From Newsgroup: rec.sport.rowing

<div>Right now I am not understanding the differences between class level, object level, explicit and intrinsic locking in Java. Can someone please let me know which is what? Also, if I can get some examples to understand, that will be very helpful for me.</div><div></div><div></div><div></div><div></div><div></div><div>file lock java app download</div><div></div><div>Download Zip: https://t.co/rDCmTUtYq2 </div><div></div><div></div><div>An explicit lock is provided in Java 5+ in the package java.util.concurrent.locks. The most commonly used class is probably ReentrantLock. These provide alternatives to using the intrinsic locks and offer features that are not possible with intrinsic locks.</div><div></div><div></div><div>This distinction applies to intrinsic locks only. If you have a synchronized static method, the intrinsic lock used will be associated with the class object itself. If you synchronize on an object instance (or have a synchronized instance method) it will be an object-level lock.</div><div></div><div></div><div>When you use "Synchronized" keyword, it uses intrinsic locks or monitors. Every object in Java has an intrinsic lock associated with it. Whenever a thread tries to access a synchronized block or method, it acquires the intrinsic lock or the monitor on that object or Object level Lock. In case of static methods, the thread acquires the lock over the class object.</div><div></div><div></div><div>Biased locking is an optimization technique used in the HotSpot Virtual Machine to reduce the overhead of uncontended locking. It aims to avoid executing a compare-and-swap atomic operation when acquiring a monitor by assuming that a monitor remains owned by a given thread until a different thread tries to acquire it. The initial lock of the monitor biases the monitor towards that thread, avoiding the need for atomic instructions in subsequent synchronized operations on the same object. When many threads perform many synchronized operations on objects used in a single-threaded fashion, biasing the locks has historically led to significant performance improvements over regular locking techniques.</div><div></div><div></div><div></div><div></div><div></div><div></div><div>The performance gains seen in the past are far less evident today. Many applications that benefited from biased locking are older, legacy applications that use the early Java collection APIs, which synchronize on every access (e.g., Hashtable and Vector). Newer applications generally use the non-synchronized collections (e.g., HashMap and ArrayList), introduced in Java 1.2 for single-threaded scenarios, or the even more-performant concurrent data structures, introduced in Java 5, for multi-threaded scenarios. This means that applications that benefit from biased locking due to unnecessary synchronization will likely see a performance improvement if the code is updated to use these newer classes. Furthermore, applications built around a thread-pool queue and worker threads generally perform better with biased locking disabled. (SPECjbb2015 was designed that way, e.g., while SPECjvm98 and SPECjbb2005 were not). Biased locking comes with the cost of requiring an expensive revocation operation in case of contention. Applications that benefit from it are therefore only those that exhibit significant amounts of uncontended synchronized operations, like those mentioned above, so that the cost of executing cheap lock owner checks plus an occasional expensive revocation is still lower than the cost of executing the eluded compare-and-swap atomic instructions. Changes in the cost of atomic instructions since the introduction of biased locking into HotSpot also change the amount of uncontended operations needed for that relation to remain true. Another aspect worth noting is that applications won't have noticeable performance improvements from biased locking even when the previous cost relation is true when the time spend on synchronized operations is still only a small fraction of the total application workload.</div><div></div><div></div><div>Biased locking introduced a lot of complex code into the synchronization subsystem and is invasive to other HotSpot components as well. This complexity is a barrier to understanding various parts of the code and an impediment to making significant design changes within the synchronization subsystem. To that end we would like to disable, deprecate, and eventually remove support for biased locking.</div><div></div><div></div><div>Prior to JDK 15, biased locking is always enabled and available. With this JEP, biased locking will no longer be enabled when HotSpot is started unless -XX:+UseBiasedLocking is set on the command line.</div><div></div><div></div><div>Some Java applications may see a performance regression with biased locking disabled. Allowing biased locking to be re-enabled on the command line helps to mitigate this and provides possible insight into which situations may still benefit from its usage.</div><div></div><div></div><div>After reading other threads on similar issues, I made sure to give permissions to the node.lock file as well and also did a full restart of the machine to make sure nothing was lingering. (saw some other threads that there were issues with processes being hung up in the background, which is not the case here)</div><div></div><div></div><div>The guarantee provided by this class is that equal keys lead to the same lock (or semaphore), i.e. if (key1.equals(key2)) then striped.get(key1) == striped.get(key2) (assuming Object.hashCode() is correctly implemented for the keys). Note that if key1 is not equal to key2, it is not guaranteed that striped.get(key1) != striped.get(key2); the elements might nevertheless be mapped to the same lock. The lower the number of stripes, the higher the probability of this happening. There are three flavors of this class: Striped, Striped, and Striped. For each type, two implementations are offered: strong and weak