Thread pool parameters and reasonable settings

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One 、 Thread pool 7 Big core parameters

1. corePoolSize 

             Number of core threads core threads will always survive , In time, there is no task to perform , When the number of threads is less than the number of core threads , Even if there are threads free , Thread pool will also give priority to creating new thread processing when set allowCoreThreadTimeout=true（ Default false） when , The core thread will time out to close

2. maximumPoolSize Maximum number of threads

         When the idle thread time reaches  keepAliveTime, The thread will shut down , Until the quantity equals corePoolSize

3. keepAliveTime free time

4. unit Time unit  

          It exceeds the lifetime unit of the core thread , As second 、 Ms etc. .

5. workQueue  Blocking queues

        LinkedBlockingQueue： Unbounded queue , Capacity Integer.MAX_VALUE,（FixedThreadPool and SingleThreadExecutor The number of threads in the thread pool is fixed , It's used LinkedBlockingQueue）

        SynchronousQueue： Directly submitted task queue （CachedThreadPool Is the maximum number of threads Integer.MAX_VALUE, It's using SynchronousQueue）

        ArrayBlockingQueue： Specify the queue size （corePoolSize > queue >maximumPoolSize ）

6. threadFactory  Thread factory

              You can customize the creation of Thread objects , For example, set the thread name 、 Whether it is a guardian thread, etc .

7. handler  Refusal strategy

        AbortPolicy： Termination strategy . The maximum load is exceeded 、 When performing a reject task , Will directly throw a type of RejectedExecutionException Of RuntimeException abnormal

        CallerRunsPolicy： The caller executes the policy . Over load , When executing policy , The caller thread performs the task .

        DiscardOldestPolicy： Discard the earliest task strategy . Over load , Discard the oldest task in the queue . If the route pool is closed , Give up .

        DiscardPolicy： Discard strategy . Over load , Discarding the task .

         Realization RejectedExecutionHandler Interface , Custom policy

Two 、 Reasonable setting of thread pool parameters

Ø tasks, The maximum number of tasks that the program needs to process per second

Ø tasktime, The time required for a single thread to process a task

Ø responsetime, The system allows the maximum response time for tasks

corePoolSize

Each task requires tasktime Second processing , Then each thread can process 1/tasktime A mission . The system has... Per second tasks A task needs to be handled , The number of threads required is ：tasks/(1/tasktime). namely tasks*tasktime Number of threads . The specific figures should be based on 8020 principle , namely 80% In this case, the number of system tasks per second .

queueCapacity： The length of the task queue

         The length of the task queue depends on the number of core threads , And the requirements of the system for task response time . The queue length can be set to (corePoolSize/tasktime)responsetime

maxPoolSize: Maximum number of threads

         When the system load reaches the maximum , The number of core threads has failed to complete all tasks on time , In this case, you need to add threads . Per second 200 A task requires 20 Threads , So when every second reaches 1000 A task , You need to (1000-queueCapacity)*(20/200).

keepAliveTime

        keepAliveTiime The set value can be set according to the peak duration of the task .

The above calculation of the number of threads does not consider CPU The situation of . If combined CPU The situation of , such as , When the number of threads reaches 50 when ,CPU achieve 100%, Will maxPoolSize Set to 60 It's not appropriate , At this time, if the system load is maintained at every second for a long time 1000 A mission , Then it exceeds the processing capacity of the process pool , Try to reduce the processing time of each task (tasktime).

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