memory-mapped-files

Memory-mapped files and low-memory scenarios

由 ↘锁芯ラ 提交于 2019-11-28 04:39:56
How does the iOS platform handle memory-mapped files during low-memory scenarios? By low-memory scenarios, I mean when the OS sends the UIApplicationDidReceiveMemoryWarningNotification notification to all observers in the application. Our files are mapped into memory using +[NSData dataWithContentsOfMappedFile:] , the documentation for which states: A mapped file uses virtual memory techniques to avoid copying pages of the file into memory until they are actually needed. Does this mean that the OS will also unmap the pages when they're no longer in use? Is it possible to mark pages as being no

MemoryMappedFile doesn't work with 2 processes?

由 十年热恋 提交于 2019-11-28 02:03:38
问题 I've made a simple test with a MemoryMappedFile as msdn says : 2 processes, 1 memory mapped file : the first process adds the string "1" the first process waits the second process adds the string "2" and terminates the first process now reads the whole memory mapped file process A: using (MemoryMappedFile mmf = MemoryMappedFile.CreateNew("testmap", 10000)) { bool mutexCreated; Mutex mutex = new Mutex(true, "testmapmutex", out mutexCreated); using (MemoryMappedViewStream stream = mmf

Using boost::iostreams::mapped_file_source with std::multimap

由 本小妞迷上赌 提交于 2019-11-27 15:54:44
I have a rather large amount of data to analyse - each file is about 5gigs. Each file is of the following format: xxxxx yyyyy Both key and value can repeat, but the keys are sorted in increasing order. I'm trying to use a memory mapped file for this purpose and then find the required keys and work with them. This is what I've written: if (data_file != "") { clock_start = clock(); data_file_mapped.open(data_file); data_multimap = (std::multimap<double, unsigned int> *)data_file_mapped.data(); if (data_multimap != NULL) { std::multimap<double, unsigned int>::iterator it = data_multimap->find

How does mmap improve file reading speed?

由 白昼怎懂夜的黑 提交于 2019-11-27 14:52:58
Assuming the address space can cover the file, it appears to me that mmap simply allocates a chunk of memory as large as the file about to be read, and creates a 1-to-1 relation between their corresponding blocks. However, why doing so speeds up file reading? It seems that in order to actually get the contents of the file, you still have to go to the disk, and read all the bytes on it. What difference does it make, compared to malloc'ing the same size of memory and manually read the entire file into the malloc'ed area? Craig Estey mmap works differently. It is anticipatory and adapts to the

How can I quickly read bytes from a memory mapped file in .NET?

由 戏子无情 提交于 2019-11-27 11:39:40
问题 In some situations the MemoryMappedViewAccessor class just doesn't cut it for reading bytes efficiently; the best we get is the generic ReadArray<byte> which it the route for all structs and involves several unnecessary steps when you just need bytes. It's possible to use a MemoryMappedViewStream , but because it's based on a Stream you need to seek to the correct position first, and then the read operation itself has many more unnecessary steps. Is there a quick, high-performance way to read

Memory Mapped Files .NET

由 ぐ巨炮叔叔 提交于 2019-11-27 08:41:35
I have a project and it needs to access a large amount of proprietary data in ASP.NET. This was done on the Linux/PHP by loading the data in shared memory. I was wondering if trying to use Memory Mapped Files would be the way to go, or if there is a better way with better .NET support. I was thinking of using the Data Cache but not sure of all the pitfalls of size of data being saved in the Cache. I know this is a bit late, but the .NET 4.0 framework now supports memory-mapped files out of the box: http://blogs.msdn.com/salvapatuel/archive/2009/06/08/working-with-memory-mapped-files-in-net-4

Storing vector in memory mapped file

由 半腔热情 提交于 2019-11-27 07:15:59
问题 I am attempting to store a vector of arbitrary elements in a memory mapped file (for now I'm trying to succeed with a vector of ints but it should work with vector of arbitrary objects). I have found plenty of documentation on doing so with shared memory, but not with memory mapped files proper. Since I have successfully made and used R-trees in memory mapped file (like in that example), I tried to replicate the process with vectors, but I guess I am missing some crucial element because it

Simplest way to read a CSV file mapped to memory?

由 不羁岁月 提交于 2019-11-27 07:15:07
问题 When I read from files in C++(11) I map them in to memory using: boost::interprocess::file_mapping* fm = new file_mapping(path, boost::interprocess::read_only); boost::interprocess::mapped_region* region = new mapped_region(*fm, boost::interprocess::read_only); char* bytes = static_cast<char*>(region->get_address()); Which is fine when I wish to read byte by byte extremely fast. However, I have created a csv file which I would like to map to memory, read each line and split each line on the

When to use memory-mapped files?

由 白昼怎懂夜的黑 提交于 2019-11-27 05:35:09
问题 I have an application that receives chunks of data over the network, and writes these to disk. Once all chunks have been received, they can be decoded/recombined into the single file they actually represent. I'm wondering if it's useful to use memory-mapped files or not - first for writing the single chunks to disk, second for the single file into which all of them are decoded. My own feeling is that it might be useful for the second case only, anyone got some ideas on this? Edit: It's a C#

Memory-mapped files and low-memory scenarios

由 两盒软妹~` 提交于 2019-11-27 05:24:32
问题 How does the iOS platform handle memory-mapped files during low-memory scenarios? By low-memory scenarios, I mean when the OS sends the UIApplicationDidReceiveMemoryWarningNotification notification to all observers in the application. Our files are mapped into memory using +[NSData dataWithContentsOfMappedFile:], the documentation for which states: A mapped file uses virtual memory techniques to avoid copying pages of the file into memory until they are actually needed. Does this mean that
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