frozenobjectheap.cpp

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

#include "common.h"
#include "frozenobjectheap.h"

// Default size to reserve for a frozen segment
#define FOH_SEGMENT_DEFAULT_SIZE (4 * 1024 * 1024)
// Size to commit on demand in that reserved space
#define FOH_COMMIT_SIZE (64 * 1024)

FrozenObjectHeapManager::FrozenObjectHeapManager():
    m_Crst(CrstFrozenObjectHeap, CRST_UNSAFE_ANYMODE),
    m_SegmentRegistrationCrst(CrstFrozenObjectHeap),
    m_CurrentSegment(nullptr)
{
}

// Allocates an object of the give size (including header) on a frozen segment.
// May return nullptr if object is too large (larger than FOH_COMMIT_SIZE)
// in such cases caller is responsible to find a more appropriate heap to allocate it

Object* FrozenObjectHeapManager::TryAllocateObject(PTR_MethodTable type, size_t objectSize,
    void(*initFunc)(Object*, void*), void* pParam)
{
    CONTRACTL
    {
        THROWS;
        MODE_COOPERATIVE;
    }
    CONTRACTL_END

#ifndef FEATURE_BASICFREEZE
    // GC is required to support frozen segments
    return nullptr;
#else // FEATURE_BASICFREEZE

    Object* obj = nullptr;
    FrozenObjectSegment* curSeg = nullptr;
    uint8_t* curSegmentCurrent = nullptr;
    size_t curSegSizeCommitted = 0;

    {
        GCX_PREEMP();
        {
            CrstHolder ch(&m_Crst);

            _ASSERT(type != nullptr);
            _ASSERT(FOH_COMMIT_SIZE >= MIN_OBJECT_SIZE);
            _ASSERT(!type->Collectible());

            // Currently we don't support frozen objects with special alignment requirements
            // TODO: We should also give up on arrays of doubles on 32-bit platforms.
            // (we currently never allocate them on frozen segments)
#ifdef FEATURE_64BIT_ALIGNMENT
            if (type->RequiresAlign8())
            {
                // Align8 objects are not supported yet
                return nullptr;
            }
#endif

            // NOTE: objectSize is expected be the full size including header
            _ASSERT(objectSize >= MIN_OBJECT_SIZE);

            if (objectSize > FOH_COMMIT_SIZE)
            {
                // The current design doesn't allow objects larger than FOH_COMMIT_SIZE and
                // since FrozenObjectHeap is just an optimization, let's not fill it with huge objects.
                return nullptr;
            }

            obj = m_CurrentSegment == nullptr ? nullptr : m_CurrentSegment->TryAllocateObject(type, objectSize);
            // obj is nullptr if the current segment is full or hasn't been allocated yet
            if (obj == nullptr)
            {
                size_t newSegmentSize = FOH_SEGMENT_DEFAULT_SIZE;
                if (m_CurrentSegment != nullptr)
                {
                    // Double the reserved size to reduce the number of frozen segments in apps with lots of frozen objects
                    // Use the same size in case if prevSegmentSize*2 operation overflows.
                    const size_t prevSegmentSize = m_CurrentSegment->m_Size;
                    newSegmentSize = max(prevSegmentSize, prevSegmentSize * 2);
                }

                m_CurrentSegment = new FrozenObjectSegment(newSegmentSize);
                m_FrozenSegments.Append(m_CurrentSegment);

                // Try again
                obj = m_CurrentSegment->TryAllocateObject(type, objectSize);

                // This time it's not expected to be null
                _ASSERT(obj != nullptr);
            }

            if (initFunc != nullptr)
            {
                initFunc(obj, pParam);
            }

            curSeg = m_CurrentSegment;
            curSegSizeCommitted = curSeg->m_SizeCommitted;
            curSegmentCurrent = curSeg->m_pCurrent;
        } // end of m_Crst lock

        // Let GC know about the new segment or changes in it.
        // We do it under a new lock because the main one (m_Crst) can be used by Profiler in a GC's thread
        // and that might cause deadlocks since RegisterFrozenSegment may stuck on GC's lock.
        {
            CrstHolder regLock(&m_SegmentRegistrationCrst);
            curSeg->RegisterOrUpdate(curSegmentCurrent, curSegSizeCommitted);
        }

    } // end of GCX_PREEMP

    PublishFrozenObject(obj);

    return obj;
#endif // !FEATURE_BASICFREEZE
}

// Reserve sizeHint bytes of memory for the given frozen segment.
// The requested size can be be ignored in case of memory pressure and FOH_SEGMENT_DEFAULT_SIZE is used instead.
FrozenObjectSegment::FrozenObjectSegment(size_t sizeHint) :
    m_pStart(nullptr),
    m_pCurrent(nullptr),
    m_pCurrentRegistered(nullptr),
    m_SizeCommitted(0),
    m_Size(sizeHint),
    m_SegmentHandle(nullptr)
{
    _ASSERT(m_Size > FOH_COMMIT_SIZE);
    _ASSERT(m_Size % FOH_COMMIT_SIZE == 0);

