Concurrency in Java
Littlethings makebigthings happens.
How to make thread-safe
You can create a new object for each method call
Sample code as SpelExpressionParser in Spring
public class SpelExpressionParser extends TemplateAwareExpressionParser {
//....
// Be noticed it will new a object each time, so it's thread safe
@Override
protected SpelExpression doParseExpression(String expressionString, @Nullable ParserContext context) throws ParseException {
return new InternalSpelExpressionParser(this.configuration).doParseExpression(expressionString, context);
}
}
:books:Concepts
Threads are sometimes called lightweight processes, and most modern operating systems treat threads, not processes, as the basic units of scheduling.
Liveness
While safety means "nothing bad ever happens", liveness concerns the complementary goal that "something good eventually happens".
A liveness failure occurs when an activity gets into a state such that it is permanently unable to make forward progress.
thread-safety
Whether an object needs to be thread-safe depends on whether it will be accessed from multiple threads. This is a property of how the object is used in a program, not what it does. Making an object thread-safe requires using synchronization to coordinate access to its mutable state; failing to do so could result in data corruption and other undesirable consequences.
Whenever more than one thread accesses a given state variable, and one of them might write to it, they all must coordinate their access to it using synchronization. The primary mechanism for synchronization in Java is the synchronized keyword, which provides exclusive locking, but the term “synchronization” also includes the use of volatile variables, explicit locks, and atomic variables.
How to fix broken multithreading
If multiple threads access the same mutable state variable without appropriate synchronization, your program is broken. There are three ways to fix it:
- Don’t share the state variable across threads;
- Make the state variable immutable;
- Use synchronization whenever accessing the state variable.
This “code confidence” is about as close as many of us get to correctness, so let’s just assume that single-threaded correctness is something that “we know it when we see it”.
A class is thread-safe when it continues to behave correctly when accessed from multiple threads.
A class is thread-safe if it behaves correctly when accessed from multiple threads, regardless of the scheduling or interleaving of the execution of those threads by the runtime environment, and with no additional synchronization or other coordination on the part of the calling code.
race condition
A race condition occurs when getting the right answer relies on lucky timing.
The most common type of race condition is check-then-act, where a potentially stale observation is used to make a decision on what to do next.
check-then-act
It is this invalidation of observations that characterizes most race conditions— using a potentially stale observation to make a decision or perform a computation. This type of race condition is called check-then-act: you observe something to be true (file X doesn’t exist) and then take action based on that observation (create X); but in fact the observation could have become invalid between the time you observed it and the time you acted on it (someone else created X in the meantime), causing a problem (unexpected exception, overwritten data, file corruption).
A common idiom that uses check-then-act is lazy initialization.
To ensure thread safety, check-then-act operations (like lazy initialization) and read-modify-write operations (like increment) must always be atomic.
Sample
this. @NotThreadSafe
public class LazyInitRace {
private ExpensiveObject instance = null;
public ExpensiveObject getInstance() {
if (instance == null)
instance = new ExpensiveObject();
return instance;
}
}
consequences
Like most concurrency errors, race conditions don’t always result in failure: some unlucky timing is also required. But race conditions can cause serious problems.
Intrinsic lock
Every Java object can implicitly act as a lock for purposes of synchronization; these built-in locks are called intrinsic locks or monitor locks. The lock is automatically acquired by the executing thread before entering a synchronized block and automatically released when control exits the synchronized block, whether by the normal control path or by throwing an exception out of the block.
Intrinsic locks in Java act as mutexes (or mutual exclusion locks), which means that at most one thread may own the lock. When thread A attempts to acquire a lock held by thread B, A must wait, or block, until B releases it. If B never releases the lock, A waits forever.
Reentrancy lock
Reentrancy means that locks are acquired on a per-thread rather than per-invocation basis.[7] Reentrancy is implemented by associating with each lock an acquisition count and an owning thread. When the count is zero, the lock is considered unheld.
