JVM memory leak investigation (visual vm)
Memory leak: The end of the object usage, the memory space occupied by the object is not recycled during garbage collection
Cause: The object is referenced by long-lived variables, such as static variables
Consequences: If a large number of objects are used but cannot be recycled, it may cause a memory overflow (cannot allocate memory for new objects)
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Examples
class MyObject{
private int _1m=1024*1024;
private byte[] b;
public MyObject(){
this.b=new byte[_1m];
}
}
public class Test11 {
private static List<MyObject> list=new ArrayList<>();
public static void main(String[] args) throws Exception {
for (int i=0;i<1000;i++){
list.add(new MyObject());
System.out.println("add "+i);
try{
Thread.sleep(1000);
}catch (Exception e){
e.printStackTrace();
}
}
System.out.println(list);
}
}
Note: The objects created in the loop body are added to the list. The list is a global variable, and the object will not be released after the method line ends, causing memory leak
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Console output
Virtual machine parameters: -Xms500m -Xmx500m
。。。
add 240
add 241
add 242
add 243
add 244
add 245
add 246
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at runtime.MyObject.<init>(Test11.java:12)
at runtime.Test11.main(Test11.java:22)
Description: The object myObject created in the loop cannot be released, causing memory overflow
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Visual vm memory leak investigation
visual gc tags
During the operation before and after, the space used by the old generation gradually increased, and eventually the memory overflowed, judging that it may cause a memory leak
sampler: heap dump, execute heap dump again after a while
Comparison of two heap dumps before and after
Comparison found that MyObject objects increased significantly
myObject ==》 open in new tab
myObject references
Memory leak objects are in the arrayList linked list
