(svn r7255) -Comments added for CBlobBaseSimple, CBlobT classes

yapf/blob.hpp

@@ -3,6 +3,10 @@
 #ifndef  BLOB_HPP
 #define  BLOB_HPP
 
+/** Type-safe version of memcpy().
+ * @param d destination buffer
+ * @param s source buffer
+ * @param num_items number of items to be copied (!not number of bytes!) */
 template <class Titem_>
 FORCEINLINE void MemCpyT(Titem_* d, const Titem_* s, int num_items = 1)
 {
@@ -18,51 +22,94 @@ FORCEINLINE void MemCpyT(Titem_* d, const Titem_* s, int num_items = 1)
  *        module (DLL) where the blob was allocated
  *    - no configurable allocation policy (how big blocks should be allocated)
  *    - no extra ownership policy (i.e. 'copy on write') when blob is copied
- *    - no thread synchronization at all */
+ *    - no thread synchronization at all
+ *
+ *  Internal member layout:
+ *  1. The only class member is pointer to the first item (see union ptr_u).
+ *  2. Allocated block contains the blob header (see CHdr) followed by the raw byte data.
+ *     Always, when it allocates memory the allocated size is:
+ *                                                      sizeof(CHdr) + <data capacity>
+ *  3. Two 'virtual' members (m_size and m_max_size) are stored in the CHdr at beginning
+ *     of the alloated block.
+ *  4. The pointer (in ptr_u) points behind the header (to the first data byte).
+ *     When memory block is allocated, the sizeof(CHdr) it added to it.
+ *  5. Benefits of this layout:
+ *     - items are accessed in the simplest possible way - just dereferencing the pointer,
+ *       which is good for performance (assuming that data are accessed most often).
+ *     - sizeof(blob) is the same as the size of any other pointer
+ *  6. Drawbacks of this layout:
+ *     - the fact, that pointer to the alocated block is adjusted by sizeof(CHdr) before
+ *       it is stored can lead to several confusions:
+ *         - it is not common pattern so the implementation code is bit harder to read
+ *         - valgrind can generate warning that allocated block is lost (not accessible)
+ * */
 class CBlobBaseSimple {
 protected:
+	/** header of the allocated memory block */
 	struct CHdr {
-		int    m_size;      // actual blob size in bytes
+		int    m_size;      ///< actual blob size in bytes
-		int    m_max_size;  // maximum (allocated) size in bytes
+		int    m_max_size;  ///< maximum (allocated) size in bytes
 	};
 
+	/** type used as class member */
 	union {
-		int8   *m_pData;
+		int8   *m_pData;    ///< pointer to the first byte of data
-		CHdr   *m_pHdr_1;
+		CHdr   *m_pHdr_1;   ///< pointer just after the CHdr holding m_size and m_max_size
 	} ptr_u;
 
 public:
-	static const int Ttail_reserve = 4; // four extra bytes will be always allocated and zeroed at the end
+	static const int Ttail_reserve = 4; ///< four extra bytes will be always allocated and zeroed at the end
 
+	/** default constructor - initializes empty blob */
 	FORCEINLINE CBlobBaseSimple() { InitEmpty(); }
+	/** copy constructor */
 	FORCEINLINE CBlobBaseSimple(const CBlobBaseSimple& src)
 	{
 		InitEmpty();
 		AppendRaw(src);
 	}
+	/** destructor */
 	FORCEINLINE ~CBlobBaseSimple() { Free(); }
 protected:
+	/** initialize the empty blob by setting the ptr_u.m_pHdr_1 pointer to the static CHdr with
+	 *  both m_size and m_max_size containing zero */
 	FORCEINLINE void InitEmpty() { static CHdr hdrEmpty[] = {{0, 0}, {0, 0}}; ptr_u.m_pHdr_1 = &hdrEmpty[1]; }
+	/** initialize blob by attaching it to the given header followed by data */
 	FORCEINLINE void Init(CHdr* hdr) { ptr_u.m_pHdr_1 = &hdr[1]; }
+	/** blob header accessor - use it rather than using the pointer arithmetics directly - non-const version */
 	FORCEINLINE CHdr& Hdr() { return ptr_u.m_pHdr_1[-1]; }
+	/** blob header accessor - use it rather than using the pointer arithmetics directly - const version */
 	FORCEINLINE const CHdr& Hdr() const { return ptr_u.m_pHdr_1[-1]; }
+	/** return reference to the actual blob size - used when the size needs to be modified */
 	FORCEINLINE int& RawSizeRef() { return Hdr().m_size; };
 
