Hello all, So to those of you familiar with the freelists you know that it works this way the head pointer uses the upper 16 bits for a version to prevent the ABA problem. The big drawback to this is that it requires the following NASTY macros to get at the pointer or the version:
#define FREELIST_POINTER(_x) ((void*)(((((intptr_t)(_x).data)<<16)>>16) | \ (((~((((intptr_t)(_x).data)<<16>>63)-1))>>48)<<48))) // sign extend #define FREELIST_VERSION(_x) (((intptr_t)(_x).data)>>48) #define SET_FREELIST_POINTER_VERSION(_x,_p,_v) \ (_x).data = ((((intptr_t)(_p))&0x0000FFFFFFFFFFFFULL) | (((_v)&0xFFFFULL) << 48)) Additionally, since this only leaves 16 bits it limits the number of versions you can have. Well more and more x86_64 processors support DCAS (double word compare and swap / 128bit CAS). This means that we can use 64bits for a version which basically makes the versions unlimited but more importantly it takes those macros above and simplifies them to: #define FREELIST_POINTER(_x) (_x).s.pointer #define FREELIST_VERSION(_x) (_x).s.version #define SET_FREELIST_POINTER_VERSION(_x,_p,_v) \ (_x).s.pointer = _p; (_x).s.version = _v As you can imagine this will have a performance improvement, in my simple tests I measured a performance improvement of around 6%. As of now I haven't tried doing this with reclaimable freelists, but if this proves fruitful maybe I can work with the taobao guys to make sure it wont have problems with their stuff. This freelist stuff can be very tricky, so I'll ask anyone who is interested or understands this code to please review these changes and most importantly performance test it to make sure this makes. Patch is uploaded to the ticket: https://issues.apache.org/jira/browse/TS-1742 Thanks Brian
