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MemArena max pending free is now a template parameter
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VMemVector is much smaller now thanks to this (40 bytes instead of 144) since it doesn't need to support out of order frees.
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@jlaumon
jlaumon committed Dec 15, 2024
1 parent 9a23140 commit 2a498d9
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Showing 8 changed files with 223 additions and 158 deletions.
42 changes: 26 additions & 16 deletions Bedrock/Allocator.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,13 +33,14 @@ struct TempAllocator
};



// Allocates from an externally provided MemArena.
template <typename taType>
struct ArenaAllocator
template <typename taType, int taMaxPendingFrees>
struct ArenaAllocatorBase
{
ArenaAllocator() = default;
ArenaAllocator(MemArena& inArena) : mArena(&inArena) {}
using MemArenaType = MemArena<taMaxPendingFrees>;

ArenaAllocatorBase() = default;
ArenaAllocatorBase(MemArenaType& inArena) : mArena(&inArena) {}

// Allocate memory.
taType* Allocate(int inSize) { return (taType*)mArena->Alloc(inSize * sizeof(taType)).mPtr; }
Expand All @@ -48,22 +49,28 @@ struct ArenaAllocator
// Try changing the size of an existing allocation, return false if unsuccessful.
bool TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize);

MemArena* GetArena() { return mArena; }
const MemArena* GetArena() const { return mArena; }
MemArenaType* GetArena() { return mArena; }
const MemArenaType* GetArena() const { return mArena; }

private:
MemArena* mArena = nullptr;
MemArenaType* mArena = nullptr;
};

// Shorter version with default number of allowed out of order frees.
// This alias is needed because containers only accept alloctor with a single template parameter.
template <typename taType>
using ArenaAllocator = ArenaAllocatorBase<taType, cDefaultMaxPendingFrees>;


// Allocates from an internal VMemArena which uses virtual memory.
// The VMemArena can grow as necessary by committing more virtual memory.
template <typename taType>
struct VMemAllocator
{
static constexpr int64 cDefaultReservedSize = VMemArena::cDefaultReservedSize; // By default the arena will reserve that much virtual memory.
static constexpr int64 cDefaultCommitSize = VMemArena::cDefaultCommitSize; // By default the arena will commit that much virtual memory every time it grows.
using VMemArenaType = VMemArena<0>; // Don't need to support any out of order free since the arena isn't shared.

static constexpr int64 cDefaultReservedSize = VMemArenaType::cDefaultReservedSize; // By default the arena will reserve that much virtual memory.
static constexpr int64 cDefaultCommitSize = VMemArenaType::cDefaultCommitSize; // By default the arena will commit that much virtual memory every time it grows.

VMemAllocator() = default;
VMemAllocator(int inReserveSizeInBytes, int inCommitIncreaseSizeInBytes = cDefaultCommitSize)
Expand All @@ -77,7 +84,7 @@ struct VMemAllocator
bool TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize);

private:
VMemArena mArena;
VMemArenaType mArena;
};


Expand Down Expand Up @@ -118,8 +125,8 @@ bool TempAllocator<taType>::TryRealloc(taType* inPtr, int inCurrentSize, int inN
}


template <typename taType> bool
ArenaAllocator<taType>::TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize)
template <typename taType, int taMaxPendingFrees>
bool ArenaAllocatorBase<taType, taMaxPendingFrees>::TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize)
{
gAssert(inPtr != nullptr); // Call Allocate instead.

Expand All @@ -128,17 +135,20 @@ ArenaAllocator<taType>::TryRealloc(taType* inPtr, int inCurrentSize, int inNewSi
}


template <typename taType> taType* VMemAllocator<taType>::Allocate(int inSize)
template <typename taType>
taType* VMemAllocator<taType>::Allocate(int inSize)
{
// If the arena wasn't initialized yet, do it now (with default values).
// It's better to do it lazily than reserving virtual memory in every container default constructor.
if (mArena.GetMemBlock() == nullptr) [[unlikely]]
mArena = VMemArena(cDefaultReservedSize, cDefaultCommitSize);
mArena = VMemArenaType(cDefaultReservedSize, cDefaultCommitSize);

return (taType*)mArena.Alloc(inSize * sizeof(taType)).mPtr;
}

template <typename taType> bool VMemAllocator<taType>::TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize)

template <typename taType>
bool VMemAllocator<taType>::TryRealloc(taType* inPtr, int inCurrentSize, int inNewSize)
{
gAssert(inPtr != nullptr); // Call Allocate instead.