 public:
+	/** return true if blob doesn't contain valid data */
 	FORCEINLINE bool IsEmpty() const { return RawSize() == 0; }
+	/** return the number of valid data bytes in the blob */
 	FORCEINLINE int RawSize() const { return Hdr().m_size; };
+	/** return the current blob capacity in bytes */
 	FORCEINLINE int MaxRawSize() const { return Hdr().m_max_size; };
+	/** return pointer to the first byte of data - non-const version */
 	FORCEINLINE int8* RawData() { return ptr_u.m_pData; }
+	/** return pointer to the first byte of data - const version */
 	FORCEINLINE const int8* RawData() const { return ptr_u.m_pData; }
 #if 0 // reenable when needed
+	/** return the 32 bit CRC of valid data in the blob */
 	FORCEINLINE uint32 Crc32() const {return CCrc32::Calc(RawData(), RawSize());}
 #endif //0
+	/** invalidate blob's data - doesn't free buffer */
 	FORCEINLINE void Clear() { RawSizeRef() = 0; }
+	/** free the blob's memory */
 	FORCEINLINE void Free() { if (MaxRawSize() > 0) {RawFree(&Hdr()); InitEmpty();} }
+	/** copy data from another blob - replaces any existing blob's data */
 	FORCEINLINE void CopyFrom(const CBlobBaseSimple& src) { Clear(); AppendRaw(src); }
+	/** overtake ownership of data buffer from the source blob - source blob will become empty */
 	FORCEINLINE void MoveFrom(CBlobBaseSimple& src) { Free(); ptr_u.m_pData = src.ptr_u.m_pData; src.InitEmpty(); }
+	/** swap buffers (with data) between two blobs (this and source blob) */
 	FORCEINLINE void Swap(CBlobBaseSimple& src) { int8 *tmp = ptr_u.m_pData; ptr_u.m_pData = src.ptr_u.m_pData; src.ptr_u.m_pData = tmp; }
 
+	/** append new bytes at the end of existing data bytes - reallocates if necessary */
 	FORCEINLINE void AppendRaw(int8 *p, int num_bytes)
 	{
 		assert(p != NULL);
@@ -73,6 +120,7 @@ public:
 		}
 	}
 
+	/** append bytes from given source blob to the end of existing data bytes - reallocates if necessary */
 	FORCEINLINE void AppendRaw(const CBlobBaseSimple& src)
 	{
 		if (!src.IsEmpty())
@@ -164,6 +212,13 @@ public:
 	}
 };
 
+/** Blob - simple dynamic Titem_ array. Titem_ (template argument) is a placeholder for any type.
+ *  Titem_ can be any integral type, pointer, or structure. Using Blob instead of just plain C array
+ *  simplifies the resource management in several ways:
+ *  1. When adding new item(s) it automatically grows capacity if needed.
+ *  2. When variable of type Blob comes out of scope it automatically frees the data buffer.
+ *  3. Takes care about the actual data size (number of used items).
+ *  4. Dynamically constructs only used items (as opposite of static array which constructs all items) */
 template <class Titem_, class Tbase_ = CBlobBaseSimple>
 class CBlobT : public CBlobBaseSimple {
 	// make template arguments public:
@@ -173,15 +228,25 @@ public:
 
 	static const int Titem_size = sizeof(Titem);
 
