SizeClasses() — netty Function Reference

Source Code

buffer/src/main/java/io/netty/buffer/SizeClasses.java lines 117–186

    SizeClasses(int pageSize, int pageShifts, int chunkSize, int directMemoryCacheAlignment) {
        int group = log2(chunkSize) - LOG2_QUANTUM - LOG2_SIZE_CLASS_GROUP + 1;

        //generate size classes
        //[index, log2Group, log2Delta, nDelta, isMultiPageSize, isSubPage, log2DeltaLookup]
        short[][] sizeClasses = new short[group << LOG2_SIZE_CLASS_GROUP][7];

        int normalMaxSize = -1;
        int nSizes = 0;
        int size = 0;

        int log2Group = LOG2_QUANTUM;
        int log2Delta = LOG2_QUANTUM;
        int ndeltaLimit = 1 << LOG2_SIZE_CLASS_GROUP;

        //First small group, nDelta start at 0.
        //first size class is 1 << LOG2_QUANTUM
        for (int nDelta = 0; nDelta < ndeltaLimit; nDelta++, nSizes++) {
            short[] sizeClass = newSizeClass(nSizes, log2Group, log2Delta, nDelta, pageShifts);
            sizeClasses[nSizes] = sizeClass;
            size = sizeOf(sizeClass, directMemoryCacheAlignment);
        }

        log2Group += LOG2_SIZE_CLASS_GROUP;

        //All remaining groups, nDelta start at 1.
        for (; size < chunkSize; log2Group++, log2Delta++) {
            for (int nDelta = 1; nDelta <= ndeltaLimit && size < chunkSize; nDelta++, nSizes++) {
                short[] sizeClass = newSizeClass(nSizes, log2Group, log2Delta, nDelta, pageShifts);
                sizeClasses[nSizes] = sizeClass;
                size = normalMaxSize = sizeOf(sizeClass, directMemoryCacheAlignment);
            }
        }

        //chunkSize must be normalMaxSize
        assert chunkSize == normalMaxSize;

        int smallMaxSizeIdx = 0;
        int lookupMaxSize = 0;
        int nPSizes = 0;
        int nSubpages = 0;
        for (int idx = 0; idx < nSizes; idx++) {
            short[] sz = sizeClasses[idx];
            if (sz[PAGESIZE_IDX] == yes) {
                nPSizes++;
            }
            if (sz[SUBPAGE_IDX] == yes) {
                nSubpages++;
                smallMaxSizeIdx = idx;
            }
            if (sz[LOG2_DELTA_LOOKUP_IDX] != no) {
                lookupMaxSize = sizeOf(sz, directMemoryCacheAlignment);
            }
        }
        this.smallMaxSizeIdx = smallMaxSizeIdx;
        this.lookupMaxSize = lookupMaxSize;
        this.nPSizes = nPSizes;
        this.nSubpages = nSubpages;
        this.nSizes = nSizes;

        this.pageSize = pageSize;
        this.pageShifts = pageShifts;
        this.chunkSize = chunkSize;
        this.directMemoryCacheAlignment = directMemoryCacheAlignment;

        //generate lookup tables
        this.sizeIdx2sizeTab = newIdx2SizeTab(sizeClasses, nSizes, directMemoryCacheAlignment);
        this.pageIdx2sizeTab = newPageIdx2sizeTab(sizeClasses, nSizes, nPSizes, directMemoryCacheAlignment);
        this.size2idxTab = newSize2idxTab(lookupMaxSize, sizeClasses);
    }