Java garbage collector - When does it collect? -

What determines when the garbage collector actually collects? Does it happen after a certain time or in a certain amount of memory is used? Or are there other factors?

It runs when it determines that it's time to run. A common strategy in generational garbage collectors is to run the collector when allocation of generation-memory fails. That is, every time you allocate a small block of memory (large blocks are usually placed directly into "old" generation), then the system checks whether there is enough space in the General-8 stack, and if not So, it gets run to evacuate the place for allocation to succeed GC. The old data is then moved to the General-1 stack, and when the space is over there, GC runs a collection on it, enhances the data, which is the longest for General-2 stack, and Similarly So GC does not just "run" it can only run on the GN-0 heap (and most of the collection will do the same), or it can actually check each generation to free up a lot of memory (which only Very rarely required).

But it is far from the only strategy, a concurrent GC walks in the background, cleaning up until the program is running. Some GCs can run as part of every memory allocation, an incremental collector can do this, scanning some objects on each memory allocation.

The entire point in the garbage collector is that the user should talk to him without the need for any input. So in general, you can not, and can not predict when it will run.

I believe Sanz JVM did not get a generation GC, long time ago (v1.6 maybe? You have not coded java for ages, so be sure to Not in the form, but I remember that long ago, when one of the sales points for the new version was "a generation GC." At least one day since .NET. 1)

Other JVMs are absolutely free to take whatever kind of strategy they are.

Edit: Java and Generation GC is not correct For more details see below:

1.0 and 1.1 virtual machines use a mark-sweep collector , Which can slice the heap after a garbage collection. Beginning with Java 1.2, virtual machines turned into a generation collector, in which there is a better defragmentation behavior (see).

So Java is actually a generation GC for ages. What's New in Java 6 Garbage - First Garbage Collector (G1) available in Java 6u14. According to: It is not enabled by default parallel collector is still the default GC and is the most effective GC for normal home use. G1 means having an option for concurrent collector. It is more predictable and is designed to enable faster allocation with the memory areas design.