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Smuggling data in pointers
While reading up on The ABA Problem I came across a fantastic hack. The ABA problem, in a nutshell, results from the inability to atomically access both a pointer and a "marked" bit at the same time (read the wikipedia page). One fun, but very hackish solution is to "smuggle" data in a pointer. Example:#include "stdio.h"void * smuggle(void * ptr, int value){ return (void *)( (long long)ptr | (value & 3) );}int recoverData(void * ptr){ return (long long)ptr &...
Understanding GoLang interface
If goroutine and channel are considered as the foundation for GoLang concurrency, interface would be the key for data types in GoLang. In practical Go programming, almost all data types are built/used around interfaces, interface is the core of GoLang data structures. Go is not a typical OOP language, it has no class and inheritance concept syntactically. But it doesn't mean that there cannot be polymorphism in GoLang. Because of interface, it achieves the same polymorphism effect as in C++, tho...
Undefined property or variable in JavaScript
JavaScript is a weak type language, and also you can use a variable or property where it's undefined. If we don't have correct ways to check whether a property or variable is defined, we may get unexpected results when we try to access the,. How can we check whether a property or variable is undefined? This is actually a somewhat tricky question. Let's start off with some facts about undefined and then see what kind of function is consistent with the ones we care about. JavaScript attaches type...
Property,Undefined,Array,JavaScript 2014-07-24 06:56:07
JavaScript-style object literals in PHP
The object literal notation in JavaScript looks like: var fido = {name: "Fido", barks: true}; or var fido = {}; fido.name = "Fido"; fido.barks = true; From assoc arrays to objects In PHP you would call that an associative array. $fido = array( 'name' => "Fido", 'barks' => true ); And you can easily make it an object too: $fido = (object)$fido; echo gettype($fido); // "object" Or if you want to start with a blank object and add stuff to it: $fido = (object)array(); or $fido...
PHP,JavaScript,Object,Function call,Self vs this 2011-11-30 11:11:45
Ruby net-scp cannot scp multiple files with asterisk(*)
net-ssh/net-scp is a Ruby gem which can be used to scp files between different *nix machines. It's similar to how the *nix scp command. It can be used to scp a file or a directory. However, it seems it has some problem to scp multiple files using pattern *. For example, below script is supposed to download all files from remote directory to local directory: require 'net/scp' host = 'testmachine' login = 'testaccount' password = "testpassword" remote_path = '/tmp/remote...
NET-SCP,RUBY,ASTERISK,MULTIPLE FILES 2016-10-20 03:00:13
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
Binary tree iterator algorithm
Binary tree pre-order,in-order and post-order traversal are basics in algorithm and data structure.And the recursive binary tree traversal is a classical application of recursion. We define a binary tree node as : // C++ struct Node { int value; Node *left; Node *right; } In order binary tree traversal can be: // C++ void inorder_traverse(Node *node) { if (NULL != node->left) { inorder_traverse(node->left); } do_something(node); if (NULL != node->righ...
Binary tree,Iterator,Traversal 2013-07-14 21:51:09
JavaScript finite state machine
Finite state machine is a very useful design model, it can be used to simulate many events in the world. In short, finite state machine has three features: Number of states is finite At any moment, one object can only be in one state In some condition, it will transfer from one state to another state In JavaScript, finite state machine can be applied in many places. For example, one menu element on a webpage. When the mouse hovers on the menu, the menu will show up, while the mouse moves away...
JavaScript,Finite state machine,State 2013-09-02 11:00:57
A simple example on implementing progress bar in GoLang
Sometimes when handling a long running process, there would be need to track the progress so that people know something is still running instead of doubting something goes wrong. In this case, a progress bar which indicates the current status and progress would be desired. This post will show an example on how to implement progress bar using GoLang. Let's take a look at the final outcome first before jumping into the implementation detail. The key in the implementation is actually just the \r ...
TUTORIAL,EXAMPLE,GOLANG,PROGRESS BAR 2020-08-08 23:53:15
Overlap Detection
How does one detect when two strings overlap? In the case below, the four-letter suffix of string 1 matches the four-letter prefix of string 2. 1: "Fire at Will" 2: "William Riker is number one" Sometimes there are several matches; finding the longest is not always straight forward. 1: "Have some CoCo and CoCo" 2: "CoCo and CoCo is here." 2: "CoCo and CoCo is here." 2: "CoCo and CoCo is here." The naïve solution is to take...
String overlap,detection,python,implementation 2012-03-05 05:05:36
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