franz1981 edited a comment on issue #2832: ARTEMIS-2482 Large messages could leak native ByteBuffers URL: https://github.com/apache/activemq-artemis/pull/2832#issuecomment-530284944 @wy96f Yes and no :) They would leak (at first look, but let me take a better look), but they just contain wrappers to direct memory that cannot be released (is part of the pool and they have no cleaner). The impact should be way less then `IOUtil` that pool native `ByteBuffer`s holding exclusively native memory that won't be reused anymore... Ideally we shouldn't have *any* thread locals, but we use them for several stuff (including the NIO factories and page read/write): I'm planning to replaced them by using the Netty pool, because of the difference on how thread locals are used. Our thread locals in Artemis just hold memory that cannot be reused if not by the same thread, while for Netty, thread locals are just a way to cache wrappers that has a very limited impact on GC, while the pool really allows to reuse memory where is most needed... Just to add more detail: consider that `PooledBytebufAllocator.PoolThreadLocalCache::initialValue` contains this comment, while creating a thread-local `PoolThreadCache`: ``` @Override protected synchronized PoolThreadCache initialValue() { final PoolArena<byte[]> heapArena = leastUsedArena(heapArenas); final PoolArena<ByteBuffer> directArena = leastUsedArena(directArenas); Thread current = Thread.currentThread(); if (useCacheForAllThreads || current instanceof FastThreadLocalThread) { return new PoolThreadCache( heapArena, directArena, tinyCacheSize, smallCacheSize, normalCacheSize, DEFAULT_MAX_CACHED_BUFFER_CAPACITY, DEFAULT_CACHE_TRIM_INTERVAL); } // No caching so just use 0 as sizes. return new PoolThreadCache(heapArena, directArena, 0, 0, 0, 0, 0); } ``` So, if we are not very happy about the Netty caching on non-Netty threads, we can disable those caches by setting `-Dio.netty.allocator.useCacheForAllThreads=false`
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