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| author | tromey <tromey@138bc75d-0d04-0410-961f-82ee72b054a4> | 2007-01-09 19:58:05 +0000 |
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| committer | tromey <tromey@138bc75d-0d04-0410-961f-82ee72b054a4> | 2007-01-09 19:58:05 +0000 |
| commit | 65bf3316cf384588453604be6b4f0ed3751a8b0f (patch) | |
| tree | 996a5f57d4a68c53473382e45cb22f574cb3e4db /libjava/classpath/external/jsr166/java/util/concurrent/package.html | |
| parent | 8fc56618a84446beccd45b80381cdfe0e94050df (diff) | |
| download | ppe42-gcc-65bf3316cf384588453604be6b4f0ed3751a8b0f.tar.gz ppe42-gcc-65bf3316cf384588453604be6b4f0ed3751a8b0f.zip | |
Merged gcj-eclipse branch to trunk.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@120621 138bc75d-0d04-0410-961f-82ee72b054a4
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| -rw-r--r-- | libjava/classpath/external/jsr166/java/util/concurrent/package.html | 222 |
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diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/package.html b/libjava/classpath/external/jsr166/java/util/concurrent/package.html new file mode 100644 index 00000000000..20227e1fece --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/package.html @@ -0,0 +1,222 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> +<html> <head> +<title>Concurrency Utilities</title> +</head> + +<body> + +<p> Utility classes commonly useful in concurrent programming. This +package includes a few small standardized extensible frameworks, as +well as some classes that provide useful functionality and are +otherwise tedious or difficult to implement. Here are brief +descriptions of the main components. See also the <tt>locks</tt> and +<tt>atomic</tt> packages. + +<h2>Executors</h2> + +<b>Interfaces.</b> {@link java.util.concurrent.Executor} is a simple +standardized interface for defining custom thread-like subsystems, +including thread pools, asynchronous IO, and lightweight task +frameworks. Depending on which concrete Executor class is being used, +tasks may execute in a newly created thread, an existing +task-execution thread, or the thread calling <tt>execute()</tt>, and +may execute sequentially or concurrently. {@link +java.util.concurrent.ExecutorService} provides a more complete +asynchronous task execution framework. An ExecutorService manages +queuing and scheduling of tasks, and allows controlled shutdown. The +{@link java.util.concurrent.ScheduledExecutorService} subinterface +and associated interfaces add support for delayed and periodic task execution. +ExecutorServices provide methods arranging asynchronous execution of +any function expressed as {@link java.util.concurrent.Callable}, the +result-bearing analog of {@link java.lang.Runnable}. A {@link +java.util.concurrent.Future} returns the results of a function, allows +determination of whether execution has completed, and provides a means to +cancel execution. A {@link java.util.concurrent.RunnableFuture} is +a Future that possesses a <tt>run</tt> method that upon execution, +sets its results. + +<p> + +<b>Implementations.</b> Classes {@link +java.util.concurrent.ThreadPoolExecutor} and {@link +java.util.concurrent.ScheduledThreadPoolExecutor} provide tunable, +flexible thread pools. The {@link java.util.concurrent.Executors} +class provides factory methods for the most common kinds and +configurations of Executors, as well as a few utility methods for +using them. Other utilities based on Executors include the concrete +class {@link java.util.concurrent.FutureTask} providing a common +extensible implementation of Futures, and {@link +java.util.concurrent.ExecutorCompletionService}, that assists in +coordinating the processing of groups of asynchronous tasks. + +<h2>Queues</h2> + +The java.util.concurrent {@link +java.util.concurrent.ConcurrentLinkedQueue} class supplies an +efficient scalable thread-safe non-blocking FIFO queue. Five +implementations in java.util.concurrent support the extended {@link +java.util.concurrent.BlockingQueue} interface, that defines blocking +versions of put and take: {@link +java.util.concurrent.LinkedBlockingQueue}, {@link +java.util.concurrent.ArrayBlockingQueue}, {@link +java.util.concurrent.SynchronousQueue}, {@link +java.util.concurrent.PriorityBlockingQueue}, and {@link +java.util.concurrent.DelayQueue}. The different classes cover the most +common usage contexts for producer-consumer, messaging, parallel +tasking, and related concurrent designs. The {@link +java.util.concurrent.BlockingDeque} interface extends +<tt>BlockingQueue</tt> to support both FIFO and LIFO (stack-based) +operations. Class {@link java.util.concurrent.LinkedBlockingDeque} +provides an implementation. + + +<h2>Timing</h2> + +The {@link java.util.concurrent.TimeUnit} class provides multiple +granularities (including nanoseconds) for specifying and controlling +time-out based operations. Most classes in the package contain +operations based on time-outs in addition to indefinite waits. In all +cases that time-outs are used, the time-out specifies the minimum time +that the method should wait before indicating that it +timed-out. Implementations make a "best effort" to detect +time-outs as soon as possible after they occur. However, an indefinite +amount of time may elapse between a time-out being detected and a +thread actually executing again after that time-out. All methods +that accept timeout parameters treat values less than or equal to +zero to mean not to wait at all. To wait "forever", you can use +a value of <tt>Long.MAX_VALUE</tt>. + +<h2>Synchronizers</h2> + +Four classes aid common special-purpose synchronization idioms. +{@link java.util.concurrent.Semaphore} is a classic concurrency tool. +{@link java.util.concurrent.CountDownLatch} is a very simple yet very +common utility for blocking until a given number of signals, events, +or conditions hold. A {@link java.util.concurrent.CyclicBarrier} is a +resettable multiway synchronization point useful in some styles of +parallel programming. An {@link java.util.concurrent.Exchanger} allows +two threads to exchange objects at a rendezvous point, and is useful +in several pipeline designs. + +<h2>Concurrent Collections</h2> + +Besides Queues, this package supplies Collection implementations +designed for use in multithreaded contexts: +{@link java.util.concurrent.ConcurrentHashMap}, +{@link java.util.concurrent.ConcurrentSkipListMap}, +{@link java.util.concurrent.ConcurrentSkipListSet}, +{@link java.util.concurrent.CopyOnWriteArrayList}, and +{@link java.util.concurrent.CopyOnWriteArraySet}. +When many threads are expected to access a given collection, +a <tt>ConcurrentHashMap</tt> is normally preferable to +a synchronized <tt>HashMap</tt>, and a +<tt>ConcurrentSkipListMap</tt> is normally preferable +to a synchronized <tt>TreeMap</tt>. A +<tt>CopyOnWriteArrayList</tt> is preferable to +a synchronized <tt>ArrayList</tt> when the expected number of reads +and traversals greatly outnumber the number of updates to a list. + +<p>The "Concurrent" prefix used with some classes in this package is a +shorthand indicating several differences from similar "synchronized" +classes. For example <tt>java.util.Hashtable</tt> and +<tt>Collections.synchronizedMap(new HashMap())</tt> are +synchronized. But {@link java.util.concurrent.ConcurrentHashMap} is +"concurrent". A concurrent collection is thread-safe, but not +governed by a single exclusion lock. In the particular case of +ConcurrentHashMap, it safely permits any number of concurrent reads as +well as a tunable number of concurrent writes. "Synchronized" classes +can be useful when you need to prevent all access to a collection via +a single lock, at the expense of poorer scalability. In other cases in +which multiple threads are expected to access a common collection, +"concurrent" versions are normally preferable. And unsynchronized +collections are preferable when either collections are unshared, or +are accessible only when holding other locks. + +<p> Most concurrent Collection implementations (including most Queues) +also differ from the usual java.util conventions in that their Iterators +provide <em>weakly consistent</em> rather than fast-fail traversal. A +weakly consistent iterator is thread-safe, but does not necessarily +freeze the collection while iterating, so it may (or may not) reflect +any updates since the iterator was created. + +<a name="MemoryVisibility"> +<h2> Memory Consistency Properties </h2> + +<a href="http://java.sun.com/docs/books/jls/third_edition/html/memory.html"> +Chapter 17 of the Java Language Specification</a> defines the +<i>happens-before</i> relation on memory operations such as reads and +writes of shared variables. The results of a write by one thread are +guaranteed to be visible to a read by another thread only if the write +operation <i>happens-before</i> the read operation. The +{@code synchronized} and {@code volatile} constructs, as well as the +{@code Thread.start()} and {@code Thread.join()} methods, can form +<i>happens-before</i> relationships. In particular: + +<ul> + <li>Each action in a thread <i>happens-before</i> every action in that + thread that comes later in the program's order. + + <li>An unlock ({@code synchronized} block or method exit) of a + monitor <i>happens-before</i> every subsequent lock ({@code synchronized} + block or method entry) of that same monitor. And because + the <i>happens-before</i> relation is transitive, all actions + of a thread prior to unlocking <i>happen-before</i> all actions + subsequent to any thread locking that monitor. + + <li>A write to a {@code volatile} field <i>happens-before</i> every + subsequent read of that same field. Writes and reads of + {@code volatile} fields have similar memory consistency effects + as entering and exiting monitors, but do <em>not</em> entail + mutual exclusion locking. + + <li>A call to {@code start} on a thread <i>happens-before</i> any action in the + started thread. + + <li>All actions in a thread <i>happen-before</i> any other thread + successfully returns from a {@code join} on that thread. + +</ul> + + +The methods of all classes in {@code java.util.concurrent} and its +subpackages extend these guarantees to higher-level +synchronization. In particular: + +<ul> + + <li>Actions in a thread prior to placing an object into any concurrent + collection <i>happen-before</i> actions subsequent to the access or + removal of that element from the collection in another thread. + + <li>Actions in a thread prior to the submission of a {@code Runnable} + to an {@code Executor} <i>happen-before</i> its execution begins. + Similarly for {@code Callables} submitted to an {@code ExecutorService}. + + <li>Actions taken by the asynchronous computation represented by a + {@code Future} <i>happen-before</i> actions subsequent to the + retrieval of the result via {@code Future.get()} in another thread. + + <li>Actions prior to "releasing" synchronizer methods such as + {@code Lock.unlock}, {@code Semaphore.release}, and + {@code CountDownLatch.countDown} <i>happen-before</i> actions + subsequent to a successful "acquiring" method such as + {@code Lock.lock}, {@code Semaphore.acquire}, + {@code Condition.await}, and {@code CountDownLatch.await} on the + same synchronizer object in another thread. + + <li>For each pair of threads that successfully exchange objects via + an {@code Exchanger}, actions prior to the {@code exchange()} + in each thread <i>happen-before</i> those subsequent to the + corresponding {@code exchange()} in another thread. + + <li>Actions prior to calling {@code CyclicBarrier.await} + <i>happen-before</i> actions performed by the barrier action, and + actions performed by the barrier action <i>happen-before</i> actions + subsequent to a successful return from the corresponding {@code await} + in other threads. + +</ul> + +@since 1.5 + +</body> </html> |