Expand Down
9 changes: 8 additions & 1 deletion Bedrock/Assert.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,5 +33,12 @@ bool gReportAssert(const char* inCondition, const char* inFile, int inLine)
return true;
}

#endif

#endif

void gCrash(const char* inMessage)
{
gTrace("%s", inMessage);

CRASH;
}
20 changes: 15 additions & 5 deletions Bedrock/Assert.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,18 @@
#pragma once

// Break to the debugger (or crash if no debugger is attached).
#define breakpoint __debugbreak()
#define BREAKPOINT __debugbreak()

// Cause a crash.
#ifdef __clang__
#define CRASH __builtin_trap()
#elif _MSC_VER
extern "C" void __ud2();
#define CRASH __ud2()
#else
#error Unknown compiler
#endif


#ifdef ASSERTS_ENABLED

Expand All @@ -11,7 +22,7 @@
do \
{ \
if (!(condition) && gReportAssert(#condition, __FILE__, __LINE__)) [[unlikely]] \
breakpoint; \
BREAKPOINT; \
} while (0)

// Internal assert report function. Return true if it should break.
Expand All @@ -27,6 +38,5 @@ bool gReportAssert(const char* inCondition, const char* inFile, int inLine);
#define gBoundsCheck(index, size) gAssert((index) >= 0 && (index) < (size))


// Force a crash.
// TODO: This needs to be improved. Do something with the message, do a proper crash instead of a breakpoint.
[[noreturn]] inline void gCrash(const char* inMessage) { breakpoint; }
// Print a message then crash.
[[noreturn]] void gCrash(const char* inMessage);
100 changes: 1 addition & 99 deletions Bedrock/MemoryArena.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2,109 +2,11 @@
#include <Bedrock/MemoryArena.h>
#include <Bedrock/Test.h>

void MemArena::AddPendingFree(FreeBlock inFreeBlock)
{
for (int i = 0; i < mNumPendingFrees; i++)
{
if (inFreeBlock.mEndOffset < mPendingFrees[i].BeginOffset())
{
// Inserting before.
if (mNumPendingFrees == cMaxPendingFrees) [[unlikely]]
gCrash("MemArena: too many out of order frees");

// Move all the blocks towards the back to make room.
gMemMove(&mPendingFrees[i + 1], &mPendingFrees[i], sizeof(FreeBlock) * (mNumPendingFrees - i));

// Place the new block.
mPendingFrees[i] = inFreeBlock;
mNumPendingFrees++;

return;
}

if (inFreeBlock.mEndOffset == mPendingFrees[i].BeginOffset())
{
// Inserting just before, merge instead.
mPendingFrees[i].mSize += inFreeBlock.mSize;

return;
}

if (inFreeBlock.BeginOffset() == mPendingFrees[i].mEndOffset)
{
// Inserting just after, merge instead.
mPendingFrees[i].mEndOffset = inFreeBlock.mEndOffset;
mPendingFrees[i].mSize += inFreeBlock.mSize;

// Check if the next block can be merged as well now.
if ((i + 1) < mNumPendingFrees)
{
if (mPendingFrees[i].mEndOffset == mPendingFrees[i + 1].BeginOffset())
{
// Merge the next block.
mPendingFrees[i].mEndOffset = mPendingFrees[i + 1].mEndOffset;
mPendingFrees[i].mSize += mPendingFrees[i + 1].mSize;

// Move all the following blocks towards the front to fill the gap.
gMemMove(&mPendingFrees[i + 1], &mPendingFrees[i + 2], sizeof(FreeBlock) * (mNumPendingFrees - 2 - i));
mNumPendingFrees--;
}
}

return;
}
}

// Otherwise add it at the back of the list.
if (mNumPendingFrees == cMaxPendingFrees)
gCrash("MemArena: too many out of order frees");

mPendingFrees[mNumPendingFrees] = inFreeBlock;
mNumPendingFrees++;
}


void MemArena::TryRemovePendingFrees()
{
if (mNumPendingFrees == 0)
return;

// Pending blocks are sorted and coalesced, so we only need to check the last one.
if (mPendingFrees[mNumPendingFrees - 1].mEndOffset == mCurrentOffset)
{
// Free it.
mCurrentOffset -= mPendingFrees[mNumPendingFrees - 1].mSize;
mNumPendingFrees--;
}
}


VMemArena::~VMemArena()
{
FreeReserved();
}

void VMemArena::CommitMore(int inNewEndOffset)
{
gAssert(inNewEndOffset > mEndOffset);

int64 commit_size = gMax(mCommitIncreaseSize, (inNewEndOffset - mEndOffset));
MemBlock committed_mem = gVMemCommit({ mBeginPtr + mEndOffset, commit_size });

mEndOffset = (int)(committed_mem.mPtr + committed_mem.mSize - mBeginPtr);
}

void VMemArena::FreeReserved()
{
if (mBeginPtr != nullptr)
gVMemFree({ mBeginPtr, mEndReservedOffset });
}



REGISTER_TEST("MemArena")
{
alignas(MemArena::cAlignment) uint8 buffer[MemArena::cAlignment * 5];
alignas(MemArena<>::cAlignment) uint8 buffer[MemArena<>::cAlignment * 5];
MemArena arena({ buffer, sizeof(buffer) });

MemBlock b1 = arena.Alloc(1);
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