When a thread acquires a previously unheld lock, the JVM records the owner and sets the acquisition count to one. If that same thread acquires the lock again, the count is incremented, and when the owning thread exits the synchronized block, the count is decremented. When the count reaches zero, the lock is released.
Guarding State with Locks
Because locks enable serialized access to the code paths they guard, we can use them to construct protocols for guaranteeing exclusive access to shared state. Following
However, just wrapping the compound action with a synchronized block is not sufficient; if synchronization is used to coordinate access to a variable, it is needed everywhere that variable is accessed. Further, when using locks to coordinate access to a variable, the same lock must be used wherever that variable is accessed.
It is a common mistake to assume that synchronization needs to be used only when writing to shared variables; this is simply not true. For each mutable state variable that may be accessed by more than one thread, all accesses to that variable must be performed with the same lock held. In this case, we say that the variable is guarded by that lock.
The fact that every object has a built-in lock is just a convenience so that you needn’t explicitly create lock objects.[9]
Every shared, mutable variable should be guarded by exactly one lock. Make it clear to maintainers which lock that is.
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你就会发现只要涉及递归的问题，都是 树的问题。
A Facial Recognition utility in a dozen of LOC
A Facial Recognition utility in a dozen of python LOC (Lines Of Code)
Awesome SSL certificates and HTTPS
What’s TLS TLS (Transport Layer Security) and its predecessor, SSL (Secure Sockets Layer), are security protocols designed to secure the communication betwee...
JVM warm up by Escape Analysis
Why JVM need warm up I don’t know how and why you get to this blog. But I know the key words in your mind are “warm” for JVM. As the name “warm up” suggested...
Java Concurrent Column 2
This is the second half about Java Concurrent of my blog
Java Concurrent
This blog is about noteworthy pivot points about Java Concurrent Framework Back to Java old days there were wait()/notify() which is error prone, while fr...
Algorithm notes from Leecode – 1
Algorithm Leetcode
2019
Conversations with God
Feelings is the language of the soul. If you want to know what’s true for you about something, look to how your’re feeling about.
Kafka In Spring
Enable Kafka listener annotated endpoints that are created under the covers by a AbstractListenerContainerFactory. To be used on Configuration classes as fol...
Terraform
Why Terraform
Kafka
Kafka
Mifid
FX Spot is not covered by the regulation, as it is not considered to be a financial instrument by ESMA, the European Union (EU) regulator. As FX is considere...
Foreign Exchange
currency pairs Direct ccy: means USD is part of currency pair Cross ccy: means ccy wihtout USD, so except NDF, the deal will be split to legs, both with...
2018
Seconds
nano seconds
Citrix receiver
Simple Binary Encoding (SBE)
Citrix receiver
“Cannot connect to remote desktop” with Citrix Receiver
Guice
A new type of Juice Put simply, Guice alleviates the need for factories and the use of new in your Java code. Think of Guice’s @Inject as the new new. You wi...
YAML
Key points All YAML files (regardless of their association with Ansible or not) can optionally begin with — and end with …. This is part of the YAML format a...
Distruptor
multithreading
Mockito
Feature
Protobuf
What are protocol buffers?
Sudo in a Nutshell
Sudo in a Nutshell Sudo (su “do”) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root...
Zoo-keeper
ZK Motto the motto “ZooKeeper: Because Coordinating Distributed Systems is a Zoo.”
Presto DB
WHAT IS PRESTO?
Chronicle
Overview
Cucumber
Acceptance testing vs unit test It’s sometimes said that unit tests ensure you build the thing right, whereas acceptance tests ensure you build the right thi...
Scala
Scala String
akka framework of scala
philosophy The actor model adopts the philosophy that everything is an actor. This is similar to the everything is an object philosophy used by some object-o...
File Util in Apache Camel
FileUtil.class
Apache Camel
Camel’s message model In Camel, there are two abstractions for modeling messages, both of which we’ll cover in this section. org.apache.camel.Message—The ...
QuickFixJ
Settings
JXM
Exporting your beans to JMX The core class in Spring’s JMX framework is the MBeanExporter. This class is responsible for taking your Spring beans and registe...
