SEARCH KEYWORD -- EMPTY INTERFACE


  Something you may not know about Shell

Shell is also called command line interface, it is the interface between *nix users and computer. Shell is a program which provides service to access OS kernel services. This article is to introduce some not so well known but useful and interesting knowledge about shell. Wiki shell was born almost at the same time as Unix. The first UNIX shell was written by Ken Thompson in 1971 and its name is Thompson sh. It's older than Linux kernel. The default Shell in most *nix and MacOS is bash, bash was...

   Linux, Unix,Shell,Command     2012-11-24 07:19:47

  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

  Java AbstractMethodError explained and demonstrated

According to Oracle Java API documentation, AbstractMethodError is a kind of runtime error where the application is having some incompatible changes which leads to a missing implementation of an abstract method. Below is the official description. Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last co...

   JAVA,ABSTRACTMETHODERROR     2016-07-22 22:03:20

  Deep Understanding of ReentrantLock: Unlocking the Mysteries of Java Concurrent Programming

ReentrantLock introduction ReentrantLock is a class in the Java concurrent package, java.util.concurrent.locks, and is an implementation of the Lock interface. As its name suggests, it is a reentrant mutual exclusion lock. A mutual exclusion lock is a synchronization tool used to protect shared resources, ensuring that only one thread can access the resource at a given time. Reentrant means that a thread can acquire the same lock multiple times without causing a deadlock. This lock provides some...

   JAVA,REENTRANTLOCK,CONCURRENCY,MULTITHREADING     2023-05-22 08:01:13

  Will nil == nil be true in GoLang

There is some interview question may ask whether nil == nil be true in GoLang. Wil it be true. false or compilation error? To know the answer, some knowledge about nil in GoLang needs to be explained first. nil definition According to Go's official documentation, the definition of nil is // nil is a predeclared identifier representing the zero value for a // pointer, channel, func, interface, map, or slice type. var nil Type // Type must be a pointer, channel, func, interface, map, or slice type...

   GOLANG,NIL,NIL EXPLANATION     2021-08-08 02:54:15

  PHP to get access token for Twitter app

Previously we wrote an article about getting access token for Facebook app--PHP to get access token for Facebook app. Today we will introduce how to get access token for Twitter app using PHP. Since now Twitter is also using OAuth 2.0 to allow some web apps to access some users information on behalf of one user. They provided some APIs for developers to easily get them integrated with their own websites. The first step to get all these done is how to get the access token, the access token seems ...

   Twitter,OAuth,access token,PHP     2013-03-03 03:49:26

  Can two new objects point to the same memory address in GoLang?

Do you have any idea what the output will be for below GoLang snippet? package main import ( "fmt" ) type obj struct{} func main() { a := &obj{} fmt.Printf("%p\n", a) c := &obj{} fmt.Printf("%p\n", c) fmt.Println(a == c) } Many people would think that a and c are two different object instances which have different memory addresses. Hence a == c will be false. But if you try to run the above program, you would see below output 0x5781c8 0x5781c8 true To get to know the reason wh...

   GO,GOLANG,VARIABLE ESCAPE,ZEROBASE     2019-04-06 01:19:52

  WireGuard VPN Troubleshooting

When you are working as a network/cluster admin for you team to config the WireGuard VPN for other members, you may meet some of the problems below and these are the solution you can try to fix them. ----------------------------------------------------------------------------------------------------------- Problem [1]: The WireGuard handshake request send from the client can be received from the server but the server's response was blocked at some where so the client can not receive serv...

   WIREGUARD,VPN,TROUBLESHOOTING     2021-12-14 09:17:46

  About tmpfs

tmpfs is another confusing name in Linux kernel, its implementation is in mm/shmem.c, shmem has no relation to tmpfs at first glance although we know tmpfs is based on memory. We can understand why we use this name by seeing where this is used. In a desktop Linux system, tmpfs is loaded usually: % grep tmpfs /proc/mountsdevtmpfs /dev devtmpfs rw,seclabel,nosuid,relatime,size=1958956k,nr_inodes=489739,mode=755 0 0tmpfs /dev/shm tmpfs rw,seclabel,nosuid,nodev,relatime 0 0tmpfs /run tmpfs rw,seclab...

   tmpfs,Linux,file system     2013-06-14 12:10:56

  Use rsync to delete mass files quickly in Linux

Yesterday I encountered an issue to delete many log files in my Linux workstation, there were around 100,000 files to be deleted. These are log files and they grow very fast, and we need to delete them frequently. Usually we would use rm -rf * to delete these files, but we may need to wait for a relative long time if there are too many files. So we must adopt some unusual way. Fortunately, we can use rsync to delete mass files in one shot. 1. Install rsync yum install rsync 2. Create a new empty...

   rsync,delete file, demo     2012-11-13 10:44:50

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