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java.util.Collections will be introduced into java.util. Also, |
java.util.Collections will be introduced into java.util. Also, |
| 76 |
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, |
| 77 |
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 |
| 98 |
Futures. This is supported in part by defining interface Callable, the |
Futures. This is supported in part by defining interface Callable, the |
| 99 |
argument/result analog of Runnable. |
argument/result analog of Runnable. |
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<p> While the Executor framework is intended to be extensible the most |
<p> Executors provide a framework for executing Runnables. The |
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commonly used Executor will be ThreadExecutor, which can be configured |
Executor manages queueing and scheduling of tasks, and creation and |
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to act as all sorts of thread pools, background threads, etc. The |
teardown of threads. Depending on which concrete Executor class is |
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class is designed to be general enough to suffice for the vast |
being used, tasks may execute in a newly created thread, an existing |
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majority of usages, even sophisticated ones, yet also includes methods |
task-execution thread, or the thread calling execute(), and may |
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and functionality that simplify routine usage. |
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 |
| 112 |
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FutureTask (which implements Runnable) to asynchronously start a |
| 113 |
|
potentially long-running computation and query the FutureTask to |
| 114 |
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determine if its execution has completed. |
| 115 |
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| 116 |
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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>. |
| 119 |
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| 120 |
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|
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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 |
| 124 |
semantics (reentrant, semaphore-based, etc), and that can be used in |
semantics (reentrant, fair, etc), and that can be used in |
| 125 |
non-block-structured contexts including hand-over-hand and lock |
non-block-structured contexts including hand-over-hand and lock |
| 126 |
reordering algorithms. This flexibility comes at the price of more |
reordering algorithms. This flexibility comes at the price of more |
| 127 |
awkward syntax. Implementations include Semaphore, ReentrantMutex |
awkward syntax. Implementations include ReentrantLock and |
| 128 |
FIFOSemaphore, and CountDownLatch. |
FairReentrantLock. |
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|
| 130 |
<p> |
<p> |
| 131 |
The Locks class additionally supports trylock-designs using builtin |
The Locks class additionally supports trylock-designs using builtin |
| 155 |
people can make the mistake of calling cond.notify instead of |
people can make the mistake of calling cond.notify instead of |
| 156 |
cond.signal. However, they will get IllegalMonitorState exceptions if |
cond.signal. However, they will get IllegalMonitorState exceptions if |
| 157 |
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. |
|
<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, |
|
|
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> |
|
| 159 |
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|
| 160 |
Classes AtomicInteger, AtomicLong, AtomicDouble, AtomicFloat, and |
<h2>Atomic variables</h2> |
|
AtomicReference provide simple scalar variables supporting |
|
|
compareAndSwap (CAS) and related atomic operations. These are |
|
|
desparately needed by those performing low-level concurrent system |
|
|
programming, but much less commonly useful in higher-level frameworks. |
|
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| 162 |
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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 |
| 164 |
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performinf compareAndSet (CAS) and related atomic operations. |
| 165 |
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|
| 166 |
<h2>Timing</h2> |
<h2>Timing</h2> |
| 167 |
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|
| 168 |
Java has always supported sub-millisecond versions of several native |
Java has always supported sub-millisecond versions of several native |
| 169 |
time-out-based methods (such as Object.wait), but not methods to |
time-out-based methods (such as Object.wait), but not methods to |
| 170 |
actually perform timing in finer-grained units. We address this by |
actually perform timing in finer-grained units. We address this by |
| 171 |
introducing class Clock, which provides multiple granularities for |
introducing class TimeUnit, which provides multiple granularities for |
| 172 |
both accessing time and performing time-out based operations. |
both accessing time and performing time-out based operations. |
| 173 |
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| 174 |
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| 175 |
<h2>Synchronizers</h2> |
<h2>Synchronizers</h2> |
| 176 |
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|
| 177 |
Five classes aid common special-purpose synchronization idioms. |
Five classes aid common special-purpose synchronization idioms. |
| 178 |
Semaphores and FifoSemaphores are classic concurrency tools. Latches |
Semaphores and FairSemaphores are classic concurrency tools. |
| 179 |
are very simple yet very common objects useful for blocking until a |
CountDownLatches are very simple yet very common objects useful for |
| 180 |
single signal, event, or condition holds. CyclicBarriers are |
blocking until a single signal, event, or condition holds. |
| 181 |
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 |
| 183 |
objects at a rendezvous point. |
threads to exchange objects at a rendezvous point. |
| 184 |
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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, |
| 190 |
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 |
| 198 |
of features in JSR 166 make ThreadGroups even less likely to |
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.) |
be used in most programs. Perhaps they will eventually be deprecated.) |
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<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 |
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worker-thread designs. |
designs. |
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<hr> |
<hr> |
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<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> |
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