I am cross posting this from the nio-dev mailing list. The javadoc for SoftReference states:
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError. As pointed out in the nio-dev thread, there are some exceptions to this when it is obvious that clearing soft references would not prevent the OOME. A simple example is trying to instantiate an array of size Integer.MAX_VALUE. My question, however, relates to allocating direct ByteBuffer instances. Would it be possible to clear softly-reachable direct ByteBuffer instances prior to throwing java.lang.OutOfMemoryError: Direct buffer memory? This would make it much simpler (and safer) to implement a cache of direct ByteBuffer instances for re-use. A potential use for this would be in sun.nio.ch.Util. JDK-8175230 introduced the ability to control the max size of direct ByteBuffer to cache, so as to avoid the OOME. There could be value in moving to a tiered caching strategy. The current approach of thread local values could be used for small instances. A second tier, for larger sizes (say >=64KB) could be shared among all threads and the cached instances be softly referenced. This would continue to avoid an OOME, but provide reuse for large direct ByteBuffers, which can be expensive to allocate/destroy. Thanks, Brett
