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coldmund · 9 years ago

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Rvalue references & Move semantics (c++)

Rvalue references

C++의 lvalue는 named variable처럼 주소를 얻을 수 있는 것이며 rvalue는 그렇지 않은 것이다(예를 들어 상수, 임시 객체나 값).

rvalue reference는 rvalue에 대한 참조이며, 특히 rvalue가 임시객체일 경우 적용된다.

rvalue reference의 목적은 임시 객체가 사용될 경우 특정 함수를 선택할 수 있도록 하는 것이며 이를 이용해 덩치 큰 객체의 ��사를 pointer의 복사로 구현할 수 있다.

함수의 parameter에 &&를 추가하여 표시한다(ex. type &&name). 정확히는 universal reference라고 한다던가...

일반적으로 임시객체는 const type&로 표시하지만 rvalue reference를 사용하는 overload된 함수가 있을 경우 임시 객체는 해당 함수로 처리된다.

// 1. lvalue reference void incr(int &value) { cout << "increment with lvalue reference" << endl; ++value; } // 2. rvalue reference void incr(int &&value) { cout << "increment with rvalue reference" << endl; ++value; } int a = 10, b = 20; incr(a); // call 1. incr(a + b); // call 2. incr(3); // call 2. incr(std::move(b)) // call 2.

Move semantics

object에 move semantics를 사용하기 위해서는 move constructor와 move assignment operator가 필요하다. 둘 다 source object로부터 member variable을 복사하고 source object의 variable은 null value로 초기화한다(shallow copy).

move constructor와 move assignment operator는 모두 noexcpet여야 한다.

class Spreadsheet { public: Spreadsheet(Spreadsheet &&src) noexcept; Spreadsheet &operator=(Spreadsheet &&rhs) noexcept; }; Spreadsheet::Spreadsheet(Spreadsheet &&src) noexcept { mCells = src.mCells; ... src.mCells = nullptr; ... } Spreadsheet &Spreadsheet::operator=(Spreadsheet &&rhs) noexcept { if(this == &rhs) return *this; freeMemory(); // remove previous value mCells = rhs.mCells; ... rhs.mCells = nullptr; ... return *this; }

move constructor와 move assignment operator가 없을 경우 copy constructor와 assignment operator가 사용되며 그 경우 위 code의 src.mCells = nullptr 대신 메모리 할당과 복사가 발생한다.

move constructor와 move assignment operator는 명시적으로 삭제되거나 기본값처리할 수 있다(explicitly deleted or defaulted).

std::move() 함수는 실제로 아무것도 옮기지 않는다. lvalue reference를 rvalue reference로 바꿀 뿐이다(EMC++).

rvalue를 assign할 경우 std::move() 함수를 명시적으로 호출하지 않아도 move assignment operator가 호출된다.

#include <iostream> #include <utility> class Foo { public: Foo() { std::cout << "constructor" << std::endl; } Foo(Foo &f) { std::cout << "copy constructor" << std::endl; } Foo(Foo &&f) noexcept { std::cout << "move constructor" << std::endl; } Foo &operator=(const Foo &f) { std::cout << "assignment" << std::endl; } Foo &operator=(const Foo &&f) noexcept { std::cout << "move assignment" << std::endl; } }; Foo f1() { Foo f; return f; } Foo f2() { return f1(); } int main(int argc, char **argv) { Foo f; std::cout << "TEST1" << std::endl; f = f1(); // move assignment std::cout << "TEST2" << std::endl; f = std::move(f1()); // move assignment std::cout << "TEST3" << std::endl; f = f2(); // move assignment std::cout << "TEST4" << std::endl; f = std::move(f2()); // move assignment return 0; }

#c++#cpp #pc++

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purejust · 3 years ago

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Purebasic image memory allocation

