B4J Code Snippet Garbage collection

Hello

For those of you interested in GC here is a class I have in a B4J server:

Sub Class_Globals
 
   Private tmrHook           As Timer
   Private gcTime           As Long
   Private freq_gc           As Int = 1
 
End Sub

Public Sub Initialize
 
 
   ' // 3 seconds
   tmrHook.Initialize("tmrHook", 3000)
   tmrHook.Enabled = True
   threadName = getcurrentThreadName
 
   ' // set the initial GC time
   gcTime =DateTime.Now + (DateTime.TicksPerMinute * freq_gc)
   writelog("Background Hello Helper Thread Started, GC Frequency Check Every " &  freq_gc & " Minutes" )
 
   StartMessageLoop '<- don't forget!
 
End Sub

Sub tmrHook_Tick
 
   ' // do GC
   If gcTime < DateTime.Now Then
       process_gc
       ' // set next time
       gcTime =DateTime.Now + (DateTime.TicksPerMinute * freq_gc)
   End If
 
End Sub

Sub process_gc
 
   Dim jo As JavaObject = Me
 
 
   log("Total designated memory " & jo.RunMethod("getTotal",Null))
   log("Before GC, Java heap currently used by instantiated objects " & jo.RunMethod("getUsed",Null))
   log("Before GC, Current allocated free memory " & jo.RunMethod("getAllocatedFree",Null))
   jo.RunMethod("do_garbage_collection",Null)
   log("After GC, Current allocated free memory " & jo.RunMethod("getAllocatedFree",Null))
   log("After GC, Java heap currently used by instantiated objects " & jo.RunMethod("getUsed",Null))
 
End Sub

Sub getcurrentThreadName As String
    
    Dim t As JavaObject
    Return t.InitializeStatic("java.lang.Thread").RunMethodJO("currentThread", Null).RunMethod("getName", Null)
    
End Sub

#if java

   import java.util.*;
 
   public void do_garbage_collection()   {        
       Runtime rs = Runtime.getRuntime();
       rs.gc();
     }
    
   public long getAllocatedFree() {
       Runtime rs = Runtime.getRuntime();
        return rs.freeMemory();
    }
 
   public long getAllocatedTotal() {
       Runtime rs = Runtime.getRuntime();
        return rs.totalMemory();
    }
 
   public long getUsed() {
       Runtime rs = Runtime.getRuntime();
        return rs.totalMemory() - rs.freeMemory();
    }
 
   public long getTotal() {
       Runtime rs = Runtime.getRuntime();
        return rs.maxMemory();
    }
 
#End If

Regards

John.

EDIT: Please note that in this example the frequency is set to 1 minute, this is just to allow you see the memory metrics. I don't recommend that you use this frequency in a production environment.

 

[avalle]

threadName = getcurrentThreadName

Hi John, this is quite an old thread, I know, but the topic is interesting to me.
Can you explain the line above?

 

[Jmu5667]

Hi John, this is quite an old thread, I know, but the topic is interesting to me.
Can you explain the line above?

sure, this code gets the current thread name that a process is running in. I find it quite useful so I can monitor thread activity in a b4j server(no-ui) application.

I just noticed the code was not in the original example, that has now been updated

Sub getcurrentThreadName As String
   
    Dim t As JavaObject
    Return t.InitializeStatic("java.lang.Thread").RunMethodJO("currentThread", Null).RunMethod("getName", Null)
   
End Sub

 

[avalle]

Nice thanks!

 

[Jmu5667]

Nice thanks!

Your Welcome, glad to be of help

 

[jmon]

EDIT: Please note that in this example the frequency is set to 1 minute, this is just to allow you see the memory metrics. I don't recommend that you use this frequency in a production environment.

Hi, what would be the recommended frequency in production? Also, Java FX already has some sort of garbage collection I believe, is this function redundant, or does it work differently?

 

[agraham]

Hi, what would be the recommended frequency in production?

Never unless you have a very good reason. The Java Virtual Machine does the garbage collection itself. Nothing to do with Java FX.

 

[Jmu5667]

Hi, what would be the recommended frequency in production? Also, Java FX already has some sort of garbage collection I believe, is this function redundant, or does it work differently?

Hi jmon

I looked into the JAVA VM GC model and it is decides when it will perform it. I use this method on all our B4J servers so I manage when GC is done. If you have a very active server doing a lot client connections and SQL server requests you really want your server app to be at it best performance. I usually do a GC every 15 minutes. I spent a lot of time analysing threading and the memory usage(https://visualvm.github.io/) and understanding how and why it does what it does.

You can do some tests yourself. It's not for everyone, but it serves our company's needs. I hope it it of some value to you.

Regards

John.