SlabItem* SlabAllocator::allocateItemFromSlab(SlabRow* slr)
{
if (slr == nullptr) {
return nullptr;
}
SlabItem* item = nullptr;
SlabHeader* sh = slr->firstSlab; // first slab guaranteed pre-allocated
// search all headers until you can satisfy the request
SlabHeader* shPrev = sh;
sh = sh->next;
while (sh != nullptr) {
if (sh->itemsRemaining > 0) {
break;
}
shPrev = sh;
sh = sh->next;
}
if (sh == nullptr) {
sh = shPrev->next = createSlab(itemSize);
}
// if request still fails, we return nullptr
if (sh != nullptr) {
item = sh->nextFreeItem;
sh->nextFreeItem = sh->nextFreeItem->next;
--(sh->itemsRemaining);
}
return item;
}
void* ArenaImpl<kChunkBytes>::allocSlow(size_t nbytes) {
// Large allocations go directly to malloc without discarding our
// current chunk.
if (UNLIKELY(nbytes >= kChunkBytes)) {
#if defined(VALGRIND) || !defined(USE_JEMALLOC)
// We want all our pointers to be kMinBytes - 1 byte aligned.
// Without jemalloc we have to do that by hand.
auto extra = kMinBytes - 1;
#else
auto extra = 0;
#endif
char* ptr = static_cast<char*>(malloc(nbytes + extra));
#ifdef DEBUG
m_externalAllocSize += nbytes + extra;
#endif
m_externalPtrs.push(ptr); // save ptr before aligning it
// align up to (extra + 1) bytes
ptr = (char*)((uintptr_t(ptr) + extra) & ~extra);
assert((intptr_t(ptr) & (kMinBytes - 1)) == 0);
return ptr;
}
createSlab();
return alloc(nbytes);
}
SlabRow* SlabAllocator::createSlabRow(unsigned int itemsize)
{
if ((mUnmappedHeap + SlabAllocator::slabRowAndSlabSize) > (mHeap + mHeapSize)) {
return nullptr;
}
SlabRow* slr = mUnmappedHeap;
mUnmappedHeap += sizeof(SlabRow);
slr->itemSize = itemSize;
slr->firstSlab = createSlab(itemSize);
slr->next = nullptr;
return slr;
}