Solace MQ
Solace PubSub+ It is a message broker that lets you establish event-driven interactions between applications and microservices across hybrid cloud environmen...
Apigee
App deployment, configuration management and orchestration - all from one system. Ansible is powerful IT automation that you can learn quickly.
Ansible
Ansible: What Is It Good For? Ansible is often described as a configuration management tool, and is typically mentioned in the same breath as Chef, Puppet, a...
flexbox
How Flexbox works — explained with big, colorful, animated gifs
Jboss tips
commands:
Locking and multithreading
Single Writer principle
KDB
KDB However kdb+ evaluates expressions right-to-left. There are no precedence rules. The reason commonly given for this behaviour is that it is a much simple...
Foreign Exchange
Foreign Exchange markets
Portactor
Better to use smart wait
Agile and SCRUM
Key concept In Scrum, a team is cross functional, meaning everyone is needed to take a feature from idea to implementation.
DevOps-Philosophy
:100:DevOps Model Defined
rxjs pipe in depth
https://stormforger.com/blog/2016/07/08/types-of-performance-testing/
How to setup nodejs to install package from intranet
Error of ‘ECONNRESET’ You may face error ECONNRESET from intranet, even appropriate proxy tools (e.g. cntlm) is running. The errors may looks like ```bash $ ...
Strategy-Of-Openshift-Releases
Release & Testing Strategy There are various methods for safely releasing changes to Production. Each team must select what is appropriate for their own ...
NodeJs Notes
commands to read files var lineReader = require(‘readline’).createInterface({ input: require(‘fs’).createReadStream(‘C:\dev\node\input\git_reset_files.tx...
Minium Viable Product
https://blog.leanstack.com/minimum-viable-product-mvp-7e280b0b9418
What is difference between declarations, providers and import in NgModule
What is difference between declarations, providers and import in NgModule
CORS :Cross-Origin Resource Sharing
Cross-Origin Request Sharing - CORS (A.K.A. Cross-Domain AJAX request) is an issue that most web developers might encounter, according to Same-Origin-Policy,...
ngrx
Why @Effects? In a simple ngrx/store project without ngrx/effects there is really no good place to put your async calls. Suppose a user clicks on a button or...
iOS programming
View A view is also a responder (UIView is a subclass of UIResponder). This means that a view is subject to user interactions, such as taps and swipes. Thus,...
2017
cloud computering
openshift vs openstack The shoft and direct answer is `OpenShift Origin can run on top of OpenStack. They are complementary projects that work well together....
cloud computering
Concepts Cloud computing is the on-demand demand delivery of compute database storage applications and other IT resources through a cloud services platform v...
Redux
whats @Effects You can almost think of your Effects as special kinds of reducer functions that are meant to be a place for you to put your async calls in suc...
reactive programing
The second advantage to a lazy subscription is that the observable doesn’t hold onto data by default. In the previous example, each event generated by the in...
common errors in NPM or node
code E503 code E503 when run npm install packages, e.g.
Container
The Docker project was responsible for popularizing container development in Linux systems. The original project defined a command and service (both named do...
promise vs observiable
The drawback of using Promises is that they’re unable to handle data sources that produce more than one value, like mouse movements or sequences of bytes in ...
Openshift tips
Commands bible
google analysis
How Page Value is calculated
JDK source
interface RandomAccess Marker interface used by List implementations to indicate that they support fast (generally constant time) random access. The primary ...
SSH SFTP
Secure FTP SFTP over FTP is the equivalant of HTTPS over HTTP, the security version
Setup WebSphere profiles and application in command line
Setup WebSphere profiles and application in command line
AWS Tips
After establishing a SSH session, you can install a default web server by executing sudo yum install httpd -y. To start the web server, type sudo service htt...
Oracle
ORA-12899: Value Too Large for Column
Spring notes
Spring Bean Life Cycle Callback Methods
Kindle notes
#《亿级流量网站架构核心技术》目录一览 TCP四层负载均衡 使用Hystrix实现隔离 基于Servlet3实现请求隔离 限流算法 令牌桶算法 漏桶算法 分布式限流 redis+lua实现 Nginx+Lua实现 使用sharding-jdbc分库分表 Disruptor+Redis...
