【java】最小话线程池ThreadPoolExecutor方法

参考文章：
阿里一面：那我把线程池coreSize配置成0会怎样？

方法解释：
getPoolSize：Returns the current number of threads in the pool.
getActiveCount：Returns the approximate number of threads that are actively executing tasks.

import org.scalatest.funsuite.AnyFunSuite
import java.util.concurrent.{ArrayBlockingQueue, Executors, ThreadPoolExecutor, TimeUnit}

class TreadPoolCreationTest extends AnyFunSuite {

  test("ts") {
    val start = System.currentTimeMillis()
    // val pool:ThreadPoolExecutor=getEmptyPool()
    val pool:ThreadPoolExecutor=getFixxedPool()
    val end = System.currentTimeMillis()
    println(f"elapsed ${(end - start).toDouble / 1000}%.2f")

    printPool(pool, 3)
    println("$$$$$$$$$$$$$")
    pool.execute(new Runnable {
      override def run(): Unit = {
        Thread.sleep(3 * 1000)
      }
    })
    printPool(pool, 10)
    pool.shutdown()
  }

  def getEmptyPool():ThreadPoolExecutor={
    val pool = new ThreadPoolExecutor(
      0,
      4,
      2,
      TimeUnit.SECONDS,
      new ArrayBlockingQueue(4),
      Executors.defaultThreadFactory(),
      new ThreadPoolExecutor.DiscardPolicy()
    )
    pool
  }
  def getFixxedPool():ThreadPoolExecutor={
    val pool = new ThreadPoolExecutor(
      2,
      4,
      2,
      TimeUnit.SECONDS,
      new ArrayBlockingQueue(4),
      Executors.defaultThreadFactory(),
      new ThreadPoolExecutor.DiscardPolicy()
    )
    pool.allowCoreThreadTimeOut(true)
    pool
  }

  def printPool(pool: ThreadPoolExecutor, elapse: Int): Unit = {
    var curr: Int = 0
    while (curr < elapse) {
      println(
        s"pool size: ${pool.getPoolSize},core pool size: ${pool.getCorePoolSize}, active pool size: ${pool.getActiveCount}, allow core thread timeout: ${pool.allowsCoreThreadTimeOut()}, maximum pool size: ${pool.getMaximumPoolSize}".stripMargin)
      curr += 1
      Thread.sleep(1000)
    }
  }
}

getEmptyPool方法：

elapsed 0.00
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
$$$$$$$$$$$$$
pool size: 1,core pool size: 0, active pool size: 1, allow core thread timeout: false, maximum pool size: 4
pool size: 1,core pool size: 0, active pool size: 1, allow core thread timeout: false, maximum pool size: 4
pool size: 1,core pool size: 0, active pool size: 1, allow core thread timeout: false, maximum pool size: 4
pool size: 1,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 1,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 0, active pool size: 0, allow core thread timeout: false, maximum pool size: 4

getFixxedPool方法：

elapsed 0.00
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
$$$$$$$$$$$$$
pool size: 1,core pool size: 2, active pool size: 1, allow core thread timeout: true, maximum pool size: 4
pool size: 1,core pool size: 2, active pool size: 1, allow core thread timeout: true, maximum pool size: 4
pool size: 1,core pool size: 2, active pool size: 1, allow core thread timeout: true, maximum pool size: 4
pool size: 1,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 1,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 1,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: true, maximum pool size: 4

看看shutdown之后的变化：

  test("sd"){
    val pool = new ThreadPoolExecutor(
      2,
      4,
      100,
      TimeUnit.SECONDS,
      new ArrayBlockingQueue(4),
      Executors.defaultThreadFactory(),
      new ThreadPoolExecutor.DiscardPolicy()
    )
    printPool(pool,1)
    pool.execute(new Runnable {
      override def run(): Unit = {
        Thread.sleep(3000)
      }
    })
    pool.execute(new Runnable {
      override def run(): Unit = {
        Thread.sleep(3000)
      }
    })
    println("after execute")
    printPool(pool,1)
    pool.shutdown()
    println("after shutdown")
    printPool(pool,10)
  }

pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
after execute
pool size: 2,core pool size: 2, active pool size: 2, allow core thread timeout: false, maximum pool size: 4
after shutdown
pool size: 2,core pool size: 2, active pool size: 2, allow core thread timeout: false, maximum pool size: 4
pool size: 2,core pool size: 2, active pool size: 2, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4
pool size: 0,core pool size: 2, active pool size: 0, allow core thread timeout: false, maximum pool size: 4