为什么会有不同数量的线程？

Question

我的Scala程序的一部分：

public static void main(String[] args) {
    setS(1);
    setW(-3);
    setA(78);
    setG(23);
    setY(-1005);

}

public static int getS() {
    System.out.print('s');
    return s;
}

public static void setS(int s) {
    chapter7.s = s;
}

public static int getW() {
    System.out.print('w');
    return w;
}

public static void setW(int w) {
    chapter7.w = w;
}

public static int getA() {
    System.out.print(a);
    return a;
}

public static void setA(int a) {
    chapter7.a = a;
}

public static int getG() {
    System.out.print(g);
    return g;
}

public static void setG(int g) {
    chapter7.g = g;
}

public static int getY() {
    System.out.print(y);
    return y;
}

public static void setY(int y) {
    chapter7.y = y;
}

}

我计算了日志文件中的线程数，该线程数为120。部分日志文件：

import java.util.concurrent.{ExecutorService, Executors, TimeUnit}

val genericExecutorService = Executors.newCachedThreadPool()

val scheduledExecutorService = Executors.newScheduledThreadPool(4)

val scheduledExecutorService1 = Executors.newScheduledThreadPool(1)

val scheduledExecutorService2 = Executors.newScheduledThreadPool(1)

计数日志文件中的线程：

2018-10-18 00:00:00,421 INFO  [pool-7-thread-32] xxx

我计算了Java的线程数

$ grep -r "thread" xxx.log | grep -Po '(?<=(\[)).*(?=\])' | sort | uniq -c | wc -l
120

为什么$ cat /proc/2966/status | grep Threads Threads: 1524 $ ps -eLF| grep -c java 1525 $ ps -L -o pid= -p 2966 | wc -l 1524 和1525如此不同？任何提示都欢迎。 谢谢。

Answer 1

您可以使用更好的工具来分析JVM应用程序中的线程，而不必依赖日志记录。有视觉工具，例如jmc和jconsole。如果您使用PROD机器，则可能会有jstack，而视觉工具可能不可用。

如果我正在关注JVM应用程序，

object Testing {

  def main(args: Array[String]): Unit = {

    import java.util.concurrent.{ExecutorService, Executors, TimeUnit}

    val genericExecutorService = Executors.newCachedThreadPool()

    val scheduledExecutorService = Executors.newScheduledThreadPool(4)

    val scheduledExecutorService1 = Executors.newScheduledThreadPool(1)

    val scheduledExecutorService2 = Executors.newScheduledThreadPool(1)

    genericExecutorService.execute(() => {
      println("0")
    })

    scheduledExecutorService.execute(() => {
      println("1")
    })

    scheduledExecutorService1.execute(() => {
      println("2")
    })

    scheduledExecutorService2.execute(() => {
      println("3")
    })
  }

}

我可以使用该应用程序的jstack使用proccessId 来获取线程，

$ jstack 68209 | grep thread
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.151-b12 mixed mode):
"pool-4-thread-1" #14 prio=5 os_prio=31 tid=0x00007ff1b812a800 nid=0xa503 waiting on condition [0x000070000c305000]
"pool-3-thread-1" #13 prio=5 os_prio=31 tid=0x00007ff1b812a000 nid=0xa703 waiting on condition [0x000070000c202000]
"pool-2-thread-1" #12 prio=5 os_prio=31 tid=0x00007ff1b80f9000 nid=0xa903 waiting on condition [0x000070000c0ff000]
"pool-1-thread-1" #11 prio=5 os_prio=31 tid=0x00007ff1b9869800 nid=0x5803 waiting on condition [0x000070000bffc000]
"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007ff1b9802800 nid=0x1c07 runnable 
"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007ff1b9001000 nid=0x1d03 runnable 
"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007ff1ba804800 nid=0x2b03 runnable 
"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007ff1ba805000 nid=0x5303 runnable 
"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007ff1ba805800 nid=0x5103 runnable 
"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007ff1b8810800 nid=0x2c03 runnable 
"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007ff1b981e800 nid=0x4e03 runnable 
"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007ff1b981f000 nid=0x4c03 runnable 

您也可以简单地执行jstack pid，但这会给出包括thread_state和all在内的线程的整个转储。

使用jmc可视工具

可能会有所帮助： Monitoring queue of ExecutionContextExecutor “scala.concurrent.ExecutionContext.Implicits.global”