How to get the number of threads in a Java process

Question

How can I see the number of threads in a Java process

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There is a static method on the Thread Class that will return the number of active threads controlled by the JVM   Thread activeCount       Returns the number of active threads in the current thread s thread group    Additionally  external debuggers should list all active threads  and allow you to suspend any number of them  if you wish to monitor them in real-time

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Generic solution that doesn t require a GUI like jconsole  doesn t work on remote terminals   ps works for non-java processes  doesn t require a JVM installed    ps -o nlwp  lt pid gt

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Useful tool for debugging java programs  it gives the number of threads and other relevant info on them   jconsole  lt process-id gt

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public class MainClass            public static void main String args                 Thread t   Thread currentThread              t setName  My Thread               t setPriority 1              System out println  current thread      t              int active   Thread activeCount              System out println  currently active threads      active             Thread all     new Thread active             Thread enumerate all              for  int i   0  i  lt  active  i                   System out println i          all i

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java lang Thread activeCount     It will return the number of active threads in the current thread s thread group   docs  http   docs oracle com javase 7 docs api java lang Thread html activeCount

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I have written a program to iterate all Threads created and printing getState   of each Thread  import java util Set   public class ThreadStatus       public static void main String args    throws Exception          for   int i 0  i lt  5  i                 Thread t   new Thread new MyThread                 t setName  MyThread   i               t start                      int threadCount   0          Set lt Thread gt  threadSet   Thread getAllStackTraces   keySet            for   Thread t   threadSet               if   t getThreadGroup      Thread currentThread   getThreadGroup                     System out println  Thread    t      state   t getState                       threadCount                                  System out println  Thread count started by Main thread   threadCount            class MyThread implements Runnable      public void run            try              Thread sleep 2000            catch Exception err               err printStackTrace                        Output   java ThreadStatus  Thread  Thread MyThread 0 5 main  state TIMED WAITING Thread  Thread main 5 main  state RUNNABLE Thread  Thread MyThread 1 5 main  state TIMED WAITING Thread  Thread MyThread 4 5 main  state TIMED WAITING Thread  Thread MyThread 2 5 main  state TIMED WAITING Thread  Thread MyThread 3 5 main  state TIMED WAITING Thread count started by Main thread 6   If you remove below condition  if   t getThreadGroup      Thread currentThread   getThreadGroup      You will get below threads in output too  which have been started by system   Reference Handler  Signal Dispatcher Attach Listener and Finalizer

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ManagementFactory getThreadMXBean   getThreadCount   doesn t limit itself to thread groups as Thread activeCount   does

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Get number of threads using jstack jstack  lt PID gt    grep  java lang Thread State    wc -l  The result of the above code is quite different from top -H -p  lt PID gt  or ps -o nlwp  lt PID gt  because jstack gets only threads from created by the application  In other words  jstack will not get GC threads

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Using Linux Top command  top -H -p  process id   you could get process id of one program by this method    ps aux   grep  your program name   for example     ps aux   grep user py

[java] How to get the number of threads in a Java process

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