RFR (M) 8055283: Expand ResourceHashtable with C_HEAP allocation, removal and some unit tests (original) (raw)

Mikael Gerdin mikael.gerdin at oracle.com
Fri Oct 16 08:30:08 UTC 2015

Hi all,

Here's an old favorite. I'm yet again in need of a simple-to-use hash table in a place where resource allocation is impossible to use.

The idea is to add a ResourceObj::allocation_type template parameter to ResourceHashtable to allow a user to specify C-heap allocation using ResourceObj::C_Heap.

Currently if one tries to do { ResourceMark rm; ResourceHash* hash = new (ResourceObj::C_HEAP) ResourceHash(); hash->put(...) } hash->get(...)

The get()-call will crash because the allocation of the hash table nodes does not respect the C_HEAP parameter.

To sweeten the deal a little I add support for removing elements and also a small bunch of unit tests to verify that the operations work as expected.

I also discovered a small issue with the primitive_hash() function which is the default one: 36 template unsigned primitive_hash(const K& k) { 37 unsigned hash = (unsigned)((uintptr_t)k); 38 return hash ^ (hash > 3); // just in case we're dealing with aligned ptrs 39 }

It xors hash with the boolean expression (hash > 3) instead of what was probably intended (hash >> 3) to deal with aligned pointers as the comment suggests. It appears that the only user of ResourceHash which doesn't specify its own hash function is MethodFamily::_member_index so it would be nice if someone could point me at any default method tests to verify that a proper hash function doesn't break anything.

Bug: https://bugs.openjdk.java.net/browse/JDK-8055283 Webrev: http://cr.openjdk.java.net/~mgerdin/8055283/webrev.1/

Testing: JPRT RBT (Kitchensnk, hotspot/test/:hotspot_all)

Thanks! /Mikael

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