应用程序将永远不会执行垃圾收集时有什么条件？

Question

Is there any condition when application will never perform Garbage Collection ? Theoretically is it possible to have such application design ?

Answer 1

Yes, there is. Please read about memory leaks in Java. An example is described in Effective Java Item 6: Eliminate obsolete object references

Answer 2

Garbage collection happens on objects which are not referenced anymore in your application.

With Java 11, there is a way to never purposely perform garbage collection, by running your JVM with the newly introduced Epsilon GC , a garbage collector which handles memory allocation but never releases the allocated memory.

Answer 3

There is at least one product in the market that implements high frequency trading using Java and jvm technology.

Obviously, an application that needs to react in microseconds can't afford a garbage collector to kick in and halt the system for arbitrary periods of time.

In this case, the solution was to write the whole application to never create objects that turn into garbage. For example, all input data is kept in fixed byte arrays (that are allocated once at start time) which are then used as buffers for all kinds of processing.

Unless I am mistaken, you can listen to more details on the software engineering radio podcast. I think it should be this episode: http://www.se-radio.net/2016/04/se-radio-episode-255-monica-beckwith-on-java-garbage-collection/

Answer 4

Is there any condition when application will never perform Garbage Collection ?

You can prevent the GC from running by having a Thread which doesn't reach a safe point.

Unless you use a concurrent collector, the GC will only be performed when a memory region, eg when the Eden or Tenure spaces fill.

If you make these large enough, and your garbage rate low enough, the GC won't run for long enough that you can either perform a GC overnight, in a maintenance window or restart the process.

Theoretically is it possible to have such application design?

I have worked on applications which GC less than once per day (and some of them are restarted every day)

For example, say you produce 300KB of garbage per second, or 1 GB per hour, with a 24 GB Eden size you can run for a whole day without a collection.

In reality, if you move most of your data off-heap eg Chronicle Map or Queue, you might find a 4 GB, can run for a day or even a week with a minor collection.