synchronized

How to obtain a customized synchronizedList in java?

由 廉价感情. 提交于 2019-12-11 08:04:43
问题 I have one customized list MyList that extends ArrayList, like this: class MyList extends ArrayList<SomeParticularItem>{ [some methods...] } Since I have concurrent reads and writes to the list, I want to synchronize it: MyList mylist = (MyList) Collections.synchronizedList(new MyList()); This seems to be fine, the .jar is build. Then, at runtime, I get: java.util.Collections$SynchronizedRandomAccessList cannot be cast to MyList Is there a better way (is there any way at all) to obtain a

Does it make sense to synchronize web-service method?

由 China☆狼群 提交于 2019-12-11 07:33:41
问题 I'm creating a web-service written in Java and hosted on JBoss AS. I'm not a professional in web-service design yet but do I get it correctly and each call to the service initiates a new thread and not a new process? Does it make sense to have synchronized methods in my service? I need to have a method which is invoked only for one user at a time not simultaneously for multiple. 回答1: Yes, requests are handled by individual handler threads. There is a single process for all of JBoss.

java ConcurrentModificationException even with synchronized

由 白昼怎懂夜的黑 提交于 2019-12-11 07:24:44
问题 Similar issue has been posted before but this case is different - there is static usage which may be the complicating it. Just want to see if anyone has ideas on how to handle this. I get the ConcurrentModificationException even though I am using synchronzed on the list around both blocks that modify it. public class Foo { public void register() { FooManager.addFoo(this); } } public class ABC1 { static Foo myfoo; static { myfoo = new Foo(); myfoo.register(); } } (I have mutliple similar

synchronized notify, wait over property Boolean Object Java, IllegalMonitorStateException

由 青春壹個敷衍的年華 提交于 2019-12-11 06:06:21
问题 I have this code. import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; public class SyncProt0 { public static void main(String... args) { ExecutorService executorService = Executors.newCachedThreadPool(); ProcessStep psWorker = new ProcessStep(); ProcessStep psBoss = new ProcessStep(); Worker worker = new Worker

In java, can the use of synchronized methods be unreliable?

由 早过忘川 提交于 2019-12-11 05:13:32
问题 Going straight to the point, i have made a code to test concurrency in java, using synchronized methods: Code: public class ThreadTraining { public static class Value { private static int value; public static synchronized void Add() { value++; } public static synchronized void Sub() { value--; } public static synchronized int Get() { return value; } } public static class AddT implements Runnable { public static String name; public AddT(String n) { name = n; } @Override public void run() {

iOS Thread safety - Complete a block of code before thread switches

由 人走茶凉 提交于 2019-12-11 04:45:35
问题 I'm looking for a way to make sure that some lines of code get always executed together (before the system may switch the thread). @synchronized does not work for this as far as I know since it will only block another thread to come into this certain block. In my example I have different code parts that take influence on each other and I want to make sure that each of them blocks the other. How can this be achieved? EDIT: One Use Case could be that I'm playing back a midi file. The events go

IllegalMonitorStateException despite calling notifyAll() from synchronised context

由 人走茶凉 提交于 2019-12-11 04:37:35
问题 public class Alternate { static Boolean mutex = true; public static void main(String[] args) { Thread t1 = new Thread(new Odd(mutex)); Thread t2 = new Thread(new Even(mutex)); t1.start(); t2.start(); } } class Odd implements Runnable{ Boolean mutex; Odd( Boolean mutex){ this.mutex=mutex; } @Override public void run() { try { synchronized(mutex){ while(mutex){ mutex.wait(); } System.out.println("odd"); mutex=true; mutex.notifyAll(); Thread.sleep(500); } }catch (InterruptedException e) { e

Java/Android: Synchronized vs Queue implementation

由 不想你离开。 提交于 2019-12-11 03:58:47
问题 Can I ask a rookie Java question? I am downloading some files from the web. This method download(url location) is called multiple times. public static void download(final String url) { Thread t = new Thread("download") { @Override public void run() { try { synchronized (object) { // download & save } } catch(Exception e) {} } }; t.start(); } I added "synchronized" so that downloads happens one-by-one. (not multiple downloads occur at the same time). I am guessing even though download() is

Java并发编程系列-(3) 原子操作与CAS

由 余生颓废 提交于 2019-12-10 23:39:26
3. 原子操作与CAS 3.1 原子操作 所谓原子操作是指不会被线程调度机制打断的操作；这种操作一旦开始，就一直运行到结束，中间不会有任何context switch，也就是切换到另一个线程。 为了实现原子操作，Java中可以通过synchronized关键字将函数或者代码块包围，以实现操作的原子性。但是synchronized关键字有一些很显著的问题： 1、synchronized是基于阻塞锁的机制，如果被阻塞的线程优先级很高，可能很长时间其他线程都没有机会运行； 2、拿到锁的线程一直不释放锁，可能导致其他线程一直等待； 3、线程数量很多时，可能带来大量的竞争，消耗cpu，同时带来死锁或者其他安全。 像synchronized这种独占锁属于悲观锁，它是在假设一定会发生冲突的，那么加锁恰好有用，除此之外，还有乐观锁，乐观锁的含义就是假设没有发生冲突，那么我正好可以进行某项操作，如果要是发生冲突呢，那我就重试直到成功，乐观锁最常见的就是CAS。 JAVA内部在实现原子操作的类时都应用到了CAS。 3.2 CAS CAS是CompareAndSwap的缩写，即比较并替换。CAS需要有3个操作数：内存地址V，旧的预期值A，即将要更新的目标值B。 CAS指令执行时，当且仅当内存地址V的值与预期值A相等时，将内存地址V的值修改为B，否则就什么都不做。整个比较并替换的操作是一个原子操作

别翻了，这篇文章就是要让你搞定Java多线程！

由 孤人 提交于 2019-12-10 22:39:48
1. 理解线程与进程 由于并发肯定涉及到多线程，因此在进入并发编程主题之前，我们先来了解一下进程和线程的由来，这对后面对并发编程的理解将会有很大的帮助。 进程和线程的对比这一知识点由于过于基础，正因为过于基础，所以我们更应该透彻它！我们必须掌握什么是线程和进程，掌握线程与进程的关系、区别及优缺点 ！ 1.1、何为进程？ 首先我们来看一下进程的概念： 进程 ：是指一个内存中运行的应用程序，每个进程都有一个独立的内存空间，一个应用程序可以同时运行多个进程；进程也是程序的一次执行过程，是系统运行程序的基本单位；系统运行一个程序即是一个进程从创建、运行到消亡的过程。 看完之后，是不是感觉很抽象？很懵bi？懵bi就对了，说明你和我智商一样高....~开个玩笑~ 不妨先憋弃上面的概念，放松一下大脑，双击打开LOL，秒选德马打野，输了直接退出游戏并且保持微笑，然后正襟危坐心平气和的看宜春写的博客.... 这个时候的你不仅仅是愉快的撸了一把游戏，而且还亲自体验撸了一把进程...其实在你双击打开LOL的时候就已经创建了进程，此话怎讲？众所周知，我们的电脑安装的软件比如：LOL、微信、谷歌等等都是存储在我们的硬盘上的，硬盘上的数据可以说是永久存储（ORM）,当我们双击LOL的时候，LOL程序执行就进入了内存中，所有的程序必须进入内存中才能执行，内存属于临时存储（RAM），而
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