src/compiler/translator/PoolAlloc.h

//
// Copyright (c) 2002-2010 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//

#ifndef COMPILER_TRANSLATOR_POOLALLOC_H_
#define COMPILER_TRANSLATOR_POOLALLOC_H_

#ifdef _DEBUG
#define GUARD_BLOCKS  // define to enable guard block sanity checking
#endif

//
// This header defines an allocator that can be used to efficiently
// allocate a large number of small requests for heap memory, with the
// intention that they are not individually deallocated, but rather
// collectively deallocated at one time.
//
// This simultaneously
//
// * Makes each individual allocation much more efficient; the
//     typical allocation is trivial.
// * Completely avoids the cost of doing individual deallocation.
// * Saves the trouble of tracking down and plugging a large class of leaks.
//
// Individual classes can use this allocator by supplying their own
// new and delete methods.
//
// STL containers can use this allocator by using the pool_allocator
// class as the allocator (second) template argument.
//

#include <stddef.h>
#include <string.h>
#include <vector>

// If we are using guard blocks, we must track each indivual
// allocation.  If we aren't using guard blocks, these
// never get instantiated, so won't have any impact.
//

class TAllocation
{
  public:
    TAllocation(size_t size, unsigned char *mem, TAllocation *prev = 0)
        : size(size), mem(mem), prevAlloc(prev)
    {
// Allocations are bracketed:
//    [allocationHeader][initialGuardBlock][userData][finalGuardBlock]
// This would be cleaner with if (guardBlockSize)..., but that
// makes the compiler print warnings about 0 length memsets,
// even with the if() protecting them.
#ifdef GUARD_BLOCKS
        memset(preGuard(), guardBlockBeginVal, guardBlockSize);
        memset(data(), userDataFill, size);
        memset(postGuard(), guardBlockEndVal, guardBlockSize);
#endif
    }

    void check() const
    {
        checkGuardBlock(preGuard(), guardBlockBeginVal, "before");
        checkGuardBlock(postGuard(), guardBlockEndVal, "after");
    }

    void checkAllocList() const;

    // Return total size needed to accomodate user buffer of 'size',
    // plus our tracking data.
    inline static size_t allocationSize(size_t size)
    {
        return size + 2 * guardBlockSize + headerSize();
    }

    // Offset from surrounding buffer to get to user data buffer.
    inline static unsigned char *offsetAllocation(unsigned char *m)
    {
        return m + guardBlockSize + headerSize();
    }

  private:
    void checkGuardBlock(unsigned char *blockMem, unsigned char val, const char *locText) const;

    // Find offsets to pre and post guard blocks, and user data buffer
    unsigned char *preGuard() const { return mem + headerSize(); }
    unsigned char *data() const { return preGuard() + guardBlockSize; }
    unsigned char *postGuard() const { return data() + size; }

    size_t size;             // size of the user data area
    unsigned char *mem;      // beginning of our allocation (pts to header)
    TAllocation *prevAlloc;  // prior allocation in the chain

    // Support MSVC++ 6.0
    const static unsigned char guardBlockBeginVal;
    const static unsigned char guardBlockEndVal;
    const static unsigned char userDataFill;

    const static size_t guardBlockSize;
#ifdef GUARD_BLOCKS
    inline static size_t headerSize() { return sizeof(TAllocation); }
#else
    inline static size_t headerSize() { return 0; }
#endif
};

//
// There are several stacks.  One is to track the pushing and popping
// of the user, and not yet implemented.  The others are simply a
// repositories of free pages or used pages.
//
// Page stacks are linked together with a simple header at the beginning
// of each allocation obtained from the underlying OS.  Multi-page allocations
// are returned to the OS.  Individual page allocations are kept for future
// re-use.
//
// The "page size" used is not, nor must it match, the underlying OS
// page size.  But, having it be about that size or equal to a set of
// pages is likely most optimal.
//
class TPoolAllocator
{
  public:
    TPoolAllocator(int growthIncrement = 8 * 1024, int allocationAlignment = 16);

    //
    // Don't call the destructor just to free up the memory, call pop()
    //
    ~TPoolAllocator();

    //
    // Call push() to establish a new place to pop memory too.  Does not
    // have to be called to get things started.
    //
    void push();

    //
    // Call pop() to free all memory allocated since the last call to push(),
    // or if no last call to push, frees all memory since first allocation.
    //
    void pop();

    //
    // Call popAll() to free all memory allocated.
    //
    void popAll();

    //
    // Call allocate() to actually acquire memory.  Returns 0 if no memory
    // available, otherwise a properly aligned pointer to 'numBytes' of memory.
    //
    void *allocate(size_t numBytes);

    //
    // There is no deallocate.  The point of this class is that
    // deallocation can be skipped by the user of it, as the model
    // of use is to simultaneously deallocate everything at once
    // by calling pop(), and to not have to solve memory leak problems.
    //

