DirectMemory

PooledUnsafeDirectByteBuf not found in DirectMemory

由 你说的曾经没有我的故事 提交于 2019-12-24 23:30:03
问题 I am using Netty 4.1.17-Final. I wrote the code to send and receive 100 MB random ASCII. Decoder does not read until ByteBuf becomes 100 MB. @Override public void decode(ByteBuffer _in, List<Object> _out) { if (_in.remaining() == size) { // size = 100 * 1024 * 1024 _in.get(new byte[size]); } } Therefore, Netty buffers 100 MB, but it was not found even by monitoring Direct Memory. System.out.println(sun.misc.SharedSecrets.getJavaNioAccess().getDirectBufferPool().getMemoryUsed());

Using DMA to access High Speed Serial Port

由 ￣綄美尐妖づ 提交于 2019-12-12 12:23:15
问题 I use serialport component in c# and it works well! But the question is how can it be faster to handle high speed (e.g. 2 Mbps) data transfers. As I have researched about this, I have found that memory can be accessed directly (using DMA like this link ). Can anybody tell me how can I define and use it in my application? 回答1: No, the [c#] tag puts this a million miles out of reach. The code snippet on that web page is not real, it is just a "pattern". It does things you cannot do in C#, like

How to free memory using Java Unsafe, using a Java reference?

由 怎甘沉沦 提交于 2019-12-12 08:55:32
问题 Java Unsafe class allows you to allocate memory for an object as follows, but using this method how would you free up the memory allocated when finished, as it does not provide the memory address... Field f = Unsafe.class.getDeclaredField("theUnsafe"); //Internal reference f.setAccessible(true); Unsafe unsafe = (Unsafe) f.get(null); //This creates an instance of player class without any initialization Player p = (Player) unsafe.allocateInstance(Player.class); Is there a way of accessing the

JAVA NIO之浅谈内存映射文件原理与DirectMemory

由 梦想与她 提交于 2019-11-27 17:26:21
JAVA类库中的NIO包相对于IO 包来说有一个新功能是内存映射文件，日常编程中并不是经常用到，但是在处理大文件时是比较理想的提高效率的手段。本文我主要想结合操作系统中（OS）相关方面的知识介绍一下原理。 在传统的文件IO操作中，我们都是调用操作系统提供的底层标准IO系统调用函数 read()、write() ，此时调用此函数的进程（在JAVA中即java进程）由当前的用户态切换到内核态，然后OS的内核代码负责将相应的文件数据读取到内核的IO缓冲区，然后再把数据从内核IO缓冲区拷贝到进程的私有地址空间中去，这样便完成了一次IO操作。至于为什么要多此一举搞一个内核IO缓冲区把原本只需一次拷贝数据的事情搞成需要2次数据拷贝呢？ 我想学过操作系统或者计算机系统结构的人都知道，这么做是为了减少磁盘的IO操作，为了提高性能而考虑的，因为我们的程序访问一般都带有局部性，也就是所谓的局部性原理，在这里主要是指的空间局部性，即我们访问了文件的某一段数据，那么接下去很可能还会访问接下去的一段数据，由于磁盘IO操作的速度比直接访问内存慢了好几个数量级，所以OS根据局部性原理会在一次 read()系统调用过程中预读更多的文件数据缓存在内核IO缓冲区中，当继续访问的文件数据在缓冲区中时便直接拷贝数据到进程私有空间，避免了再次的低效率磁盘IO操作。在JAVA中当我们采用IO包下的文件操作流，如： [java
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