Salts by definition are meant to be cryptographically secure random data, not static/hard-coded constants. Saki wrote: ↑ Mon 8:57 pmThis is a static salt. Repeat : Until WaitWindowEvent()=#PB_Event_CloseWindow MessageRequester("Hint", "Decrypted Image not usable") WindowHeight(window_ID)/2-ImageHeight(image_ID)/2, WindowWidth(window_ID)/2-ImageWidth(image_ID)/2, If UCase(GetExtensionPart(source_path_image$))"GIF" : ResizeImage(image_ID, 300, 300) : EndIfĭefine image_gadget_ID=ImageGadget(#PB_Any, If recreate_image_file : If Not image_ID : MessageRequester("Hint", "Can not create a decrypted image") : EndIf : End : EndIfĭefine window_ID=OpenWindow(#PB_Any, 0, 0, 650, 400, "Decrypted Image", #PB_Window_SystemMenu|#PB_Window_ScreenCentered) UsePNGImageDecoder() : UseJPEGImageDecoder() : UseTIFFImageDecoder() : UseGIFImageDecoder()ĭefine recreate_image_file=0 Recreate a decrypted image from a encrypted imageĭefine image_ID=LoadImage_and_Decrypt_BF(source_path_image$, password$, recreate_image_file) If Not image_ID : ProcedureReturn -6 : EndIf : ProcedureReturn image_ID Protected image_ID=CatchImage(#PB_Any, *buffer_1, length) : FreeMemory(*buffer_1) If WriteData(file, *buffer_1, length)length : CloseFile(file) : FreeMemory(*buffer_1) : ProcedureReturn -22 : EndIf If Not file : ProcedureReturn -21 : EndIf Source_path_image$=RemoveString(source_path_image$, crypt_extender$, #PB_String_NoCase)įile=CreateFile(#PB_Any, source_path_image$) If Not AESDecoder(*buffer, *buffer_1, length, 256, #PB_Cipher_CBC)įreeMemory(*buffer) : FreeMemory(*buffer_1) : CloseFile(file) : ProcedureReturn -9 Protected *buffer_1=AllocateMemory(length) : If Not *buffer_1 : FreeMemory(*buffer) : ProcedureReturn -9 : EndIf If ReadData(file, *buffer, length)length : FreeMemory(*buffer) : CloseFile(file) : ProcedureReturn -21 : EndIf Repeat 32 2))) : ii+SizeOf(character)16 : CloseFile(file) : ProcedureReturn -21 : EndIf : FileSeek(file, 0) Protected fixed$=StringFingerprint(password$+"%$(s4DäÖÄö", #PB_Cipher_SHA3), i, ii : Dim register.q(5) UseSHA3Fingerprint() By Saki - Advanced AES CBC mode image Decrypter with crypt randomized IV Procedure LoadImage_and_Decrypt_BF(source_path_image$, password$, recreate_file=0, crypt_extender$=" ") LoadImage_Encrypt_and_Save_BF(source_path_image$, destination_path_image$, password$) Repeat 32 2))) : ii+SizeOf(character)length+16 : FreeMemory(*buffer_1) : CloseFile(file) : ProcedureReturn -22 : EndIfĭefine source_path_image$=OpenFileRequester("Select a image", "", "", 0) : If source_path_image$="" : End : EndIfĭefine destination_path_image$=source_path_image$ Protected extension$="."+GetExtensionPart(source_path_image$)ĭestination_path_image$=GetPathPart(source_path_image$)+GetFilePart(source_path_image$)ĭestination_path_image$=RemoveString(destination_path_image$, extension$) : destination_path_image$+crypt_extender$+extension$ Protected fixed$=StringFingerprint(password$+"%$(s4DäÖÄö", #PB_Cipher_SHA3), i, ii, *buffer : Dim register.q(5) UseSHA3Fingerprint() By Saki - Advanced AES CBC mode image Encrypter with crypt randomized IV Procedure LoadImage_Encrypt_and_Save_BF(source_path_image$, destination_path_image$, password$, crypt_extender$=" ")

#Purebasic image memory allocation

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hptposts · 6 years ago

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Java Multithreading

3) Running

The thread is in running state if the thread scheduler has selected it.

Create Thread:

Thread()

Thread(String name)

Thread(Runnable r)

Thread(Runnable r,String name)

used method:

run, start, sleep, join, join milis, getPriority, setPriority, getName, setName, currentThread, getId, getState, isAlive, yield, suspend, resump, stop, isDaemon, setDaemon, interrupt, isInterrupted, interrupted.

Start thread:

- by runnable, by extend Thread

Thread Scheduler in Java

Thread scheduler in java is the part of the JVM that decides which thread should run.

There is no guarantee that which runnable thread will be chosen to run by the thread scheduler.

Only one thread at a time can run in a single process.

The thread scheduler mainly uses preemptive or time slicing scheduling to schedule the threads.

