// Copyright 2016 The SwiftShader Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef _POOLALLOC_INCLUDED_
#define _POOLALLOC_INCLUDED_

#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.
	//

protected:
	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 alignment;       // all returned allocations will be aligned at
							// this granularity, which will be a power of 2
	size_t alignmentMask;
	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 stack;      // stack of where to allocate from, to partition pool

	int numCalls;           // just an interesting statistic
	size_t totalBytes;      // just an interesting statistic
private:
	TPoolAllocator& operator=(const TPoolAllocator&);  // dont allow assignment operator
	TPoolAllocator(const TPoolAllocator&);  // dont allow default copy constructor
};


//
// 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() : allocator(GetGlobalPoolAllocator()) { }
	pool_allocator(TPoolAllocator& a) : allocator(&a) { }
	pool_allocator(const pool_allocator<T>& p) : allocator(p.allocator) { }

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

	template<class Other>
	pool_allocator(const pool_allocator<Other>& p) : allocator(&p.getAllocator()) { }

#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 &getAllocator() == &rhs.getAllocator(); }
	bool operator!=(const pool_allocator& rhs) const { return &getAllocator() != &rhs.getAllocator(); }

	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; }

	void setAllocator(TPoolAllocator *a) { allocator = a; }
	TPoolAllocator& getAllocator() const { return *allocator; }

protected:
	TPoolAllocator *allocator;
};

#endif // _POOLALLOC_INCLUDED_