My colleagues went to listen to Ali last week openJDK The lecture of , Collected and sorted out . With Oracle Let go ,Java 8 Official support lasts until 2020 year 12 month ; For business users (Commercial Users),2019 year 1 No more free updates after 12 months .

Huawei openJDK characteristic

This paper mainly explains the concept of optimization between coprocesses , And performance optimization

Ali openJDK characteristic (Alibaba Dragonwell 8 )

1. Control the upstream Java 11 Of Java Flight Recorder (JFR) function .

2. Integrate JWarmup technology ( Preheating function )

3. Provide GC Problem diagnosis, etc Serviceability Improvement in the quality of life .

I organized my knowledge notes :

1、 process

A process is a program with some independent functions. It is a running activity on a data set , A process is an independent unit of the system for resource allocation and scheduling . Each process has its own independent memory space , Different processes communicate through inter process communication . Because the process is heavier , Occupy independent memory , So the switching overhead between context processes ( Stack 、 register 、 Virtual memory 、 File handle, etc ) The larger , But relatively stable and safe .

2、 Threads

A thread is an entity of a process , yes CPU Basic unit of dispatch and dispatch , It's a smaller, independent, basic unit than a process . The thread itself basically does not have system resources , Have only a few essential resources in operation ( Such as program counter , A set of registers and stacks ), But it can share all the resources owned by a process with other threads belonging to the same process . Communication between threads is mainly through shared memory , Context switching is fast , Less resource overhead , But it's easier to lose data than it's unstable .

3、 coroutines ( User mode thread is called coroutine for short )

Coroutine is a lightweight thread in user mode , The scheduling of the process is completely controlled by the user . It has its own register context and stack . When the coordination scheduling is switched , Save register context and stack elsewhere , At the time of cutting back , Restore the previously saved register context and stack , The direct operation stack basically has no kernel switching overhead , You can access global variables without locking , So context switching is very fast .

  • If the clock is blocked 、 We don't need thread switching any more , I write a logical flow scheduling thing in the process . Then we can take advantage of concurrency , It can also avoid repeated system calls , And the overhead of process switching , It's easy to give you thousands of logic streams every minute . This is it. User thread .
  • You can see from above , To implement a user mode thread, there are two problems that must be dealt with : One is blocking I\O Will cause the whole process to hang ; Second, due to the lack of clock blocking , Processes need to have their own ability to schedule threads . If an implementation requires each thread to call a method itself , Take the initiative to hand over control . So we call this user mode thread Collaborative , That is coroutines .

http://www.zhihu.com/question/20511233

4、Daemon
Daemon() The program is the server that runs all the time Program , Also known as Daemon . It usually runs in the background of the system , There is no control terminal , No interaction with the front desk ,Daemon Programs are generally used as system service send use .Daemon It's a long-running process , It usually runs after the system starts , It ends when the system is shut down . In general Daemon The program runs in the background , Because it has no control terminal , I can't talk to you The user interaction of the platform .Daemon Programs are generally used as service programs , Waiting for the client program to communicate with it . We also put the running Daemon Programs are called daemons .
 
5. Multi tenant concept
Multi tenant technology can share system instances among multiple tenants , At the same time, it can realize the personalized customization of the tenant's system instance . By using multi tenant technology, the common parts of the system can be shared , The parts of personality are isolated . By reusing resources among multiple tenants , Operation management and maintenance resources , Effectively save the cost of development and application . and , Sharing a single instance of the application between tenants , When the application is upgraded , All tenants can upgrade at the same time . meanwhile , Because multiple tenants share the core code of the system , So when the system upgrades , Just upgrade the same core code .

6.Wisp coroutines

Alicoprocess optimization .

7.ZenGC

A customized version of Alibaba's big data scenario ZenGC (G1 based) Release

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