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Java New I/O
http://www.ronsoft.com
Java NIO Book Websitehttp://javanio.info
Java Metroplex User's GroupMay 14, 2003
© 2003, Ronsoft Technologies
Pig-Footed Bandicoot
See http://javanio.info for details
Check Your Local Bookstore
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Speaker Bio25+ Years Computer Experience
Mainframe to Micro
Unix/Linux kernel, academic, internet ~20 years
5+ Years Java ExperienceHeavy server-side, web apps, startups
Independent Consultant“Bit twiddling at it's finest”
Will hack NIO for fun and profit
Hook ‘Em Horns
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Why NIO?
Where did it come from?
What does it do for me?
When should I use it?
Should I stop using java.io?
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Efficiency – Scalability – Reliability
Efficiency – The Need For SpeedWhy should the JVM do what the OS can do better?
Scalability – Livin' LargeBig applications have big appetites
Reliability – Enough Wheels InventedThe infrastructure exists – concentrate on the app
No Longer CPU BoundJSR 51 (http://www.jcp.org/en/jsr/detail?id=51)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
What Does NIO Do For Me?
New AbstractionsBuffers, Channels and Selectors
New CapabilitiesNon-Blocking Sockets
File Locking
Memory Mapping
Readiness Selection
Regular Expressions
Pluggable Charset Transcoders
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Use NIO When You Need To:
Move large amounts of data efficientlyNIO is primarily block oriented – java.io uses streams
Uses direct buffers to do raw I/O – bypassing the JVM
Multiplex large numbers of open socketsOperates in non-blocking mode
One thread can manage huge numbers of socket channels
Use OS-level file locking or memory mapping
Do character set Transcoding
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Should I Stop Using java.io?
Nope
java.nio is not a replacement for java.io
NIO addresses different needs
java.io is not going away
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
What Makes Up NIO?
Buffers
Channels
Selectors
Regular Expressions
Character Set Coding
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
NIO Buffers
Fixed size containers of primitive data typesByteBuffer, CharBuffer, FloatBuffer, etc.
Byte buffers are special, used for I/O with channels
Direct and Non-direct ByteBuffersDirect ByteBuffers address raw memory – direct I/O
Buffers can be views of other buffers or wrap arrays
Byte order (endian-ness)Affects byte swabbing in views of ByteBuffers
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Buffer Classes
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Buffer Objects (Empty/Fill)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Buffer Objects (Flip)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Buffer Views (Dupe/Slice)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Buffer Views (Char View)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
I'm Confused...Show Me
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Hello?
public class HelloWorld{
public static void main (String [] argv){
System.out.println ("Hello World");}
}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Hello NIO?
import java.nio.ByteBuffer;import java.nio.channels.WritableByteChannel;import java.nio.channels.Channels;
public class HelloWorldNio{
public static void main (String [] argv)throws Exception
{String hello = "Hello World" + System.getProperty ("line.separator");ByteBuffer bb = ByteBuffer.wrap (hello.getBytes ("UTF-8"));WritableByteChannel wbc = Channels.newChannel (System.out);
wbc.write (bb);wbc.close();
}}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
NIO Channels
New I/O metaphor: Conduit to an I/O service (“nexus”)
Channels do bulk data transfers to and from bufferschannel.write (buffer) ~= buffer.get (byteArray)channel.read (buffer) ~= buffer.put (byteArray)
Scatter/gather, channel-to-channel transfers
Three primary channel implementationsFileChannel: File locks, memory mapping, cross-connect transfers
Sockets: Non-blocking, selectable, async connections, peers
Pipe: loopback channel pair, selectable, generic channels
Selectable Channel Implementations are pluggable (SPI)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Channel Copy – Simple #1*
public void channelCopy (ReadableByteChannel src, WritableByteChannel dest)throws IOException
{ByteBuffer buffer = ByteBuffer.allocate (16 * 1024);
while (src.read (buffer) != -1) {// prepare the buffer to be drainedbuffer.flip();
// make sure the buffer was fully drained.while (buffer.hasRemaining()) {
dest.write (buffer);}
// make the buffer empty, ready for fillingbuffer.clear();
}}
* No buffer copies, but potentially more system calls.
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Channel Copy – Simple #2*
public void channelCopy (ReadableByteChannel src, WritableByteChannel dest)throws IOException
{ByteBuffer buffer = ByteBuffer.allocate (16 * 1024);
while (src.read (buffer) != -1) {// prepare the buffer to be drainedbuffer.flip();
// write to the channel, may blockdest.write (buffer);
// if partial transfer, shift remaining elements down// if buffer was empty, same as doing clearbuffer.compact();
}
buffer.flip(); // EOF leaves buffer in fill state
while (buffer.hasRemaining()) {dest.write (buffer);
}}
* Minimal system calls, but may do buffer copies. Post loop cleanup needed.
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Channel Copy – Transfer*
public void channelCopy (FileChannel src, WritableByteChannel dest)throws IOException
{src.transferTo (0, src.size(), dest);
}
public void channelCopy (ReadableByteChannel src, FileChannel dest)throws IOException
{dest.transferFrom (src, 0, Long.MAX_VALUE);
}
* Very easy, but one end must always be a FileChannel. Transfer could occur entirely in kernel space.