Difference between preemptive scheduling and time slicing

Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

Thread.sleep(500)

start a Thread twice:

running Exception in thread "main" java.lang.IllegalThreadStateException

call run() -> only one 1 stack

join thread, naming thread, thread priority (high = strong)

Daemon thread:

Daemon Thread in Java

Daemon thread in java is a service provider thread that provides services to the user thread. Its life depend on the mercy of user threads i.e. when all the user threads dies, JVM terminates this thread automatically.

There are many java daemon threads running automatically e.g. gc, finalizer etc.

You can see all the detail by typing the jconsole in the command prompt. The jconsole tool provides information about the loaded classes, memory usage, running threads etc.

Points to remember for Daemon Thread in Java

It provides services to user threads for background supporting tasks. It has no role in life than to serve user threads.

Its life depends on user threads.

It is a low priority thread.

ThreadPool:

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

class WorkerThread implements Runnable {

private String message;

public WorkerThread(String s){

this.message=s;

}

public void run() {

System.out.println(Thread.currentThread().getName()+" (Start) message = "+message);

processmessage();//call processmessage method that sleeps the thread for 2 seconds

System.out.println(Thread.currentThread().getName()+" (End)");//prints thread name

}

private void processmessage() {

try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); }

}

File: JavaThreadPoolExample.java

public class TestThreadPool {

public static void main(String[] args) {

ExecutorService executor = Executors.newFixedThreadPool(5);//creating a pool of 5 threads

for (int i = 0; i < 10; i++) {

Runnable worker = new WorkerThread("" + i);

executor.execute(worker);//calling execute method of ExecutorService

}

executor.shutdown();

while (!executor.isTerminated()) { }

System.out.println("Finished all threads");

}

ThreadGroup in Java

Java provides a convenient way to group multiple threads in a single object. In such way, we can suspend, resume or interrupt group of threads by a single method call.

Java Shutdown Hook

The shutdown hook can be used to perform cleanup resource or save the state when JVM shuts down normally or abruptly. Performing clean resource means closing log file, sending some alerts or something else. So if you want to execute some code before JVM shuts down, use shutdown hook.

When does the JVM shut down?The JVM shuts down when:

user presses ctrl+c on the command prompt

System.exit(int) method is invoked

user logoff

user shutdown etc.

If you have to perform single task by many threads, have only one run() method.For example:

class TestMultitasking2 implements Runnable{

public void run(){

System.out.println("task one");

}

public static void main(String args[]){

Thread t1 =new Thread(new TestMultitasking2());//passing annonymous object of TestMultitasking2 class

Thread t2 =new Thread(new TestMultitasking2());

t1.start();

t2.start();

}

If you have to perform multiple tasks by multiple threads,have multiple run() methods.For example: --

Java Garba@ge Collection

In java, garbage means unreferenced objects.

Garbage Collection is process of reclaiming the runtime unused memory automatically. In other words, it is a way to destroy the unused objects.

To do so, we were using free() function in C language and delete() in C++. But, in java it is performed automatically. So, java provides better memory management.

Advantage of Garbage Collection

It makes java memory efficient because garbage collector removes the unreferenced objects from heap memory.

It is automatically done by the garbage collector(a part of JVM) so we don't need to make extra efforts.

Java Runtime class

Java Runtime class is used to interact with java runtime environment. Java Runtime class provides methods to execute a process, invoke GC, get total and free memory etc. There is only one instance of java.lang.Runtime class is available for one java application.

The Runtime.getRuntime() method returns the singleton instance of Runtime class.

No.MethodDescription

1)public static Runtime getRuntime()returns the instance of Runtime class. 2)public void exit(int status)terminates the current virtual machine. 3)public void addShutdownHook(Thread hook)registers new hook thread. 4)public Process exec(String command)throws IOExceptionexecutes given command in a separate process. 5)public int availableProcessors()returns no. of available processors. 6)public long freeMemory()returns amount of free memory in JVM. 7)public long totalMemory()returns amount of total memory in JVM.

public class MemoryTest{

public static void main(String args[])throws Exception{

Runtime r=Runtime.getRuntime();

System.out.println("Total Memory: "+r.totalMemory());

System.out.println("Free Memory: "+r.freeMemory());

for(int i=0;i<10000;i++){

new MemoryTest();

}

System.out.println("After creating 10000 instance, Free Memory: "+r.freeMemory());

System.gc();

System.out.println("After gc(), Free Memory: "+r.freeMemory());

}

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foxlologame-blog · 7 years ago

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More About Shortest Board Game

Shortest Board Game

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nettoyersonmac · 8 years ago

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Libérer de la mémoire sur votre Mac – Utilisation de la commande de purge du terminal

La gestion de la mémoire est un aspect très important de Mac OS. Vous trouverez que votre Mac fonctionne parfois lentement, après l’avoir utilisé pendant quelques heures. Ceci est dû à la création et à la gestion de la mémoire.

