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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
*
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#ifndef yarr_BumpPointerAllocator_h
#define yarr_BumpPointerAllocator_h
#include "PageAllocation.h"
namespace WTF {
#if defined(STARBOARD)
#define MINIMUM_BUMP_POOL_SIZE SB_MEMORY_PAGE_SIZE
#elif WTF_CPU_SPARC
#define MINIMUM_BUMP_POOL_SIZE 0x2000
#elif WTF_CPU_IA64
#define MINIMUM_BUMP_POOL_SIZE 0x4000
#else
#define MINIMUM_BUMP_POOL_SIZE 0x1000
#endif
class BumpPointerPool {
public:
// ensureCapacity will check whether the current pool has capacity to
// allocate 'size' bytes of memory If it does not, it will attempt to
// allocate a new pool (which will be added to this one in a chain).
//
// If allocation fails (out of memory) this method will return null.
// If the return value is non-null, then callers should update any
// references they have to this current (possibly full) BumpPointerPool
// to instead point to the newly returned BumpPointerPool.
BumpPointerPool* ensureCapacity(size_t size)
{
void* allocationEnd = static_cast<char*>(m_current) + size;
ASSERT(allocationEnd > m_current); // check for overflow
if (allocationEnd <= static_cast<void*>(this))
return this;
return ensureCapacityCrossPool(this, size);
}
// alloc should only be called after calling ensureCapacity; as such
// alloc will never fail.
void* alloc(size_t size)
{
void* current = m_current;
void* allocationEnd = static_cast<char*>(current) + size;
ASSERT(allocationEnd > current); // check for overflow
ASSERT(allocationEnd <= static_cast<void*>(this));
m_current = allocationEnd;
return current;
}
// The dealloc method releases memory allocated using alloc. Memory
// must be released in a LIFO fashion, e.g. if the client calls alloc
// four times, returning pointer A, B, C, D, then the only valid order
// in which these may be deallocaed is D, C, B, A.
//
// The client may optionally skip some deallocations. In the example
// above, it would be valid to only explicitly dealloc C, A (D being
// dealloced along with C, B along with A).
//
// If pointer was not allocated from this pool (or pools) then dealloc
// will CRASH(). Callers should update any references they have to
// this current BumpPointerPool to instead point to the returned
// BumpPointerPool.
BumpPointerPool* dealloc(void* position)
{
if ((position >= m_start) && (position <= static_cast<void*>(this))) {
ASSERT(position <= m_current);
m_current = position;
return this;
}
return deallocCrossPool(this, position);
}
size_t sizeOfNonHeapData() const
{
ASSERT(!m_previous);
size_t n = 0;
const BumpPointerPool *curr = this;
while (curr) {
n += m_allocation.size();
curr = curr->m_next;
}
return n;
}
private:
// Placement operator new, returns the last 'size' bytes of allocation for use as this.
void* operator new(size_t size, const PageAllocation& allocation)
{
ASSERT(size < allocation.size());
return reinterpret_cast<char*>(reinterpret_cast<intptr_t>(allocation.base()) + allocation.size()) - size;
}
BumpPointerPool(const PageAllocation& allocation)
: m_current(allocation.base())
, m_start(allocation.base())
, m_next(0)
, m_previous(0)
, m_allocation(allocation)
{
}
static BumpPointerPool* create(size_t minimumCapacity = 0)
{
// Add size of BumpPointerPool object, check for overflow.
minimumCapacity += sizeof(BumpPointerPool);
if (minimumCapacity < sizeof(BumpPointerPool))
return 0;
size_t poolSize = MINIMUM_BUMP_POOL_SIZE;
while (poolSize < minimumCapacity) {
poolSize <<= 1;
// The following if check relies on MINIMUM_BUMP_POOL_SIZE being a power of 2!
ASSERT(!(MINIMUM_BUMP_POOL_SIZE & (MINIMUM_BUMP_POOL_SIZE - 1)));
if (!poolSize)
return 0;
}
PageAllocation allocation = PageAllocation::allocate(poolSize);
if (!!allocation)
return new(allocation) BumpPointerPool(allocation);
return 0;
}
void shrink()
{
ASSERT(!m_previous);
m_current = m_start;
while (m_next) {
BumpPointerPool* nextNext = m_next->m_next;
m_next->destroy();
m_next = nextNext;
}
}
void destroy()
{
m_allocation.deallocate();
}
static BumpPointerPool* ensureCapacityCrossPool(BumpPointerPool* previousPool, size_t size)
{
// The pool passed should not have capacity, so we'll start with the next one.
ASSERT(previousPool);
ASSERT((static_cast<char*>(previousPool->m_current) + size) > previousPool->m_current); // check for overflow
ASSERT((static_cast<char*>(previousPool->m_current) + size) > static_cast<void*>(previousPool));
BumpPointerPool* pool = previousPool->m_next;
while (true) {
if (!pool) {
// We've run to the end; allocate a new pool.
pool = BumpPointerPool::create(size);
previousPool->m_next = pool;
pool->m_previous = previousPool;
return pool;
}
//
void* current = pool->m_current;
void* allocationEnd = static_cast<char*>(current) + size;
ASSERT(allocationEnd > current); // check for overflow
if (allocationEnd <= static_cast<void*>(pool))
return pool;
}
}
static BumpPointerPool* deallocCrossPool(BumpPointerPool* pool, void* position)
{
// Should only be called if position is not in the current pool.
ASSERT((position < pool->m_start) || (position > static_cast<void*>(pool)));
while (true) {
// Unwind the current pool to the start, move back in the chain to the previous pool.
pool->m_current = pool->m_start;
pool = pool->m_previous;
// position was nowhere in the chain!
if (!pool)
CRASH();
if ((position >= pool->m_start) && (position <= static_cast<void*>(pool))) {
ASSERT(position <= pool->m_current);
pool->m_current = position;
return pool;
}
}
}
void* m_current;
void* m_start;
BumpPointerPool* m_next;
BumpPointerPool* m_previous;
PageAllocation m_allocation;
friend class BumpPointerAllocator;
};
// A BumpPointerAllocator manages a set of BumpPointerPool objects, which
// can be used for LIFO (stack like) allocation.
//
// To begin allocating using this class call startAllocator(). The result
// of this method will be null if the initial pool allocation fails, or a
// pointer to a BumpPointerPool object that can be used to perform
// allocations. Whilst running no memory will be released until
// stopAllocator() is called. At this point all allocations made through
// this allocator will be reaped, and underlying memory may be freed.
//
// (In practice we will still hold on to the initial pool to allow allocation
// to be quickly restared, but aditional pools will be freed).
//
// This allocator is non-renetrant, it is encumbant on the clients to ensure
// startAllocator() is not called again until stopAllocator() has been called.
class BumpPointerAllocator {
public:
BumpPointerAllocator()
: m_head(0)
{
}
~BumpPointerAllocator()
{
if (m_head)
m_head->destroy();
}
BumpPointerPool* startAllocator()
{
if (!m_head)
m_head = BumpPointerPool::create();
return m_head;
}
void stopAllocator()
{
if (m_head)
m_head->shrink();
}
size_t sizeOfNonHeapData() const
{
return m_head ? m_head->sizeOfNonHeapData() : 0;
}
private:
BumpPointerPool* m_head;
};
}
using WTF::BumpPointerAllocator;
#endif /* yarr_BumpPointerAllocator_h */