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Memory Mapped Buffers
RandomAccessFile raf = new RandomAccessFile (fileName, "rw");FileChannel fc = raf.getChannel();MappedByteBuffer buffer = fc.map (FileChannel.MapMode.READ_WRITE, 0, fc.size());
byte b = buffer.get(); // reads from file...buffer.put (someOtherByte); // writes to file
The content of buffer is the content of fileNameAny change to one affects the other
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Non-Blocking Sockets – Simple Really
ByteBuffer buffer = ByteBuffer.allocate (1024);SocketChannel socketChannel = SocketChannel.open();socketChannel.configureBlocking (false);
...
while (true) { ... if (socketChannel.read (buffer) != 0) { processInput (buffer); } ...}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Non-Blocking Server Socket
ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.socket().bind (new InetSocketAddress (port));ssc.configureBlocking (false);
while (true) {SocketChannel newConnection = ssc.accept();
if (newConnection == null) {doSomethingToKeepBusy();
} else {doSomethingWithSocket (newConnection);
}}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
NIO Selectors
Multiplexing Channels – Readiness Selection
Selectable Channels are registered with SelectorsSelectionKey encapsulates selector/channel relationship
A subset of ready channels is selected from the Selector's set of registered channels (Selector.select())
Selected Set contains those keys with non-empty Ready Sets
Each SelectionKey holds an Interest Set and a Ready SetPossible members of Interest Set: accept, read, write, connect
Ready set is a subset of interest set –as-of the last select() call
Readiness Selection means less work – ignore idle channels
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Selectors, Keys and Channels
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Registering With a Selector
ServerSocketChannel serverChannel = ServerSocketChannel.open();Selector selector = Selector.open();
serverChannel.socket().bind (new InetSocketAddress (port));serverChannel.configureBlocking (false);serverChannel.register (selector, SelectionKey.OP_ACCEPT);
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
The Selection Process
Create a Selector and register channels with itThe register() method is on SelectableChannel, not Selector
Invoke select() on the Selector object
Retrieve the Selected Set of keys from the SelectorSelected set: Registered keys with non-empty Ready Sets
keys = selector.selectedKeys()
Iterate over the Selected SetCheck each key's Ready Set (set of operations ready to go as-of last select())
Remove the key from the Selected Set (iterator.remove())Bits in the Ready Sets are never reset while the key is in the Selected Set
The Selector never removes keys from the Selected Set – you must do so
Service the channel (key.channel()) as appropriate (read, write, etc)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Running a Selection Loopwhile (true) { selector.select();
Iterator it = selector.selectedKeys().iterator();
while (it.hasNext()) { SelectionKey key = (SelectionKey) it.next();
it.remove();
if (key.isAcceptable()) { ServerSocketChannel server = (ServerSocketChannel) key.channel(); SocketChannel channel = server.accept(); channel.configureBlocking (false); channel.register (selector, SelectionKey.OP_READ); }
if (key.isReadable()) readDataFromSocket (key); }}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Scalability With Selectors
One Thread to Rule Them AllMore threads != More Efficient – Context Switching, CPU Availability
OS and/or JVM do the hard work for youOnly the kernel can efficiently do Readiness Selection
No more thread-per-socket nonsenseSimpler, easier to maintain code
Less concurrency hassles – locking overhead, thread races
Single point of dispatch
Not necessarily single-threadedSingle selection thread can dispatch to multiple worker threads
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
How Does That Work...Exactly?
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
NIO Regular Expressions
Perl 5-ish syntax
New CharSequence interface in java.lang
Pattern and Matcher objects
String class has regex convenience methods added
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
java.lang.CharSequence
Package java.lang;
public interface CharSequence{ int length(); char charAt(int index); CharSequence subSequence(int start, int end); public String toString();}
Implemented by String, StringBuffer and CharBuffer
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Regex CSV Tokenizer
String [] tokens = lineBuffer.split ("\\s*,\\s*");
for (int i = 0; i < tokens.length; i++) {System.out.println ("" + i + ": " + tokens [i]);
}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
Regex Email Address Parsingpublic static final String VALID_EMAIL_PATTERN =
"([a-zA-Z0-9_\\-\\.]+)@((\\[[0-9]{1,3}\\.[0-9]"+ "{1,3}\\.[0-9]{1,3}\\.)|(([a-zA-Z0-9\\-]+\\.)+))"+ "([a-zA-Z]{2,4}|[0-9]{1,3})(\\]?)";
...
public void setupPerson (Person person, ..., String emailAddress){
...if (emailAddress.matches (VALID_EMAIL_PATTERN)) { person.setEmailAddress (emailAddress);} else { throw new IllegalArgumentException (emailAddress);}...
}
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
NIO Charsets
Character Set Coding
Character Set, Coded Character Set, Coding Scheme
Encoding and decoding objects
Character sets are pluggable (SPI)
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
The JNI ConnectionJava Code Can Allocate Native Memory (Direct)
Native Code Can Create and/or Use Buffers
Buffers Can Wrap Arbitrary Memory SpacesVideo memory, device controllers, etc.
All Buffers Are Java ObjectsScoping, Garbage Collection, Typing, Etc.
Zoom ZoomOpenGL For Java (http://www.jausoft.com)
JCanyon F16 Flight Simulator
Ronsoft Technologieshttp://javanio.info
http://www.ronsoft.com
What Did They Leave Out?
Formatted I/O (ala printf/scanf)Will leverage Regular Expressions
Enhanced Filesystem InterfaceMore consistent across OS platforms
Better access to file/directory attributes
Pluggable access to new filesystem types
True Asynchronous I/OUnder consideration, may never happen
Questions
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???
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Bye ByeBuy my Daddy's book. I think I see one right over there.
Ron (and Miranda) Hitchens [email protected]
http://www.ronsoft.com http://javanio.info