Java heap memory

Question

I have a question regarding the Java heap space.

I have a program that uses geotools to create a graph from a street network. I do some stuff with that but I run into a OutOfMemoryError but I am unsure why. I use the following code to get the amount of free memory.

Runtime rt = Runtime.getRuntime();
long maxMb = rt.freeMemory()/(1024*1024);
System.out.println("Your JVM has " + maxMb + " MB of memory left");

And when I run my program, there seems to be enough memory (see output). This console output is done right before the OutOfMemory Error occurs. So what is going wrong? When I enlarge the Java heap space, the OutOfMemory Error occurs nevertheless (but with 1461 MB left). I have no idea why that happens? Any ideas?

Your JVM has 981 MB of memory left
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source)
at java.util.Arrays.copyOf(Unknown Source)
at java.util.ArrayList.grow(Unknown Source)
at java.util.ArrayList.ensureCapacityInternal(Unknown Source)
at java.util.ArrayList.add(Unknown Source)
at masterthesis.datastructures.Stroke.addStrokeSegment(Stroke.java:78)
at masterthesis.algorithms.StrokeBuilder.buildStroke(StrokeBuilder.java:145)
at org.geotools.test.Main.main(Main.java:109)

May there is some memory leak (or) the image you are loading is larger than avaiable heap? — kosa
– kosa, Commented Nov 1, 2012 at 15:51
It is quite a big program. But the main part is that it has a street network from a shapefile containing 800 streets (line strings). What I do is to create a graph with the graph builder from geotools and then iterate over all the nodes and build so called strokes (= sets of linestrings that have a small deflection angle). During that, the error occurs. — user1765902
– user1765902, Commented Nov 1, 2012 at 16:05

sgp15 · Accepted Answer · 2012-11-01 16:00:19Z

1

Following is one way to debug an OOM.

Adjust your max heap size to a reasonable size e.g. 256 MB. Keeping it reasonably low will help you in step 3.
Add -XX:+HeapDumpOnOutOfMemoryError to command line. This will dump the memory after OOM is encountered.
Open the dump in Eclipse Memory Analyzer and try to analyze biggest objects. It can generate reports that look this.

enter image description here

answered Nov 1, 2012 at 16:00

sgp15

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K Erlandsson · Accepted Answer · 2012-11-01 15:56:25Z

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Since the output indicates that you have a lot of memory left and the error ocurrs during an array list growth my guess is that you have a really huge arraylist that you put objects in. When the JVM tries to grow the list you do not have enough heap space to accomodate the doubling in size of the list.

I would investigate how many objects you actually put in your list with addStrokeSegment().

answered Nov 1, 2012 at 15:56

K Erlandsson

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2 Comments

user1765902 Over a year ago

I think that is it. When I check the size before insertion it is huge even though it shouldn't be. I will try to figure out the error, but If I am unable, I will come back ;)

user1765902 Over a year ago

Found the error. It was a really nasty infinite for-loop that kept invoking the addStrokeSegment() method to generate a huge arraylist. Thanks again! Problem solved

Florent Guillaume · Accepted Answer · 2012-11-01 15:52:18Z

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You should use jmap to get an idea of what your memory is filled with.

answered Nov 1, 2012 at 15:52

Florent Guillaume

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Community · Accepted Answer · 2020-06-20 09:12:55Z

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Try reading Java: OutOfMemoryError Exception and freeMemory()

Runtime.freeMemory() javadoc says that is returns "an approximation to the total amount of memory currently available for future allocated objects"

The way all dynamic structures work is that they allocate memory in chunks. When HashMap is getting full it doesn't allocate extra space for just one more object. It allocates a chunk of some size. I do not know the exact way it works in JVM, but it may try to allocate as much as twice the amount of current memory it uses.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 1, 2012 at 15:52

JavaChipMocha

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