ClassLoader Leak Keepalive Timer is a feature in Java Virtual Machine that helps to prevent classloader leaks. In this article, we will explain what classloader leak is, how it occurs, and how the keepalive timer feature can help you avoid it.
What is ClassLoader Leak?
Classloader is a fundamental part of the Java Runtime Environment (JRE) that loads classes into the memory when they are first accessed by an application. When the class is no longer needed, the classloader is expected to release the memory occupied by the class.
However, in some cases, the classloader may hold on to the class object, preventing the garbage collector from reclaiming the memory. This is known as classloader leak.
What Causes ClassLoader Leak?
ClassLoader leaks can occur due to various reasons. One of the most common causes is when an application creates a new classloader each time it loads a new class. If the classloader is not explicitly released after the class is unloaded, it can lead to a memory leak.
Another reason for classloader leaks is when a classloader is created in a static context. Since static objects are not garbage collected until the application exits, the classloader and the classes it loads will remain in memory even if they are no longer needed.
How Does ClassLoader Leak Affect Performance?
ClassLoader leaks can have a significant impact on the performance of your application. When a classloader holds on to a class object, it prevents the garbage collector from reclaiming the memory. This can lead to increased memory usage and, ultimately, cause the application to run out of memory.
ClassLoader leaks can also increase the startup time of your application since the JVM has to load all the unnecessary classes into memory. This can result in longer application startup times, which can be frustrating for users.
What is ClassLoader Leak Keepalive Timer?
ClassLoader Leak Keepalive Timer is a feature in Java Virtual Machine that helps to prevent classloader leaks. It works by periodically checking the classloader to see if it is still needed. If the classloader is no longer being used, it releases the memory occupied by the classloader and the classes it loaded.
The keepalive timer feature is enabled by default in Java 8 and above. However, if you are using an older version of Java, you may need to enable it manually.
How Does ClassLoader Leak Keepalive Timer Work?
The keepalive timer feature works by periodically checking the classloader to see if it is still being used. If the classloader is no longer needed, it releases the memory occupied by the classloader and the classes it loaded.
The keepalive timer runs on a separate thread and is configurable using the JVM option "sun.misc.URLClassPath.disableJarChecking". By default, the timer runs every 12 hours, but you can adjust the frequency by setting the "sun.misc.URLClassPath.jarTimeout" property.
How to Enable ClassLoader Leak Keepalive Timer?
If you are using Java 8 or above, the keepalive timer feature is enabled by default. However, if you are using an older version of Java, you may need to enable it manually.
To enable the keepalive timer feature, you need to add the following JVM option to your command-line arguments:
-XX:+UseGCOverheadLimit -XX:+ExplicitGCInvokesConcurrent
Conclusion
ClassLoader leaks can have a significant impact on the performance of your application. However, by using the ClassLoader Leak Keepalive Timer feature, you can prevent classloader leaks and improve the performance of your application.
