Will system.gc() force garbage collection?

Found this in another thread.

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In the Java source code you can find the following comment:

// We don't want shrink all the way back to initSize if people call

// System.gc(), because some programs do that between "phases" and then

// we'd just have to grow the heap up again for the next phase. So we

// damp the shrinking: 0% on the first call, 10% on the second call, 40%

// on the third call, and 100% by the fourth call. But if we recompute

// size without shrinking, it goes back to 0%.

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caplm_71a at 2007-7-14 23:43:50 >

If you use Sun's HotSpot 1.5.0 JVM (or later) with the -XX:+UseConcurrentMarkSweepGC (low-latency) garbage collector, you can use the additional flag -XX:+ExplicitGCInvokesConcurrent to have calls to System.gc() initiate a concurrent collection, rather than cause a stop-the-world compacting collection, which calling System.gc() usually does. Most people who run the low-latency collector are trying to avoid the pauses caused by compacting collections.

If you have some annoying third-party library that calls System.gc() and that upsets your application's performance, you can use the additional flag -XX:+DisableExplicitGC to make calls to System.gc() into no-ops. That works with whatever collector you are using.

Peter.Kessler@Sun.COMa at 2007-7-14 23:43:50 >