Java JIT compiler
This is talking about Java JIT (Just-In-Time) compiler
Java Security Notes
Java Security well-behaved: programs should be prevent from consuming too much system resources
SeriableVersionUID
Noteworthy points about SeriableVersionUID in Java
R Language
s<-read.csv("C:/Users/xxx/dev/R/IRS/SHH_SCHISHG.csv") # aggregate s2<-table(s$Original.CP) s3<-as.data.frame(s2) # extract by Frequency ordered s3...
SSH and Cryptography
SFTP versus FTPS SS: Secure Shell An increasing number of our customers are looking to move away from standard FTP for transferring data, so we are ofte...
Eclipse notes
How do I remove a plug-in? Run Help > About Eclipse > Installation Details, select the software you no longer want and click Uninstall. (On Macintosh i...
Java JVM
Class loading subsystem
Maven-Notes
Maven philosophy “It is important to note that in the pom.xml file you specify the what and not the how. The pom.xml file can also serve as a documentatio...
Java New IO
Notes JDK 1.0 introduced rudimentary I/O facilities for accessing the file system (to create a directory, remove a file, or perform another task), accessi...
Network Protocols
Net Protocols
IT-Architect
SOA SOA is a set of design principles for building a suite of interoperable, flexible and reusable services based architecture. top-down and bottom-up a...
Algorithm
This page is about key points about Algorithm
Dead Lock
Concept
Java-Tricky-Tech-Questions.md
What is the difference between Serializable and Externalizable in Java? In earlier version of Java, reflection was very slow, and so serializaing large ob...
NavigableMap Misc
What is NavigableMap
Compare-In-Java
Concepts If you implement Comparable interface and override compareTo() method it must be consistent with equals() method i.e. for equal object by equals(...
Java Collections Misc
Difference between equals and deepEquals of Arrays in Java Arrays.equals() method does not compare recursively if an array contains another array on oth...
HashMap in JDK
Hashmap in JDK Some note worth points about hashmap Lookup process Step# 1: Quickly determine the bucket number in which this element may resid...
Java 8 Tips
This blog is listing key new features introduced in Java 8
Arbitrage vs Heading
What is the difference between arbitrage and hedging?
Java Enum Misc
Enum Misc
2016
Java GC notes
verbose:gc verbose:gc prints right after each gc collection and prints details about each generation memory details. Here is blog on how to read verbose gc
Hash Code Misc
contract of hashCode : Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consis...
Apache Tips
Apache
Angulary Misc
Dependency Injection Angular doesn’t automatically know how you want to create instances of your services or the injector to create your service. You must co...
Random number in java
ThreadLocalRandom, SecureRandm, java.util.Random, java.math.Random
Java new features
JDK Versions JDK 1.5 in 2005 JDK 1.6 in 2006 JDK 1.7 in 2011 JDK 1.8 in 2014 Sun之前风光无限，但是在2010年1月27号被Oracle收购。 在被Oracle收购后对外承诺要回到每2年一个realse的节奏。但是20...
用10几行代码自己写个人脸识别程序
用10几行代码自己写个人脸识别程序
Eslastic Search
Eslastic Search
JSON lines
JSON lines
Python Scraphy
Python Scraphy
Simpler chronicle of CI(Continuous Integration) “乱弹系列”之持续集成工具
引言 有句话说有人的地方就有江湖，同样，有江湖的地方就有恩怨。在软件行业历史长河（虽然相对于其他行业来说，软件行业的历史实在太短了，但是确是充满了智慧的碰撞也是十分的精彩）中有一些恩怨情愁，分分合合的小故事，比如类似的有，从一套代码发展出来后面由于合同到期就分道扬镳，然后各自发展成独门产品的Sybase DB和微...
