NIO、BIO、AIO

IO Model

One 、 Sync 、 asynchronous

• Sync ： The thread initiates the request itself , To get the results （ One thread ）
• asynchronous ： The thread initiates the result itself , But don't get the results , Instead, other threads get the results and send them to this thread （ At least two threads ）

Two 、 The process of reading data

When the user thread calls channel.read or stream.read after , Will switch to the operating system kernel state to complete the real data reading , Reading is divided into two stages , Respectively ：

• Waiting for the data phase
• Copy data phase

3、 ... and 、 Synchronous blocking 、 Synchronous nonblocking 、 Synchronous multiplexing 、 Asynchronous non-blocking

• Blocking IO（ Sync ）（BIO）

  • The user thread is blocked , call read After the method , Waiting for kernel space to read data , No other operation , Can only wait for
  

• Non blocking IO（ Sync ）

  • User threads are not blocked , call read After the method , Even if kernel space does not read data , Returns the 0, The user thread loop calls read Method , It won't block , It is not blocked until the replication phase
  • The data replication phase is still blocked
  

• Multiplexing （ Sync , Single thread cooperation selector Use ）（NIO）

  • Block until the event occurs
  • Blocking occurs during both the wait phase and the copy phase （ Single channel From the perspective of , It's blocked ）
  • Multiple channel From the perspective of , It's non blocking , One channel No data in , It won't block , Can handle other channel
  

• Asynchronous non-blocking （ asynchronous IO）（AIO）

  • The user calls read After method , Kernel space returns immediately , Inform to get the user's request , After the kernel space completes the corresponding operation , The result is returned by another thread
  • After the kernel space completes the operation , The callback method will be called to return data
  • Because return immediately , therefore Asynchronous must not be blocking , So asynchronous must be non blocking
  

• Blocking IO vs Multiplexing （ All synchronous ）

  • Blocking IO, When processing one connection, you cannot process another connection , If you want to handle a new connection , You must wait until the last connection is completely processed before you can process a new connection
  • Multiplexing , One selector Can process multiple at the same time channel Events , Some channel When there is no data in , Threads do not need to wait , Can handle other things