    // Catch unwanted allocations.
    // TODO(jmadill): Remove this when we remove the global allocator.
    void lock();
    void unlock();

  private:
    size_t alignment;  // all returned allocations will be aligned at
                       // this granularity, which will be a power of 2
    size_t alignmentMask;

#if !defined(ANGLE_TRANSLATOR_DISABLE_POOL_ALLOC)
    friend struct tHeader;

    struct tHeader
    {
        tHeader(tHeader *nextPage, size_t pageCount)
            : nextPage(nextPage),
              pageCount(pageCount)
#ifdef GUARD_BLOCKS
              ,
              lastAllocation(0)
#endif
        {
        }

        ~tHeader()
        {
#ifdef GUARD_BLOCKS
            if (lastAllocation)
                lastAllocation->checkAllocList();
#endif
        }

        tHeader *nextPage;
        size_t pageCount;
#ifdef GUARD_BLOCKS
        TAllocation *lastAllocation;
#endif
    };

    struct tAllocState
    {
        size_t offset;
        tHeader *page;
    };
    typedef std::vector<tAllocState> tAllocStack;

    // Track allocations if and only if we're using guard blocks
    void *initializeAllocation(tHeader *block, unsigned char *memory, size_t numBytes)
    {
#ifdef GUARD_BLOCKS
        new (memory) TAllocation(numBytes, memory, block->lastAllocation);
        block->lastAllocation = reinterpret_cast<TAllocation *>(memory);
#endif
        // This is optimized entirely away if GUARD_BLOCKS is not defined.
        return TAllocation::offsetAllocation(memory);
    }

    size_t pageSize;           // granularity of allocation from the OS
    size_t headerSkip;         // amount of memory to skip to make room for the
                               //      header (basically, size of header, rounded
                               //      up to make it aligned
    size_t currentPageOffset;  // next offset in top of inUseList to allocate from
    tHeader *freeList;         // list of popped memory
    tHeader *inUseList;        // list of all memory currently being used
    tAllocStack mStack;        // stack of where to allocate from, to partition pool

    int numCalls;       // just an interesting statistic
    size_t totalBytes;  // just an interesting statistic

#else  // !defined(ANGLE_TRANSLATOR_DISABLE_POOL_ALLOC)
    std::vector<std::vector<void *>> mStack;
#endif

    TPoolAllocator &operator=(const TPoolAllocator &);  // dont allow assignment operator
    TPoolAllocator(const TPoolAllocator &);             // dont allow default copy constructor
    bool mLocked;
};

//
// There could potentially be many pools with pops happening at
// different times.  But a simple use is to have a global pop
// with everyone using the same global allocator.
//
extern TPoolAllocator *GetGlobalPoolAllocator();
extern void SetGlobalPoolAllocator(TPoolAllocator *poolAllocator);

//
// This STL compatible allocator is intended to be used as the allocator
// parameter to templatized STL containers, like vector and map.
//
// It will use the pools for allocation, and not
// do any deallocation, but will still do destruction.
//
template <class T>
class pool_allocator
{
  public:
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    typedef T *pointer;
    typedef const T *const_pointer;
    typedef T &reference;
    typedef const T &const_reference;
    typedef T value_type;

    template <class Other>
    struct rebind
    {
        typedef pool_allocator<Other> other;
    };
    pointer address(reference x) const { return &x; }
    const_pointer address(const_reference x) const { return &x; }

    pool_allocator() {}

    template <class Other>
    pool_allocator(const pool_allocator<Other> &p)
    {
    }

    template <class Other>
    pool_allocator<T> &operator=(const pool_allocator<Other> &p)
    {
        return *this;
    }

#if defined(__SUNPRO_CC) && !defined(_RWSTD_ALLOCATOR)
    // libCStd on some platforms have a different allocate/deallocate interface.
    // Caller pre-bakes sizeof(T) into 'n' which is the number of bytes to be
    // allocated, not the number of elements.
    void *allocate(size_type n) { return getAllocator().allocate(n); }
    void *allocate(size_type n, const void *) { return getAllocator().allocate(n); }
    void deallocate(void *, size_type) {}
#else
    pointer allocate(size_type n)
    {
        return reinterpret_cast<pointer>(getAllocator().allocate(n * sizeof(T)));
    }
    pointer allocate(size_type n, const void *)
    {
        return reinterpret_cast<pointer>(getAllocator().allocate(n * sizeof(T)));
    }
    void deallocate(pointer, size_type) {}
#endif  // _RWSTD_ALLOCATOR

    void construct(pointer p, const T &val) { new ((void *)p) T(val); }
    void destroy(pointer p) { p->T::~T(); }

    bool operator==(const pool_allocator &rhs) const { return true; }
    bool operator!=(const pool_allocator &rhs) const { return false; }

    size_type max_size() const { return static_cast<size_type>(-1) / sizeof(T); }
    size_type max_size(int size) const { return static_cast<size_type>(-1) / size; }

    TPoolAllocator &getAllocator() const { return *GetGlobalPoolAllocator(); }
};

#endif  // COMPILER_TRANSLATOR_POOLALLOC_H_