arena.h

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/* Copyright (c) 2013 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * arena allocator (variable-size blocks, no deallocation).
 */

#ifndef INCLUDED_ALLOCATORS_ARENA
#define INCLUDED_ALLOCATORS_ARENA

#include "lib/allocators/allocator_policies.h"

namespace Allocators {

/**
 * allocator design parameters:
 * - O(1) allocation;
 * - variable-size blocks;
 * - support for deallocating all objects;
 * - consecutive allocations are back-to-back;
 * - no extra alignment nor padding.
 **/
template<class Storage = Storage_Fixed<> >
class Arena
{
    NONCOPYABLE(Arena);
public:
    Arena(size_t maxSize)
        : storage(maxSize)
    {
        DeallocateAll();
    }

    size_t RemainingBytes() const
    {
        return storage.MaxCapacity() - end;
    }

    void* allocate(size_t size)
    {
        return (void*)StorageAppend(storage, end, size);
    }

    void deallocate(void* UNUSED(p), size_t UNUSED(size))
    {
        // ignored
    }

    void DeallocateAll()
    {
        end = 0;
    }

    // @return whether the address lies within the previously allocated range.
    bool Contains(uintptr_t address) const
    {
        return (address - storage.Address()) < end;
    }

private:
    Storage storage;
    size_t end;
};

LIB_API void TestArena();


/**
 * allocator design parameters:
 * - grow dynamically with a fixed chunkSize
 * - for frequent allocations of size << chunkSize
 * - no reallocations, pointers remain valid
 **/
class DynamicArena
{
    struct ArenaChunk
    {
        bool Available(size_t size) const
        {
            return size <= (capacity - end);
        }

        // Must check Available first or this may return an invalid address
        uintptr_t Allocate(size_t size)
        {
            uintptr_t ptr = storage + end;
            end += size;
            return ptr;
        }

        uintptr_t storage;
        size_t end;
        size_t capacity;
        ArenaChunk* next;
    };

    NONCOPYABLE(DynamicArena);
public:
    DynamicArena(size_t chunkSize) : chunkSize(chunkSize), head(NULL)
    {
        AllocateNewChunk();
    }

    ~DynamicArena()
    {
        ArenaChunk* chunk = head;
        while (chunk != NULL)
        {
            ArenaChunk* next = chunk->next;
            free(chunk);
            chunk = next;
        }
    }

    void AllocateNewChunk()
    {
        // For efficiency, do a single allocation with the ArenaChunk and its storage
        ArenaChunk* next = head;
        head = (ArenaChunk*)malloc(sizeof(ArenaChunk) + chunkSize);
        ENSURE(head);
        head->storage = sizeof(ArenaChunk) + uintptr_t(head);
        head->end = 0;
        head->capacity = chunkSize;
        head->next = next;
    }

    void* allocate(size_t size)
    {
        if (size > chunkSize)
        {
            debug_warn(L"DynamicArena cannot allocate more than chunk size");
            throw std::bad_alloc();
        }
        else if (!head->Available(size))
            AllocateNewChunk();

        return (void*)head->Allocate(size);
    }

    void deallocate(void* UNUSED(p), size_t UNUSED(size))
    {
        // ignored
    }

private:

    const size_t chunkSize;
    ArenaChunk *head;
};


}   // namespace Allocators

#endif  // #ifndef INCLUDED_ALLOCATORS_ARENA