CODEWITHSUNDEEP
javamemorymemory-leaksjvm
Johnydep
Johnydep

Reputation: 6277

Check available heapSize programmatically?

I am using Eclipse. The problem is my application crashes if the allocated memory is less then 512MB. Now is there anyway to check the available memory for a program before starting heavy memory exhaustive processing? For example, I know we can check available JVM heap size as:

long heapSize = Runtime.getRuntime().totalMemory();
System.out.println("Heap Size = " + heapSize);

Problem is, this gives the JVM heap size. Even increasing it does not work using Eclipse. In Eclipse, if I change the VM arguments then it works. However the printout from above statements is always the same. Is there any command through which I can exactly know how much memory I am allocated for a particular application?

Upvotes: 13

Views: 23224

Answers (3)

Ingo
Ingo

Reputation: 635

maybe an useful update using Java 17 to 19: After several trials with getRuntime() and old/Eden/Survivor Space I came back to use getRuntime() which seem to be 'faithful' now:

With Java 17-19 therefore I propose to use the heap size functions of getRuntime():

Runtime env = Runtime.getRuntime();

System.out.println("Max Heap Size = maxMemory() = " + env.maxMemory()); //max heap size from -Xmx, i.e. is constant during runtime
System.out.println("Current Heap Size = totalMemory() = " +  env.totalMemory()); //currently assigned  heap
System.out.println("Available in Current Heap = freeMemory() = " + env.freeMemory()); //current heap will extend if no more freeMemory to a maximum of maxMemory
System.out.println("Currently Used Heap = " + (env.totalMemory()-env.freeMemory()) );
System.out.println("Unassigned Heap = " + (env.maxMemory()-env.totalMemory()));
System.out.println("Currently Totally Available Heap Space = "+ ((env.maxMemory()-env.totalMemory()) + env.freeMemory()) ); //available=unassigned + free

Upvotes: 4

Rob Oxspring
Rob Oxspring

Reputation: 2935

totalMemory() returns the current total memory used, and not the total available memory. To query the maximum available memory then use maxMemory() (aka java -Xmx option):

long heapSize = Runtime.getRuntime().maxMemory();
System.out.println("Heap Size = " + heapSize);

Upvotes: 2

Mike Lue
Mike Lue

Reputation: 839

You could use JMX to collect the usage of heap memory at runtime.

Code Example:

import java.lang.management.ManagementFactory;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryType;
import java.lang.management.MemoryUsage;

for (MemoryPoolMXBean mpBean: ManagementFactory.getMemoryPoolMXBeans()) {
    if (mpBean.getType() == MemoryType.HEAP) {
        System.out.printf(
            "Name: %s: %s\n",
            mpBean.getName(), mpBean.getUsage()
        );
    }
}

Output Example:

Name: Eden Space: init = 6619136(6464K) used = 3754304(3666K) committed = 6619136(6464K) max = 186253312(181888K)
Name: Survivor Space: init = 786432(768K) used = 0(0K) committed = 786432(768K) max = 23265280(22720K)
Name: Tenured Gen: init = 16449536(16064K) used = 0(0K) committed = 16449536(16064K) max = 465567744(454656K)

If your have question about "Eden Space" or "Survivor Space", check out How is the java memory pool divided

Upvotes: 22

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