5 modes of IO model

Reference resources ：unix Network programming
Preface ：

stay LInux Under the system , User space and kernel space can be switched to each other

Blocking IO

Blocking IO： Switch from user space to kernel space , Kernel space is waiting for data to arrive , When the data arrives, it is copied from the network card to the memory , After copying, switch from kernel space to user space , Read . During this process, the user thread has been blocked .（ Handling one event cannot handle other events ）

Synchronous blocking

Non blocking IO

Non blocking IO： Wait until the data is not blocked , Data is also blocked when it reaches the replication phase .

Synchronous nonblocking

Multiplexing

selector, Stop it first , If something happens, it won't be blocked ;read Also block . It saves time waiting for events .

The essence is also synchronization

Signal driven

asynchronous IO

Threads 1 launch （ Specify the callback method ） -----> Threads 2 To get the results （ After the result comes out, it passes through the thread 1 Method return ）
Asynchronism is non blocking .

Sync ： The thread initiates the action itself , Get the results yourself .
asynchronous ： Thread initiated action , Other threads get results .

Read file write socket flow

java Use direct memory , There is no need to copy between the user buffer and the kernel buffer , in total 3 Time , save 1 Time .

Optimize

linux2.1 Provided sendFile Method ,java Corresponding channel Of transferTo and transFrom Method copy

linux2.4 java Called transferTo After the method , from java From user mode to kernel mode , Use DMA Read data into kernel buffer , Can't use cpu,
Only the user mode and kernel mode are switched , Data from disk to kernel buffer , From the kernel buffer to the network card ,0 Copying is not done java Of memory , Will not occupy cpu Time .DMP Will liberate cpu Time .
0 Copy is suitable for small file transfer .