    void* alloc = ClrVirtualAlloc(nullptr, m_Size, MEM_RESERVE, PAGE_READWRITE);
    if (alloc == nullptr)
    {
        // Try again with the default FOH size
        if (m_Size > FOH_SEGMENT_DEFAULT_SIZE)
        {
            m_Size = FOH_SEGMENT_DEFAULT_SIZE;
            _ASSERT(m_Size > FOH_COMMIT_SIZE);
            _ASSERT(m_Size % FOH_COMMIT_SIZE == 0);
            alloc = ClrVirtualAlloc(nullptr, m_Size, MEM_RESERVE, PAGE_READWRITE);
        }

        if (alloc == nullptr)
        {
            ThrowOutOfMemory();
        }
    }

    // Commit a chunk in advance
    void* committedAlloc = ClrVirtualAlloc(alloc, FOH_COMMIT_SIZE, MEM_COMMIT, PAGE_READWRITE);
    if (committedAlloc == nullptr)
    {
        ClrVirtualFree(alloc, 0, MEM_RELEASE);
        ThrowOutOfMemory();
    }

    m_pStart = static_cast<uint8_t*>(committedAlloc);
    m_pCurrent = m_pStart + sizeof(ObjHeader);
    m_SizeCommitted = FOH_COMMIT_SIZE;

    // ClrVirtualAlloc is expected to be PageSize-aligned so we can expect
    // DATA_ALIGNMENT alignment as well
    _ASSERT(IS_ALIGNED(committedAlloc, DATA_ALIGNMENT));
}

void FrozenObjectSegment::RegisterOrUpdate(uint8_t* current, size_t sizeCommited)
{
    CONTRACTL
    {
        THROWS;
        MODE_PREEMPTIVE;
    }
    CONTRACTL_END

    if (m_pCurrentRegistered == nullptr)
    {
        segment_info si;
        si.pvMem = m_pStart;
        si.ibFirstObject = sizeof(ObjHeader);
        si.ibAllocated = (size_t)current - (size_t)si.pvMem;
        si.ibCommit = sizeCommited;
        si.ibReserved = m_Size;

        assert((size_t)current >= (size_t)si.pvMem);

        // NOTE: RegisterFrozenSegment may take a GC lock inside.
        m_SegmentHandle = GCHeapUtilities::GetGCHeap()->RegisterFrozenSegment(&si);
        if (m_SegmentHandle == nullptr)
        {
            ThrowOutOfMemory();
        }
        m_pCurrentRegistered = current;
    }
    else
    {
        if (current > m_pCurrentRegistered)
        {
            GCHeapUtilities::GetGCHeap()->UpdateFrozenSegment(
                m_SegmentHandle, current, m_pStart + sizeCommited);
            m_pCurrentRegistered = current;
        }
        else
        {
            // Some other thread already advanced it.
        }
    }
}

Object* FrozenObjectSegment::TryAllocateObject(PTR_MethodTable type, size_t objectSize)
{
    _ASSERT((m_pStart != nullptr) && (m_Size > 0));
    _ASSERT(IS_ALIGNED(m_pCurrent, DATA_ALIGNMENT));
    _ASSERT(IS_ALIGNED(objectSize, DATA_ALIGNMENT));
    _ASSERT(objectSize <= FOH_COMMIT_SIZE);
    _ASSERT(m_pCurrent >= m_pStart + sizeof(ObjHeader));

    const size_t spaceUsed = (size_t)(m_pCurrent - m_pStart);
    const size_t spaceLeft = m_Size - spaceUsed;

    _ASSERT(spaceUsed >= sizeof(ObjHeader));
    _ASSERT(spaceLeft >= sizeof(ObjHeader));

    // Test if we have a room for the given object (including extra sizeof(ObjHeader) for next object)
    if (spaceLeft - sizeof(ObjHeader) < objectSize)
    {
        return nullptr;
    }

    // Check if we need to commit a new chunk
    if (spaceUsed + objectSize + sizeof(ObjHeader) > m_SizeCommitted)
    {
        // Make sure we don't go out of bounds during this commit
        _ASSERT(m_SizeCommitted + FOH_COMMIT_SIZE <= m_Size);

        if (ClrVirtualAlloc(m_pStart + m_SizeCommitted, FOH_COMMIT_SIZE, MEM_COMMIT, PAGE_READWRITE) == nullptr)
        {
            ThrowOutOfMemory();
        }
        m_SizeCommitted += FOH_COMMIT_SIZE;
    }

    Object* object = reinterpret_cast<Object*>(m_pCurrent);
    object->SetMethodTable(type);

    m_pCurrent += objectSize;

    return object;
}

Object* FrozenObjectSegment::GetFirstObject() const
{
    if (m_pStart + sizeof(ObjHeader) == m_pCurrent)
    {
        // Segment is empty
        return nullptr;
    }
    return reinterpret_cast<Object*>(m_pStart + sizeof(ObjHeader));
}

Object* FrozenObjectSegment::GetNextObject(Object* obj) const
{
    // Input must not be null and should be within the segment
    _ASSERT(obj != nullptr);
    _ASSERT((uint8_t*)obj >= m_pStart + sizeof(ObjHeader) && (uint8_t*)obj < m_pCurrent);

    // FOH doesn't support objects with non-DATA_ALIGNMENT alignment yet.
    uint8_t* nextObj = (reinterpret_cast<uint8_t*>(obj) + ALIGN_UP(obj->GetSize(), DATA_ALIGNMENT));
    if (nextObj < m_pCurrent)
    {
        return reinterpret_cast<Object*>(nextObj);
    }

    // Current object is the last one in the segment
    return nullptr;
}