Shulou(Shulou.com)06/01 Report--

This article mainly explains "how to use VisualVM to analyze performance", the content of the article is simple and clear, easy to learn and understand, now please follow the editor's ideas slowly in depth, together to study and learn "how to use VisualVM to analyze performance" bar!

Here you need to use a tool that comes with java, VisualVM. Download a VisualVM using IDEA.

1. Check the JVM memory of the program

First of all, do not set the task parameters, and then write a program.

Public class JavaHeapTest {

Public final static int OUTOFMEMORY = 200000000

Private String oom

Private int length

StringBuffer tempOOM = new StringBuffer ()

Public JavaHeapTest (int leng) {

This.length = leng

Int I = 0

While (I < leng) {

ITunes +

Try {

TempOOM.append ("a")

} catch (OutOfMemoryError e) {

E.printStackTrace ()

Break

}

}

This.oom = tempOOM.toString ()

}

Public String getOom () {

Return oom

}

Public int getLength () {

Return length

}

Public static void main (String [] args) {

JavaHeapTest javaHeapTest = new JavaHeapTest (OUTOFMEMORY)

System.out.println (javaHeapTest.getOom () .length ())

}

}

Then use VIsualVM to run the program.

The program runs, but for the first time you need to set the location of the VisualVM

The heap after the program is running.

The figure above is done without setting any program, so why do you need to look at the size of the heap? because instances of objects stored in the heap generally need to set this value. When no settings are made, you will see that the memory of the heap may reach 1G. Sometimes you need to simulate the Java memory size on the online environment and set the heap size for the next year in IDEA. Here, the initialization and maximum values of the heap are the same, so as to avoid JVM redistributing memory after each garbage collection.

Run the program after setting, the heap memory changes to the set size, but there may be an exception at this time, java.lang.OutOfMemoryError: Java heap space appears on my computer, the exception is caused by the setting of too small heap memory, but in general this will not happen, because the above program does not need a particularly large program, may be the reason for my laptop.

The above looks at the size of the heap, and then you can look at what is stored in the heap. When the program is running, you need to quickly click on the heap dump, and then you will see the following

Double-click a list to view the contents of it, and the most stored is the tempOOM parameter set in the program. At this time, you know what is the largest storage in the heap. If it is another program, a certain field takes up a lot of memory, which may be something wrong with the program, so you need to optimize that field.

Second, check the threads of the program

Next, run the following program:

Public class DeadLock {

Public static void main (String [] args) {

Resource R1 = new Resource ()

Resource R0 = new Resource ()

Thread myTh2 = new LockThread1 (R1, R0)

Thread myTh0 = new LockThread0 (R1, R0)

MyTh2.setName ("DeadLock-1")

MyTh0.setName ("DeadLock-0")

MyTh2.start ()

MyTh0.start ()

}

}

Class Resource {

Private int i

Public int getI () {

Return i

}

Public void setI (int I) {

This.i = I

}

}

Class LockThread1 extends Thread {

Private Resource r1, r2

Public LockThread1 (Resource R1, Resource R2) {

This.r1 = R1

This.r2 = R2

}

@ Override

Public void run () {

Int j = 0

While (true) {

Synchronized (R1) {

System.out.println ("The first thread got R1s lock" + j)

Synchronized (R2) {

System.out.println ("The first thread got R2's lock" + j)

}

}

Jacks +

}

}

}

Class LockThread0 extends Thread {

Private Resource r1, r2

Public LockThread0 (Resource R1, Resource R2) {

This.r1 = R1

This.r2 = R2

}

@ Override

Public void run () {

Int j = 0

While (true) {

Synchronized (R2) {

System.out.println ("The second thread got R2's lock" + j)

Synchronized (R1) {

System.out.println ("The second thread got R1s lock" + j)

}

}

Jacks +

}

}

}

After the program runs, check the thread label and directly alarm the thread that has a deadlock.

The above program can see that the blue part is the thread running normally, and the yellow part is waiting.

Third, use VisualGC to check the heap memory GC of the younger generation and the old generation. If there is frequent GC, then it may be that there is insufficient memory, so you need to increase the heap memory.

Most of the GC in the above figure is in the Eden area, that is, the objects are born and died, and the GC time collects 0 GC, so the program can run all the time (here the program runs for a short time, and you can get more information after a long time observation. If the heap memory is set very small, then GC often occurs.)

Thank you for your reading, the above is the content of "how to use VisualVM to analyze performance". After the study of this article, I believe you have a deeper understanding of how to use VisualVM to analyze performance, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.