Head First Blockchina 3
Hyperledger Fabric for Mortals
【原创】深入浅出区块链系统：第二章
使用Solidity创建以太坊(Ethereum)智能合约(Smart Contract)
How to customize Sublime syntax highlights
Reference Sublime Scope Naming Syntax Guide
浅谈软件单元测试中的“断言” (assert)，从石器时代进步到黄金时代。
大家都知道，在软件测试特别是在单元测试时,必用的一个功能就是“断言”（Assert)，可能有些人觉得不就一个Assert语句，没啥花头，也有很多人用起来也是懵懵懂懂，认为只要是Assert开头的方法，拿过来就用。一个偶然的机会跟人聊到此功能，觉得还是有必要在此整理一下如何使用以及对“断言”的理解。希望可以帮助大家...
Head First Blockchina 1
深入浅出区块链系统：第一章. what you should know about blockchain
Kubernetes 与 Docker Swarm的对比
Kubernetes 和Docker Swarm 可能是使用最广泛的工具，用于在集群环境中部署容器。但是这两个工具还是有很大的差别。
漫谈开发设计中的一些‘原则’及’设计哲学’
在开发设计中有一些常用原则或者潜规则，根据笔者的经验，这里稍微总结一下最最常用的，以飨读者。
http methods
RFC origion http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2)
Spark-vs-Storm
The stark difference among Spark and Storm. Although both are claimed to process the streaming data in real time. But Spark processes it as micro-batches; wh...
微服务
可以想像一下，之前的传统应用系统，像是一个大办公室里面，有各个部门，销售部，采购部，财务部。办一件事情效率比较高。但是也有一些弊端，首先，各部门都在一个房间里。
unmodifiableList, unmodifiableSet,unmodifiableMap
What’s it Returns an unmodifiable view of the specified set. This method allows modules to provide users with “read-only” access to internal sets. Query ope...
kibana, view layer of elasticsearch
What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...
kibana, view layer of elasticsearch
What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...
Anatomy of ThreadLocal
Design philosophies
iConnect
UI HTML5, AngularJS, BootStrap, REST API, JSON Backend Hadoop core (HDFS), Hive, HBase, MapReduce, Oozie, Pig, Solr
Business Analysis
Purpose of BA 带来一些商业价值（收益） 解决业务痛点
Something about RESTful architect
REST API must be hypertext driver Roy’s interview
Data Structure
Binary Tree A binary tree is a tree in which no node can have more than two children. A property of a binary tree that is sometimes important is that th...
Useful bookmarks
eBooks list of various books Node.js
heavy load web application
Common solutions
tips in as400 IBM Emulator
Toggle crosshair
Mysql operator to extract JSON
“Be the change you wish to see in the world.” - Mahatma Gandhi
equity trading
Difference between mutal funds and hedge funds
SQL
Differences between not in, not exists , and left join with null
HTTPS/2
concepts
Github page commands notes
404 error for customized domain (such as godday) 404 There is not a GitHub Pages site here. Go to github master branch for gitpages site, manually add CN...
RenMinBi International
RQFII RQFII stands for Renminbi Qualified Foreign Institutional Investor. RQFII was introduced in 2011 to allow qualified foreign institutional investors to ...
JavaScript tips
includes() vs some()
Docker Errors and Fixes
Docker Errors
Load Balancing
Concepts LVS means Linux Virtual Server, which is one Linux built-in component.
Python
(‘—–Unexpected error:’, <type ‘exceptions.TypeError’>) datetime.datetime.now()
Storage Management
RAID RAID is Reductant Array Independent Disk,
CI and CD
Concepts
XA Transactions in 2PC
Description
Setup Git in Mint Linux
How to setup Git in Mint Linux =================================================
Database sharding
DB sharding in YHD
Microservices vs. SOA
Microservice Services are organized around capabilities, e.g., user interface front-end, recommendation, logistics, billing, etc. Services are small in ...
Java Class Loader
Codecache The maximum size of the code cache is set via the -XX:ReservedCodeCacheSize=N flag (where N is the default just mentioned for the particular com...