports trylock-designs using builtin |
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people can make the mistake of calling cond.notify instead of |
people can make the mistake of calling cond.notify instead of |
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cond.signal. However, they will get IllegalMonitorState exceptions if |
cond.signal. However, they will get IllegalMonitorState exceptions if |
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they do, so they can detect the error if they ever run the code. |
they do, so they can detect the error if they ever run the code. |
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<p> |
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The implementation requires VM magic to atomically suspend and release |
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lock. But it is unlikely to be very challenging for JVM providers, |
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since most layer Java monitors on top of posix condvars or similar |
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low-level functionality anyway. |
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<h2>Atomic variables</h2> |
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Classes AtomicInteger, AtomicLong, AtomicDouble, AtomicFloat, and |
<h2>Atomic variables</h2> |
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AtomicReference provide simple scalar variables supporting |
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compareAndSwap (CAS) and related atomic operations. These are |
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desparately needed by those performing low-level concurrent system |
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programming, but much less commonly useful in higher-level frameworks. |
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The atomic subpackage includes a small library of classes, including |
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AtomicInteger, AtomicLong, and AtomicReference that support variables |
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performinf compareAndSet (CAS) and related atomic operations. |
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<h2>Timing</h2> |
<h2>Timing</h2> |
167 |
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|
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Java has always supported sub-millisecond versions of several native |
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 |
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 |
actually perform timing in finer-grained units. We address this by |
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introducing class Clock, which provides multiple granularities for |
introducing class TimeUnit, which provides multiple granularities for |
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both accessing time and performing time-out based operations. |
both accessing time and performing time-out based operations. |
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<h2>Synchronizers</h2> |
<h2>Synchronizers</h2> |
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Five classes aid common special-purpose synchronization idioms. |
Five classes aid common special-purpose synchronization idioms. |
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Semaphores and FifoSemaphores are classic concurrency tools. Latches |
Semaphores and FairSemaphores are classic concurrency tools. |
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are very simple yet very common objects useful for blocking until a |
CountDownLatches are very simple yet very common objects useful for |
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single signal, event, or condition holds. CyclicBarriers are |
blocking until a single signal, event, or condition holds. |
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resettable multiway synchronization points very common in some styles |
CyclicBarriers are resettable multiway synchronization points very |
182 |
of parallel programming. Exchangers allow two threads to exchange |
common in some styles of parallel programming. Exchangers allow two |
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objects at a rendezvous point. |
threads to exchange objects at a rendezvous point. |
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185 |
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186 |
<h2>Concurrent Collections</h2> |
<h2>Concurrent Collections</h2> |
187 |
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|
188 |
JSR 166 will supply a few Collection implementations designed for use |
JSR 166 will supply a few Collection implementations designed for use |
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in multithreaded contexts: ConcurrentHashTable, CopyOnWriteArrayList, |
in multithreaded contexts: ConcurrentHashMap, CopyOnWriteArrayList, |
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and CopyOnWriteArraySet. |
and CopyOnWriteArraySet. |
191 |
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192 |
<h2>Uncaught Exception Handlers</h2> |
<h2>Uncaught Exception Handlers</h2> |
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too inflexible in many multithreaded programs. (Note that the combination |
too inflexible in many multithreaded programs. (Note that the combination |
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of features in JSR 166 make ThreadGroups even less likely to |
of features in JSR 166 make ThreadGroups even less likely to |
199 |
be used in most programs. Perhaps they will eventually be deprecated.) |
be used in most programs. Perhaps they will eventually be deprecated.) |
200 |
<p> |
|
201 |
Additionally, ThreadLocals will now support a means to |
<p> Additionally, ThreadLocals will now support a means to remove a |
202 |
remove a ThreadLocals, which is needed in some thread-pool and |
ThreadLocal, which is needed in some thread-pool and worker-thread |
203 |
worker-thread designs. |
designs. |
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205 |
<hr> |
<hr> |
206 |
<address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address> |
<address><A HREF="http://gee.cs.oswego.edu/dl">Doug Lea</A></address> |