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  PHP advisory file lock : flock

When we process a file in PHP, we may often need to acquire a lock so that other scripts cannot edit the same file at the same time. There is a flock() function in PHP which can help us lock the file we want to process. But there is one issue we should take care. Recently, ffb encountered one issue while he was trying to lock a file handle. The codes are below: $filename = "/tmp/lock.txt";      $fp = fopen($filename, "r+");   if (!$fp...

   flock(),advisory locking,PHP     2013-04-23 11:42:48

  Service discovery with etcd

In previous post, we have talked about etcd and its usage. This post we will cover how to implement server discovery with etcd. Service discovery is to solve one of the most commonly seen scenarios in distributed system where how to find the corresponding target service to talk to. In short, it is to find some server which one can talk to based on some service name. A complete service discovery system include below three key functions: Service registration: A service must register itself to so...

   ETCD,SERVICE DISCOVERY,DEMO,TUTORIAL     2021-03-08 05:36:29

  Difference between ConcurrentHashMap and Hashtable

Both ConcurrentHashMap and Hashtable are Collection classes for storing key value pairs and they both provide fast element search with a supplied key. They have much in common. However, we will not discuss the similarities between them here, instead we will focus on the differences between them. ConcurrentHashMap and Hashtable are both thread safe. But the mechanism for thread safe is different between them. Hashtable is synchronized, it utilizes the synchronization mechanism; while ConcurrentHa...

   ConcurrentHashMap,Hashtable     2013-11-18 08:06:54

  Microsoft’s “Picture Password”: A Breath Of Fresh Air On The Lock Screen, Of All Places

Remember that feeling you got back when Steve Jobs was unveiling the iPhone, and he did the “slide to unlock” gesture for the first time? I remember the way he said it – “You like that? Want to see it again?” Since then I haven’t seen a lock screen interface that has made me feel that same “how obvious, how elegant!” feeling – until today at the NVIDIA press conference, and later at the Microsoft keynote here at CES. It sounds a little silly...

   Microsoft,Windows 8,Picture Password,CES     2012-01-10 06:55:28

  Simple explanation about process and thread

Process and thread are two basic concepts of operating system, but they are a bit abstract which cannot be  mastered easily. There is an analogy which explains these concepts very well. 1. The kernel of the computer is CPU, it handles all the computing tasks, it's like a factory and will run all the time. 2. Assume there is power limitation for the factory, it can only supply to one unit once,i.e, when one unit is working, other units must stop and wait. The meaning behind this is that eac...

   Process,Thread,CPU,Operating system     2013-04-24 11:33:10

  10 major updates of Windows 8.1

Last night, the 2013 Microsoft Build Developer Conference started in San Francisco. The highlight of the first day is Microsoft CEO Steve Ballmer announced the release of Windows 8.1 Preview . The final version will be released in November and he also mentioned that there would be over 300 updates on the new OS. Now let's summarize 10 major updates of the new OS. 1. Classical desktop mode After getting a lot of feedback from users, Microsoft adds a new setting. Users can choose to start in clas...

   Windows 8.1,Build     2013-06-27 05:45:02

  Recursive class initialization in Java

When a Java class is referenced and initialized, it has to go through the loading and linking first. Once the loading and linking complete successfully. The class will be initialized. The static variables and constant variables will be initialized during this process. Once the class is initialized, it is ready for use. If when class A is initialized and it is referencing a class B, the class B will also get initialized. But what will happen if class B is referencing class A as well? This is call...

   Java,JVM,class initialization,static final     2015-04-15 21:04:29

  What is cache penetration, cache breakdown and cache avalanche?

When designing and developing highly available system, cache is an very important consideration. It is useful to cache some frequently accessed data so that they can be accessed quickly and also cache can protect the downstream system like DB from being hit too often.  To provide better cache design in large systems, some problems may need to be considered first. In this post, we will talk about some frequently discussed cache problems and mitigation plans. Cache penetration Cache penetrati...

   SYSTEM DESIGN,CACHE PENETRATION,CACHE BREAKDOWN,CACHE AVALANCHE     2020-04-10 08:43:00

  Emacs adventures

I have been using Emacs for over a year now. I actually didn’t learn a lot when I started using it (just the basics to get going and then some relatively common keyboard shortcuts), but lately I have been reading and learning much more about it. I’m so grateful by everything I’ve learned from different people on the net that I wanted to share a couple of things I’ve learned, and a simple major mode for editing AsciiDoc documents. As a long-time VIM user, I f...

   Editor,Linux,Emacx,VIM,Shortcuts     2011-11-30 11:56:49

  Useful Bash Scripts

Many people hack together shell scripts quickly to do simple tasks, but these soon take on a life of their own. Unfortunately shell scripts are full of subtle effects which result in scripts failing in unusual ways. It's possible to write scripts which minimise these problems. In this article, I explain several techniques for writing robust bash scripts. Use set -u ...

   Linux,Shell,Bash,Command,Robust     2012-01-15 10:28:00

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