Souvent, Mac OSX ne libérera pas la mémoire pendant un certain temps, ce qui fait que celle-ci a tendance à s’accumuler. Si vous avez un mac avec seulement 2/4 Go de RAM, celle-ci peut être rapidement pleine. Une fois qu’elle est pleine, votre mac sera extrêmement lent et vous verrez que les applications se bloquent plus souvent ce qui entachera vos performances système.

Il existe un moyen simple de libérer de la mémoire sans forcement avoir à redémarrer votre mac !

Utilisation du terminal

L’utilisation du terminal pour libérer de la mémoire est un procédé plutôt simple, mais il va vous falloir vous lancer dans l’apprentissage de quelques lignes de code (et oui les Mac possèdent la même architecture). Nous allons nous pencher sur le fameux command purge, qui permet de se débarrasser de toute la mémoire inactive.

Le système vous montrera 4 différents types de mémoire.

La mémoire libre est une mémoire qui n’est pas utilisée, qui peut être utilisée par les applications.

Inactive est la mémoire qui a été utilisée avant mais n’est plus utilisée.

La mémoire active est celle que vos applications utilisent actuellement.

La mémoire filaire est la mémoire système utilisée par Mac OS.

Pour nettoyer la mémoire inactive, vous pouvez ouvrir des applications -> utilitaires -> terminal.

Avertissement – Veuillez prendre vos précautions avant de faire cette manipulation car celle-ci n’est pas totalement sans risque !

Tapez la commande : purge

Ensuite, appuyez sur Entrée.

Cela devrait prendre quelques minutes, entrainant peut-être un ralentissement du système jusqu’à ce que cette opération soit terminée. Une fois celle-ci finie, votre Mac devrait fonctionner beaucoup plus doucement.

Utilisation d’un logiciel

Si vous n’aimez pas utiliser le terminal, vous avez toujours la possibilité d’utiliser un logiciel. L’une des meilleures applications que j’ai testé est FreeMemory.

Free Memory

Prix : gratuit Société: Rocky Sand Studio

Free Memory est une application gratuite sur la Mac Appstore. L’application est conçue spécifiquement pour libérer de la mémoire.

Une fois que vous téléchargez l’application :

Vous devriez voir l’utilisation de la mémoire dans la barre d’outils située en haut à droite. Si vous cliquez dessus et y accédez, vous devriez voir exactement combien de mémoire utilise votre Mac.

Si vous souhaitez libérer la mémoire vive, sélectionnez simplement vider la mémoire libre. Cela devrait durer 1 minute environ.

Si votre Mac n’a que 2 Go de RAM, je vous recommande de mettre à niveau au moins 4 Go. Pour obtenir une performance maximale. Vous verrez une énorme différence dans l’utilisation générale.

L’article Libérer de la mémoire sur votre Mac – Utilisation de la commande de purge du terminal est apparu en premier sur Nettoyer Son Mac.

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menubar-blog · 13 years ago

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Sophos Anti Virus - Because you can never be too careful! Fantastical - I use this to simplify my iCal workflow, especially for school. smcFanControl - This keeps my Mac cool during processor intensive activities. I have several preset speeds that I choose based on what I'm doing. It also boosts the fan speed by 750RPM while my Air is charging. Ejector - I use this especially on my MacBook Air to make removing my external disks simple. FreeMemory - I have this set to automatically purge my inactive RAM whenever it drops below a certain level. Keeps my Air smooth and responsive. Dropbox - Self explanatory. Also, awesome. BwanaDik - Keeps tabs on my current Wi-Fi situation. More informative than the built-in menu app. MenuPrefs - Simplifies changing the System Preferences. Growl - Apple should have done this... CloudApp - For quick sharing of small items between my Macs and friends Evernote - For jotting down stuff I want to remember Weather HD - Displays the weather in really nice HD graphics, and the menu bar app drops down a list of current temps for selected cities. Caffeine - Keeps my Mac running high. Then the standards: Keychain Access, Time Machine, Bluetooth, Battery, Wi-Fi, Volume, Date/Time, and Spotlight. (From Vincent Sanchez)

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