memory | 易学教程

Understanding memcpy

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问题 int a = 10; int* pA = &a; long long b = 200; long long* pB = &b; memcpy (pB,pA,4); memcpy (pB+1,pA,4); cout<<"I'm a memcpy!: "<<*(pB)<<endl; I'm doing some tests with memcpy to teach myself how memory works. What I am trying to do is make b = to "1010". I can copy the value from a to b, but then I try to offset the memory by 1 byte and write another 10 but it doesn't work it only outputs "10". What would I need to do to get a value of 1010? 回答1: A few problems with your code as it stands: You

Why “Allowed memory size exhausted”?

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问题 I am writing a batch script and get a Allowed memory size of 134217728 bytes exhausted error. I don't understand why the memory is filling up. I tried unsetting the $row variable, but that didn't change a thing. Here is my code: // ... (sql connection) $result = mysql_query("SELECT * FROM large_table"); while ($row = mysql_fetch_array($result)) { echo $row['id'] . PHP_EOL; unset($row); } (simplified code) Why does the memory fill up, and how can I avoid it? Note: this is a batch script. This

Memory usage of constructors in haskell [duplicate]

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问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Memory footprint of Haskell data types When solving combinatorial problems, I will often represent the solution as a bit string, eg. 1010100010110111000110... You get the picture. I figured that when I use [Int] for the bit string, Int always spends the same amount of memory, no matter how big the number actually is (because Int it's bounded, in contrast to Integer ), as the computer only remembers the bit

What could cause this memory issue?

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问题 I'm working on an app for windows phone 8, and I'm having a memory leak problem. But first some background. The app works (unfortunately) using WebBrowsers as pages. The pages are pretty complex with a lot of javascript involved. The native part of the app, written in c#, is responsible for doing some simple communication with the javascript(e.g. native is a delegate for the javascript to communicate with a server), make animation for page transition, tracking, persistance, etc. All is done

Spark调优指南

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Spark相关问题 Spark 比 MR 快的原因？ 1) Spark 的计算结果可以放入内存，支持基于内存的迭代， MR 不支持。 2) Spark 有 DAG 有向无环图，可以实现 pipeline 的计算模式。 3) 资源调度模式： Spark 粗粒度资源调度， MR 是细粒度资源调度。资源复用： Spark 中的 task 可以复用同一批 Executor 的资源。 MR 里面每一个 map task 对应一个 jvm ，不能复用资源。 Spark 中主要进程的作用？ Driver 进程：负责任务的分发和结果的回收。 Executor 进程：负责具体任务的执行。 Master 进程： Spark 资源管理的主进程，负责资源调度。 Worker 进程： Spark 资源管理的从进程， woker 节点主要运行 Executor Spark调优 1. 资源调优 1) .搭建Spark集群的时候要给Spark集群足够的资源（core，memory）在 spark安装包的conf下spark-env.sh SPARK_WORKER_CORES SPARK_WORKER_MEMORY SPARK_WORKER_INSTANCE 2) .在提交Application的时候给Application分配更多的资源。提交命令选项：（在提交 Application的时候使用选项） -

node.js process out of memory error

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问题 FATAL ERROR: CALL_AND_RETRY_2 Allocation Failed - process out of memory I'm seeing this error and not quite sure where it's coming from. The project I'm working on has this basic workflow: Receive XML post from another source Parse the XML using xml2js Extract the required information from the newly created JSON object and create a new object. Send that object to connected clients (using socket.io) Node Modules in use are: xml2js socket.io choreographer mysql When I receive an XML packet the

R memory not released in Windows

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问题 I am using RStudio in Windows 7 and I have a problem in releasing memory to the OS. Below is my code. In a for loop: I read data through an API call of the Census.gov website and I use the package acs to save them in a .csv file via the temporary object table . I remove the table (usual size: few MB), and I use the package pryr to check memory usage. According to the function mem_used() , after the removal of table , R always returns to a constant memory usage; instead according to Windows

Does “readonly” (C#) reduce memory usage?

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问题 In C#, does setting a field as readonly reduce memory usage? i.e. DBRepository _db = new DBRepository(); vs readonly DBRepository _db = new DBRepository(); Just curious. Thanks. 回答1: No. It means you can't assign to it except at the declaration point or in a constructor. You also can't pass it as a ref or out parameter to a method. Edit: based on the comment below. The following field is readonly because you want callers to have direct read access to string.Empty , but you don't want them to

best way to load an image library of iphone nsmutablearray (600+ items)

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问题 I have created an app which has a library of images. I have imported the images in to my resources folder in Xcode and am currently loading them in to an array in the appDelegate when the app loads. This is happening each time. I am now worried that as the library grows the app will run out of memory. Is there a better way of loading these? the structure is Library > category > image list > image I have an NSMutableArray called mainLibrary which I then add another nsmutablearray for each

Check how much memory my program uses

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问题 I have a C-code program running in my computer and I need to check how much memory my program uses when it is running. Is there any tool that I can use? PS: Does massif tool ( valgrind ) work in this case? I already ran it but I don't know how to interpret the graphic created by it. PPS: I'm using Linux (eOs). 回答1: Massif is a great tool that displays how much memory your program uses over time. It has some drawbacks, though: All Valgrind tools are slow; if your program is slow, Massif will