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From: Jan Burse <janburse@fastmail.fm>
Newsgroups: comp.lang.java.programmer
Subject: Re: Fav. Memory Stream Impl.
Date: Sat, 28 Jan 2012 00:11:13 +0100
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Roedy Green schrieb:
> On Fri, 25 Nov 2011 18:39:23 +0100, Jan Burse<janburse@fastmail.fm>
> wrote, quoted or indirectly quoted someone who said :
>
>> Would be interested in a good memory stream
>> implementation. Requirement will be multiple
>> readers / writers and positioning.
>
> What do you use it for?  What does it do for you?
> Is it just an ram-resident InputStream?

Dear All,

I found an interesting implementation. On linux
level there is ashmem for Android. And then on Java
level there is an implementation of a class called
MemoryFile. The memory file acts as a factory for
input/output streams:

 
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/2.2_r1.1/android/os/MemoryFile.java#MemoryFile

     public InputStream getInputStream() {
         return new MemoryInputStream();
     }

     public OutputStream getOutputStream() {
         return new MemoryOutputStream();
     }

The above two streams account for sequential access,
and via mark/release some pseudo random access.
But there is also an api for random access. Namely
the following two beasts:

     public int  readBytes(byte[] buffer, int srcOffset,
          int destOffset, int count);

     public void writeBytes(byte[] buffer, int srcOffset,
         int destOffset, int count)

Compare to a normal read/write there is an additional
parameter for the offset inside the memory file. But
the implementation is not really light weight. Namely
the memory file can shared accross processes, which
I do not need:

     http://elinux.org/Android_Kernel_Features#ashmem

But at least it gives an idea how to bootstrap a
memory file implementation. Namely the input/output
streams are implemented based on the read/write with
the extra argument. Makes for examples mark/release
quite simple....

Cool!

Bye