rippled/modules/beast_basics/memory/beast_FifoFreeStoreWithTLS.cpp

/*============================================================================*/
/*
  VFLib: https://github.com/vinniefalco/VFLib

  Copyright (C) 2008 by Vinnie Falco <vinnie.falco@gmail.com>

  This library contains portions of other open source products covered by
  separate licenses. Please see the corresponding source files for specific
  terms.

  VFLib is provided under the terms of The MIT License (MIT):

  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.
*/
/*============================================================================*/

// Implementation notes
//
// - A Page is a large allocation from a global PageAllocator.
//
// - Each thread maintains an 'active' page from which it makes allocations.
//
// - When the active page is full, a new one takes it's place.
//
// - Page memory is deallocated when it is not active and no longer referenced.
//
// - Each instance of FifoFreeStoreWithTLS maintains its own set of per-thread active pages,
//   but uses a global PageAllocator. This reduces memory consumption without
//   affecting performance.
//

// This precedes every allocation
//
struct FifoFreeStoreWithTLS::Header
{
    FifoFreeStoreWithTLS::Page* page;
};

//------------------------------------------------------------------------------

class FifoFreeStoreWithTLS::Page : LeakChecked <Page>, Uncopyable
{
public:
    explicit Page (const size_t bytes) : m_refs (1)
    {
        m_end = reinterpret_cast <char*> (this) + bytes;
        m_free = reinterpret_cast <char*> (
                     Memory::pointerAdjustedForAlignment (this + 1));
    }

    ~Page ()
    {
        bassert (! m_refs.isSignaled ());
    }

    inline bool release ()
    {
        bassert (! m_refs.isSignaled ());

        return m_refs.release ();
    }

    void* allocate (size_t bytes)
    {
        bassert (bytes > 0);

        char* p = Memory::pointerAdjustedForAlignment (m_free);
        char* free = p + bytes;

        if (free <= m_end)
        {
            m_free = free;

            m_refs.addref ();
        }
        else
        {
            p = 0;
        }

        return p;
    }

private:
    AtomicCounter m_refs; // reference count
    char* m_free;           // next free byte
    char* m_end;            // last free byte + 1
};

//------------------------------------------------------------------------------

class FifoFreeStoreWithTLS::PerThreadData : LeakChecked <PerThreadData>, Uncopyable
{
public:
    explicit PerThreadData (FifoFreeStoreWithTLS* allocator)
        : m_allocator (*allocator)
        , m_active (m_allocator.newPage ())
    {
    }

    ~PerThreadData ()
    {
        if (m_active->release ())
            m_allocator.deletePage (m_active);
    }

    inline void* allocate (const size_t bytes)
    {
        const size_t headerBytes = Memory::sizeAdjustedForAlignment (sizeof (Header));
        const size_t bytesNeeded = headerBytes + bytes;

        if (bytesNeeded > m_allocator.m_pages->getPageBytes ())
            Throw (Error ().fail (__FILE__, __LINE__, TRANS ("the memory request was too large")));

        Header* header;

        header = reinterpret_cast <Header*> (m_active->allocate (bytesNeeded));

        if (!header)
        {
            if (m_active->release ())
                deletePage (m_active);

            m_active = m_allocator.newPage ();

            header = reinterpret_cast <Header*> (m_active->allocate (bytesNeeded));
        }

        header->page = m_active;

        return reinterpret_cast <char*> (header) + headerBytes;
    }

private:
    FifoFreeStoreWithTLS& m_allocator;
    Page* m_active;
};

//------------------------------------------------------------------------------

inline FifoFreeStoreWithTLS::Page* FifoFreeStoreWithTLS::newPage ()
{
    return new (m_pages->allocate ()) Page (m_pages->getPageBytes ());
}

inline void FifoFreeStoreWithTLS::deletePage (Page* page)
{
    // Safe, because each thread maintains its own active page.
    page->~Page ();
    PagedFreeStoreType::deallocate (page);
}

FifoFreeStoreWithTLS::FifoFreeStoreWithTLS ()
    : m_pages (PagedFreeStoreType::getInstance ())
{
    //bassert (m_pages->getPageBytes () >= sizeof (Page) + Memory::allocAlignBytes);
}

FifoFreeStoreWithTLS::~FifoFreeStoreWithTLS ()
{
    // Clean up this thread's data before we release
    // the reference to the global page allocator.
    m_tsp.reset (0);
}

//------------------------------------------------------------------------------

void* FifoFreeStoreWithTLS::allocate (const size_t bytes)
{
    PerThreadData* data = m_tsp.get ();

    if (!data)
    {
        data = new PerThreadData (this);
        m_tsp.reset (data);
    }

    return data->allocate (bytes);
}

//------------------------------------------------------------------------------

void FifoFreeStoreWithTLS::deallocate (void* p)
{
    const size_t headerBytes = Memory::sizeAdjustedForAlignment (sizeof (Header));
    Header* const header = reinterpret_cast <Header*> (reinterpret_cast <char*> (p) - headerBytes);
    Page* const page = header->page;

    if (page->release ())
        deletePage (page);
}