hadoop simple explanation

The simple explanation and practice of the Android event bus distribution library Eventbus Introduction, Eventbus Everyone should be unfamiliar, Eventbus is an Android-optimized publish/Subscribe event bus. The main function is to substitute intent,handler,broadcast for passing messages between Fragment,activity,service and threads. The advantage is that the cost is small and the code is more elega

who goes in takes a key and hangs the key back when he comes out. After the people found that the key was overhead, they knew they had to wait in line at the door. This is called a "semaphore" (Semaphore), which guarantees that multiple threads do not conflict with each other.It is not difficult to see that a mutex is a special case of Semaphore (N=1). That is, it is entirely possible to replace the former with the latter. However, because the mutex is simpler and more efficient, this design is

This article is reproduced from Nanyi's blog " A simple explanation of processes and threads ". Processes (process) and threads (thread) are the basic concepts of the operating system, but they are abstract and difficult to master.Recently, I read a piece of material and found that there is a good analogy that can be explained in a clear and understandable way.1.　　The core of the computer is the CPU, which

script to run less quickly, which requires the time library, such as 0.5 seconds each request interval: time.sleep (0.5), or add the random library, so: Time.sleep ( Random.random () * *)Automated test Tools SeleniumWhy put selenium to the end, because it can solve most of the anti-crawling! Yes, this library is so powerful!Here is not detailed, then open a single article, we slowly say! Or that sentence, learning itself is a long process, we need constant practice to enhance our interest in le

. If this is not done, it will exit instead of remaining on the remote terminal. If you just log in past to execute#!/usr/bin/expect# Note the path of the installation, not sure whereisexpect a bit#ChangealoginshelltobashSETUSER[LINDEX$ARGV0]Spawnbash$userExpect "]:"Send "/bin/bash"ExpecteofExitSpawn represents the statement executed at the local terminal, and after the statement begins execution, expect starts capturing the terminal's output information and then makes the corresponding operatio

-coordinate. Well, it's not easy to say that, a little off my title, or simply rude to explain that the matrix is replaced by: (A,B,C,D,E,F) six values, and then calculates the relative coordinates of each pixel according to the center point, and then calculates the new coordinates, the new coordinates are calculated as:X ' = a * x + c * y + E; Y ' = b * x + d * y + F; When rotate, the cosθ,sinθ,sinθ, and cos θ are passed in, while skew values are: Cosθ/consθ , sin θ/cosθ , sinθ/cosθ , cosθ/cosθ

In Linux, the main editor is VI or VIM, this article around vim to do a simple explanation: Linux default self-contained VI (VIM) editor, its package is: [[emailprotected] ~]# rpm-qf ' which VI ' vim-minimal-7.2.411-1.8.el6.x86_64 [[emailprotected] ~]# rpm-qf ' which vim ' vim-enhanced-7.2.411-1.8.el6.x86_ 64vim Editor Mode toggle: Command mode, command line mode, edit mode command mode: Character manipulat

://s3.51cto.com/wyfs02/M01/60/39/wKioL1UqhPrjJAynAADXMlA4XlY181.jpg "title=" 88.png "alt=" Wkiol1uqhprjjaynaadxmla4xly181.jpg "/>Log in to the master database to see if the user table has data written;650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/60/3D/wKioL1UqhZaB3XDiAAFZsmBMkyQ007.jpg "title=" 99.png "alt=" Wkiol1uqhzab3xdiaafzsmbmkyq007.jpg "/>Log in to the slave database to see if the corresponding table has data synchronization.I have synchronized here, too lazy to write, exhau

.Description0 default value before action is taken1 release Pagecache2 Releasing Dentries and Inodes3 releasing Pagecache, Dentries and InodesThe actual operation can use the following sysctl, also can use echo 3 >/proc/sys/vm/drop_caches, the same effect![Email protected] ~]# sysctl vm.drop_caches=3vm.drop_caches=3[[Email protected]~]# free-m total used free shared buffers Cachedmem:996 the 907 0 0 A-/+ Buffers/cache: the 920Swap:2047 455

period.The timeout class, created internally, is returned from settimeout () and SetInterval (). Can be passed to cleartimeout () and Clearinterval () to cancel the scheduled operationWhen you book a timeout timer class, the Nodejs event loop mechanism continues to run as long as the timer is active. The default behavior of the timer can also be controlled through the ref () and unref () functions.When Timeout.ref () is called, the event loop is required to not exit as long as the timer is acti

string. The function returns a pointer to the final target string destAs an example:#include #includestring.h>intMain () {Chard[ -] ="Goldenglobal"; Char* s ="View"; strcat (d,s); printf ("%s", D); GetChar (); return 0;}The printing results are as follows:Let me give you an easy-to-understand example:#include #includestring.h>intMain () {Charstr[ the]; strcpy (str,"these"); strcat (str,"Strings"); strcat (str," is"); strcat (str,"concatenated."); Puts (str); return 0;}The printing r

Android IOC annotation binding control and event case code simple annotation explanation, androidioc I think android has used some frameworks. However, some annotations are used in the frameworks to help us and save a lot of code development workload. It also makes the code more concise. However, annotations are implemented through java reflection and may sacrifice some performance. The following is a

. Remember AsyncTask the code inside the constructor: Public Asynctask() {Mworker =NewWorkerrunnable PublicResultPager()throwsException {Mtaskinvoked.set (true); Process.setthreadpriority (Process.thread_priority_background);//noinspection UncheckedResult result = Doinbackground (mparams); Binder.flushpendingcommands ();returnPostresult (result); } }; Mfuture =NewFuturetask@Override protected void Done() {Try{postresultifnotinvoked (get ()); }Catch(Interruptedexception

N keys at the door. The person who goes in takes a key and hangs the key back when he comes out. After the people found that the key was overhead, they knew they had to wait in line at the door. This is called a "semaphore" (Semaphore), which guarantees that multiple threads do not conflict with each other. It is not difficult to see that a mutex is a special case of Semaphore (N=1). That is, it is entirely possible to replace the former with the latter. However, because the mutex is simpler an

threads.10.The solution at this point is to hang N keys at the door. The person who goes in takes a key and hangs the key back when he comes out. After the people found that the key was overhead, they knew they had to wait in line at the door. This is called a "semaphore" (Semaphore), which guarantees that multiple threads do not conflict with each other.It is not difficult to see that a mutex is a special case of Semaphore (N=1). That is, it is entirely possible to replace the former with the

person who goes in takes a key and hangs the key back when he comes out. After the people found that the key was overhead, they knew they had to wait in line at the door. This is called a "semaphore"(Semaphore), which guarantees that multiple threads do not conflict with each other. It is not difficult to see that a mutex is a special case of Semaphore (N=1). That is, it is entirely possible to replace the former with the latter. However, because the mutex is simpler and more efficient, this de