Reputation: 50563

How can I disable Java garbage collector?

We have a PHP webapp that calls a Java binary to produce a PDF report (with JasperReports). The Java binary outputs the PDF to standard output and exits; the PHP then sends the PDF to browser. This Java command lasts about 3 to 6 seconds, and I think when it lasts 6 second it's because the GC kicks in. I would like to disable the GC because anyway when the command exits all memory is returned.

I would like to know how to disable it for Java 1.4.2 and for Java 1.6.0 because we are currently testing both JVM to see which performs faster..

Upvotes: 42

Answers (10)

barneypitt

Reputation: 1162

Contrary to what everyone else has said, there is a way to suspend GC, though it's very convoluted.

If you call a native function via JNI, in between the native code calling GetPrimitiveArrayCritical and ReleasePrimitiveArrayCritical, GC is suspended. It has to do this because it is the mechanism used for sharing memory between Java and native code, and GC may move objects around in memory.

So to utilise this you'd need to create a JNI function which calls the former, then polls a flag written to that critical array (which could just be a byte[1]) waiting till it sees the flag before calling the latter. When the Java code wishes to suspend GC it would call the JNI method and when it wishes to resume GC, set the aforementioned flag (I believe reads/writes to the critical array are volatile, so the native code would see the flag immediately).

Now I'm not saying this is a good idea, and certainly not the correct solution to the OP's problem. But if you absolutely had to temporarily suspend GC for some reason (perhaps you wish to manipulate raw memory via sun.misc.Unsafe and needed to ensure objects were not moved about by GC whilst doing so), that's how you could achieve it.

Upvotes: 0

Cameron McKenzie

Reputation: 3880

Java 11 gives you the binary option to either have Java GC on, or have Java GC turned off. To turn off Java GC you use the Epsilon Garbage Collector which must be turned off on the command line. On Java 11, use the following two JVM arguments:

-XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC

Without the UnlockExperimentalVMOptions argument, the JVM will fail to start, so make sure it's included.

Can't Stop Java GC

Unfortunately, if you're not using Epsilon GC, there is no way to disable, stop or prevent garbage collection from happening. Just like not being able to trigger GC, you can't stop Java GC either. The algorithms are non-deterministic. Only the JVM can control when they occur.

Upvotes: 9

aventurin

Reputation: 2203

Java 11 comes with an no-op garbage collector.

It can be enabled by the -XX:+UseEpsilonGC option at JVM start.

According to the JEP decription one of its goals is to make certain short-lived jobs more efficient, what might be you use case:

Extremely short lived jobs. A short-lived job might rely on exiting quickly to free the resources (e.g. heap memory). In this case, accepting the GC cycle to futilely clean up the heap is a waste of time, because the heap would be freed on exit anyway. Note that the GC cycle might take a while, because it would depend on the amount of live data in the heap, which can be a lot.

Upvotes: 23

Rodrigo Hernandez

Reputation: 91

To avoid garbage collector release a variable or property from any object, you must set this property (released by gc) as static in your class it was my solution.

Example:

private static String myProperty;

Upvotes: -5

Ceilingfish

Reputation: 5455

There is no way to disable garbage collection entirely. Garbage collection is only run when the JVM runs out of space, so you could give the program more memory. Add these command line options to the Java command

-Xmx256M -Xms256M

This gives the program 256Mb of ram (the default is 64Mb). Garbage collection will not take 3 seconds for a default size JVM though, so you might want to investigate more closely what the program is doing. Yourkit profiler is very useful for figuring out what is taking a long time.

Upvotes: 34

display101

Reputation: 2085

As everyone as said you can't disable GC in the JVM, which makes sense right, because if you could there'd be memory leaks due to java not having an explicit way for the developer to delete the heap data.

Do you have access to the source of this java binary? If so it might be worth analysing it and seeing if there's any bottle-necks which could be better written to cut down on GC activity. This could be done with most java profilers, like JProbe for example.

Upvotes: -2

Paul Jowett

Reputation: 6581

It sounds like you are trying to save time, but going about it the wrong way. The time saved in disabling garbage collection would be trivial (for a single task) compared to the time taken to launch and shutdown the java process. You might want to consider having a java process launch that you can ask multiple times to do the work you require if run-time performance is your goal.

Upvotes: 38

Michael Aaron Safyan

Reputation: 95499

You can use the -Xmx option to set the maximum heap size; using a larger heap should prevent the VM from runnning out of memory and, thereby, requiring garbage collection so soon.

Upvotes: 2

Mark

Reputation: 29119

Are you sure that it is garbage collection causing the slowdown? Have you run java with -verbose:gc to see what is happening?

You cannot disable garbage collection on the JVM. You could however look at tuning the garbage collector for better performance.

Upvotes: 1

unbeli

Reputation: 30228

GC only kicks in when JVM is short on memory, so you either GC or die. Try turning on verbose GC and see if it actually takes significant amount of time.

java -verbose:gc

Upvotes: 31

How can I disable Java garbage collector?

Answers (10)

Can't Stop Java GC

Related Questions