Java nio to Kotlin

[daehwan2yo]

NIO

Java New Input & Output

• from JDK 4 to implement high-speed I/O operations
• alternative to the standard I/O APIs

using java nio

• Non-blocking I/O Operations
  • reads data whichever is ready
  • thread can ask a channel to read data from a buffer and thread can go for other work
  • if I/O finished, thread can continue again from the previous point
• Buffer oriented approach

Channel : I/O abstraction

• a bit like stream used for communicating with the outside world
• read data from a buffer or write from a buffer
• Channel allows java NIO non-blocking operations

Selectors : an Object which monitors multiple channels for the events

• handling multiple channels which are using single thread

기존 java io package 와 차이점

• C 와 같은 언어와 달리 JVM 위에서 동작하는 언어로, 직접 메모리를 관리하거나, os 수준의 system call 을 사용할 수 없기에, Kernel buffer (read()) 로 읽어들여온 데이터를 Process (JVM) 으로 이동시켜주는 추가적인 작업 (Context Switching 발생) 이 일어난다.
  • thread block 발생 java io package 는 stream oriented, java nio pacakge 는 buffer oriented
• java io 는 blocked working
• java nio 는 channel 에 read 요청을 보내고 channel 이 read 하며 buffer 를 채우는 동시에 thread 는 다른 작업을 수행가능하도록한다.
  • thread 가 read() 혹은 write() 를 수행을 channel 에 요청하여 thread 가 block 되어지지 않는다.

[daehwan2yo]

Buffer

A container for data of a specific primitive type

• linear
• sequencial every buffer is readable, but not every buffer is writeable.

thread safety : are not safe for use by multiple concurrent threads.

Transferring data

Each subclass of this class defines two categories of get and put operations.

Marking and resetting

mark is not always defined.

• never negative and is never greater than the position.
• buffer's mark is the index to which its position will be reset when reset method is invoked

  Invariants

  A newly-created buffer always has a position of zero and a mark that is undefined.

• initial limit may be zero or it may be some other value that depends upon the type of the buffer and the manner in which it is constructed.
• Each element of a newly-allocated buffer is initialized to zero.

  0 <= mark <= position <= limit <= capacity

Additional operations

• clear
  • makes a buffer ready for a new sequence of channel-read or relative put operations.
  • set limit to the capacity and the position to zero
• flip
  • makes a buffer ready for a new sequence of channel-write or relative get operations
  • set limit to the capacity and the position to zero
• rewind
  • makes a buffer ready for re-reading the data that is already contains
• slicce
  • create subsequence of a buffer
• duplicate
  • create a shallow copy of a buffer