readwritelock

ReadWriteLock. Understanding upgrading from readLock to writeLock

由 岁酱吖の 提交于 2019-12-23 17:33:53
问题 Consider this JDK standard interface: public interface ReadWriteLock{ public Lock readLock(); public Lock writeLock(); } B. Goetz in Java Concurrency in practice mentioned upgrading from readLock to writeLock is deadlock-prone. If two readers simultaneously attempt to upgrade to a write lock, neither will realese the read lock. The thing that's confused me is that it was two readers attempting to upgrade. But even one reader is enough, isn't? If a reader tries to upgrade it's not released the

Java : ReentrantReadWriteLock with priority

由 一世执手 提交于 2019-12-19 02:54:28
问题 The following is the typical reader and writer pattern (a lot of reads and few writes) private ReadWriteLock lock = new ReentrantReadWriteLock(); private int value; public void writeValue(int newValue){ lock.writeLock().lock(); try{ this.value = newValue; } finally{ lock.writeLock().unlock(); } } public int readValue(){ lock.readLock().lock(); try{ return value; } finally{ lock.writeLock().unlock(); } } I am wondering that is it possible to have priority to writer and reader ? For example,

Java并发编程初级篇(十四)：使用读写所实现同步机制

由 蓝咒 提交于 2019-12-12 19:43:03
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> Java API除了提供Lock()接口之外，还为我们提供了一个读写锁接口ReadWriteLock，使用这个锁的实现类ReentrantReadWriteLock可以让我们把读锁和写锁进行分离，对同步数据进行修改的时候使用写锁，这时候其他需要获取写锁的线程会被挂起，同时使用读锁的线程也会被挂起。而读取数据的时候使用读锁，这时候使用读锁的线程可以并发访问，以提高效率。 public interface ReadWriteLock { /** * Returns the lock used for reading. * * @return the lock used for reading. */ Lock readLock(); /** * Returns the lock used for writing. * * @return the lock used for writing. */ Lock writeLock(); } 我们模拟一个修改价格的例子，来看一下读锁与写锁是如何使用的。 创建一个价格类，里面两个商品的价格以及一个读写锁。在修改价格的方法里我们使用写锁，在读取商品价格的方法里我们使用读锁。修改商品价方法休眠两秒来模拟修改价格的过程，并打印修改价格信息。 public class

What strategy to use in Java for hierarchical reentrant read/write locking?

由 痴心易碎 提交于 2019-12-08 17:24:31
问题 I'm looking for en efficient system to have a series of read/write locks organized hierarchically to manage access to hierarchically organized resources. If a subtree is locked for write, then no other lock should be able to be obtained in the whole subtree until it is released; similarly, a write lock in a subtree should prevent locking in a parent. Here are the ideas I was contemplating: Use the Apache Commons Transaction . Unforunately, the project hasn't been updated since March 2008 and

How to replace a concurrently instance without losing data?

由 丶灬走出姿态 提交于 2019-12-08 03:16:55
问题 I have many threads who save the state and one thread that logs the state. I'd like to not lose data, which means to always log the latest state. The solution I have is to use a read-write lock when replacing/clearing the stats collection, which will not loose data but looks very cumbersome. See code below. What I would like is some way to run some code atomically while an instance isn't changed. Needless to say that the instance change should be atomically as well. The cumbersome solution

Synchronized vs ReadWriteLock performance

由 左心房为你撑大大i 提交于 2019-12-07 07:30:43
问题 I try to prove that synchronized is slower when there are many readers and only some writers. Somehow I proved the opposite. The RW example, time of execution is 313 ms: package zad3readWriteLockPerformance; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; public class Main { public static long start, end; public

Synchronized vs ReadWriteLock performance

由 馋奶兔 提交于 2019-12-05 14:39:40
I try to prove that synchronized is slower when there are many readers and only some writers. Somehow I proved the opposite. The RW example, time of execution is 313 ms: package zad3readWriteLockPerformance; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; public class Main { public static long start, end; public static void main(String[] args) { Runtime.getRuntime().addShutdownHook(new Thread(() -> { end = System

using java FileChannel FileLock to prevent file writes but allow reads

由 牧云@^-^@ 提交于 2019-12-01 19:24:15
问题 I think I'm misunderstanding how the FileChannel's locking features work. I want to have an exclusive write lock on a file, but allow reads from any process. On a Windows 7 machine running Java 7, I can get FileChannel's lock to work, but it prevents both reads and writes from other processes. How can I achieve a file lock that disallows writes but allows reads by other processes? 回答1: FileChannel.lock() deals with file regions, not with the file itself. The lock can be either shared (many

How to implement a reader/writer lock in C++14

由 不想你离开。 提交于 2019-12-01 13:17:47
I have a hash table data structure that I wish to make thread safe by use of a reader/writer lock (my read:write ratio is likely somewhere in the region of 100:1). I have been looking around for how to implement this lock using C++11 ( such as the method here ), but it has come to my attention that it should be possible to use C++14's shared_lock to accomplish the same thing. However, after looking on cppreference I have found both std::shared_lock and std::unique_lock but I don't understand how to use them together (compared to the Boost way which has simple method calls for locking both

How to implement a reader/writer lock in C++14

由 假装没事ソ 提交于 2019-12-01 10:16:29
问题 I have a hash table data structure that I wish to make thread safe by use of a reader/writer lock (my read:write ratio is likely somewhere in the region of 100:1). I have been looking around for how to implement this lock using C++11 (such as the method here), but it has come to my attention that it should be possible to use C++14's shared_lock to accomplish the same thing. However, after looking on cppreference I have found both std::shared_lock and std::unique_lock but I don't understand
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