One important advantage of java is programer don't care memory management and
GC handle it well. Maybe this is one reason why java is more popular.
As Java programer you real dont care it? After you meet Out of memory you
will realize it it’s not true.
Java GC and memory is big topic you can get some information in here
Today just let me show how to identify memory leak quickly.
Let quickly review demo java code, it’s one kind of memory leak in our code,
using static collection and always add some object.
import java.util.ArrayList;import java.util.List;
public class MemoryTest { public static void main(String[] args)
{ new Thread(new MemoryLeak(), "MemoryLeak").start();
}}
class MemoryLeak implements Runnable { public static
List<Integer> leakList = new ArrayList<Integer>(); public
void run() { int num =0; while(true) { try
{ Thread.sleep(1); } catch (InterruptedException
e) { } num++; Integer i = new
Integer(num); leakList.add(i);
} }}
run it with java -verbose:gc -XX:+PrintGCDetails -Xmx60m
-XX:MaxPermSize=160m MemoryTest
after about some minuts you will get
Exception in thread "MemoryLeak" java.lang.OutOfMemoryError: Java heap
space at java.util.Arrays.copyOf(Arrays.java:2760) at
java.util.Arrays.copyOf(Arrays.java:2734) at
java.util.ArrayList.ensureCapacity(ArrayList.java:167) at
java.util.ArrayList.add(ArrayList.java:351) at
MemoryLeak.run(MemoryTest.java:25) at
java.lang.Thread.run(Thread.java:619)Heap def new generation total
18432K, used 3703K [0x045e0000, 0x059e0000, 0x059e0000) eden space 16384K,
22% used [0x045e0000, 0x0497dde0, 0x055e0000) from space 2048K, 0% used
[0x055e0000, 0x055e0000, 0x057e0000) to space 2048K, 0% used
[0x057e0000, 0x057e0000, 0x059e0000) tenured generation total 40960K, used
40959K [0x059e0000, 0x081e0000, 0x081e0000) the space 40960K, 99% used
[0x059e0000, 0x081dfff8, 0x081e0000, 0x081e0000) compacting perm gen total
12288K, used 2083K [0x081e0000, 0x08de0000, 0x10de0000) the space 12288K,
16% used [0x081e0000, 0x083e8c50, 0x083e8e00, 0x08de0000)No shared spaces
configured.
OK let us quickly identify it using JProfile
Download JProfile in here
Run JProfile and attach MemoryTest get largest size of Objects in Memory View in here is Integer
then select Integer and go to Heap Walker.
get GC Graph for this object
Then you get detail code raise this issue quickly now.
That is enjoy it.