Striped, strong and weak Striped, and strong and weak Striped. Strong means that all stripes (locks/semaphores) are initialized eagerly, and are not reclaimed unless Striped itself is reclaimable. Weak means that locks/semaphores are created lazily, and they are allowed to be reclaimed if nobody is holding on to them. This is useful, for example, if one wants to create a Striped of many locks, but worries that in most cases only a small portion of these would be in use. Prior to this class, one might be tempted to use Map, where K represents the task. This maximizes concurrency by having each unique key mapped to a unique lock, but also maximizes memory footprint. On the other extreme, one could use a single lock for all tasks, which minimizes memory footprint but also minimizes concurrency. Instead of choosing either of these extremes, Striped allows the user to trade between required concurrency and memory footprint. For example, if a set of tasks are CPU-bound, one could easily create a very compact Striped of availableProcessors() * 4 stripes, instead of possibly thousands of locks which could be created in a Map structure.Since: 13.0Author: Dimitris AndreouMethod SummaryMethods Modifier and TypeMethod and DescriptionIterablebulkGet(Iterable keys)Returns the stripes that correspond to the passed objects, in ascending (as per getAt(int)) order.abstract Lget(Object key)Returns the stripe that corresponds to the passed key.abstract LgetAt(int index)Returns the stripe at the specified index.static StripedlazyWeakLock(int stripes)Creates a Striped with lazily initialized, weakly referenced locks.static StripedlazyWeakReadWriteLock(int stripes)Creates a Striped with lazily initialized, weakly referenced read-write locks.static StripedlazyWeakSemaphore(int stripes, int permits)Creates a Striped with lazily initialized, weakly referenced semaphores, with the specified number of permits.static Stripedlock(int stripes)Creates a Striped with eagerly initialized, strongly referenced locks.static StripedreadWriteLock(int stripes)Creates a Striped with eagerly initialized, strongly referenced read-write locks.static Stripedsemaphore(int stripes, int permits)Creates a Striped with eagerly initialized, strongly referenced semaphores, with the specified number of permits.abstract intsize()Returns the total number of stripes in this instance.Methods inherited from class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitMethod Detailgetpublic abstract L get(Object key)Returns the stripe that corresponds to the passed key. It is always guaranteed that if key1.equals(key2), then get(key1) == get(key2).Parameters:key - an arbitrary, non-null keyReturns:the stripe that the passed key corresponds togetAtpublic abstract L getAt(int index)Returns the stripe at the specified index. Valid indexes are 0, inclusively, to size(), exclusively.Parameters:index - the index of the stripe to return; must be in [0...size())Returns:the stripe at the specified indexsizepublic abstract int size()Returns the total number of stripes in this instance.bulkGetpublic Iterable bulkGet(Iterable keys)Returns the stripes that correspond to the passed objects, in ascending (as per getAt(int)) order. Thus, threads that use the stripes in the order returned by this method are guaranteed to not deadlock each other. It should be noted that using a Striped with relatively few stripes, and bulkGet(keys) with a relative large number of keys can cause an excessive number of shared stripes (much like the birthday paradox, where much fewer than anticipated birthdays are needed for a pair of them to match). Please consider carefully the implications of the number of stripes, the intended concurrency level, and the typical number of keys used in a bulkGet(keys) operation. See Balls in Bins model for mathematical formulas that can be used to estimate the probability of collisions.Parameters:keys - arbitrary non-null keysReturns:the stripes corresponding to the objects (one per each object, derived by delegating to get(Object); may contain duplicates), in an increasing index order.lockpublic static Striped lock(int stripes)Creates a Striped with eagerly initialized, strongly referenced locks. Every lock is reentrant.Parameters:stripes - the minimum number of stripes (locks) requiredReturns:a new StripedlazyWeakLockpublic static Striped lazyWeakLock(int stripes)Creates a Striped with lazily initialized, weakly referenced locks. Every lock is reentrant.Parameters:stripes - the minimum number of stripes (locks) requiredReturns:a new Stripedsemaphorepublic static Striped semaphore(int stripes, int permits)Creates a Striped with eagerly initialized, strongly referenced semaphores, with the specified number of permits.Parameters:stripes - the minimum number of stripes (semaphores) requiredpermits - the number of permits in each semaphoreReturns:a new StripedlazyWeakSemaphorepublic static Striped lazyWeakSemaphore(int stripes, int permits)Creates a Striped with lazily initialized, weakly referenced semaphores, with the specified number of permits.Parameters:stripes - the minimum number of stripes (semaphores) requiredpermits - the number of permits in each semaphoreReturns:a new StripedreadWriteLockpublic static Striped readWriteLock(int stripes)Creates a Striped with eagerly initialized, strongly referenced read-write locks. Every lock is reentrant.Parameters:stripes - the minimum number of stripes (locks) requiredReturns:a new StripedlazyWeakReadWriteLockpublic static Striped lazyWeakReadWriteLock(int stripes)Creates a Striped with lazily initialized, weakly referenced read-write locks. Every lock is reentrant.Parameters:stripes - the minimum number of stripes (locks) requiredReturns:a new StripedOverviewPackageClassUseTreeDeprecatedIndexHelpPrev ClassNext ClassFramesNo FramesAll ClassesSummary: Nested Field Constr MethodDetail: Field Constr MethodCopyright 2010-2015. All Rights Reserved.</div><div></div><div> df19127ead</div>
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