+	/** Default constructor - makes new Blob ready to accept any data */
 	FORCEINLINE CBlobT() : Tbase() {}
+	/** Copy constructor - make new blob to become copy of the original (source) blob */
 	FORCEINLINE CBlobT(const Tbase& src) : Tbase(src) {assert((RawSize() % Titem_size) == 0);}
+	/** Destructor - ensures that allocated memory (if any) is freed */
 	FORCEINLINE ~CBlobT() { Free(); }
+	/** Check the validity of item index (only in debug mode) */
 	FORCEINLINE void CheckIdx(int idx) { assert(idx >= 0); assert(idx < Size()); }
+	/** Return pointer to the first data item - non-const version */
 	FORCEINLINE Titem* Data() { return (Titem*)RawData(); }
+	/** Return pointer to the first data item - const version */
 	FORCEINLINE const Titem* Data() const { return (const Titem*)RawData(); }
+	/** Return pointer to the idx-th data item - non-const version */
 	FORCEINLINE Titem* Data(int idx) { CheckIdx(idx); return (Data() + idx); }
+	/** Return pointer to the idx-th data item - const version */
 	FORCEINLINE const Titem* Data(int idx) const { CheckIdx(idx); return (Data() + idx); }
+	/** Return number of items in the Blob */
 	FORCEINLINE int Size() const { return (RawSize() / Titem_size); }
+	/** Free the memory occupied by Blob destroying all items */
 	FORCEINLINE void Free()
 	{
 		assert((RawSize() % Titem_size) == 0);
@@ -193,12 +258,15 @@ public:
 		}
 		Tbase::Free();
 	}
+	/** Grow number of data items in Blob by given number - doesn't construct items */
 	FORCEINLINE Titem* GrowSizeNC(int num_items) { return (Titem*)GrowRawSize(num_items * Titem_size); }
+	/** Grow number of data items in Blob by given number - constructs new items (using Titem_'s default constructor) */
 	FORCEINLINE Titem* GrowSizeC(int num_items)
 	{
 		Titem* pI = GrowSizeNC(num_items);
 		for (int i = num_items; i > 0; i--, pI++) new (pI) Titem();
 	}
+	/** Destroy given number of items and reduce the Blob's data size */
 	FORCEINLINE void ReduceSize(int num_items)
 	{
 		assert((RawSize() % Titem_size) == 0);
@@ -211,18 +279,21 @@ public:
 		// remove them
 		ReduceRawSize(num_items * Titem_size);
 	}
+	/** Append one data item at the end (calls Titem_'s default constructor) */
 	FORCEINLINE Titem* AppendNew()
 	{
-		Titem& dst = *GrowSizeNC(1);
+		Titem& dst = *GrowSizeNC(1); // Grow size by one item
-		Titem* pNewItem = new (&dst) Titem();
+		Titem* pNewItem = new (&dst) Titem(); // construct the new item by calling in-place new operator
 		return pNewItem;
 	}
+	/** Append the copy of given item at the end of Blob (using copy constructor) */
 	FORCEINLINE Titem* Append(const Titem& src)
 	{
-		Titem& dst = *GrowSizeNC(1);
+		Titem& dst = *GrowSizeNC(1); // Grow size by one item
-		Titem* pNewItem = new (&dst) Titem(src);
+		Titem* pNewItem = new (&dst) Titem(src); // construct the new item by calling in-place new operator with copy ctor()
 		return pNewItem;
 	}
+	/** Add given items (ptr + number of items) at the end of blob */
 	FORCEINLINE Titem* Append(const Titem* pSrc, int num_items)
 	{
 		Titem* pDst = GrowSizeNC(num_items);
@@ -231,6 +302,7 @@ public:
 		while (pDst < pDstEnd) new (pDst++) Titem(*(pSrc++));
 		return pDstOrg;
 	}
+	/** Remove item with the given index by replacing it by the last item and reducing the size by one */
 	FORCEINLINE void RemoveBySwap(int idx)
 	{
 		CheckIdx(idx);
@@ -238,6 +310,7 @@ public:
 		Titem* pRemoved = Data(idx);
 		RemoveBySwap(pRemoved);
 	}
+	/** Remove item given by pointer replacing it by the last item and reducing the size by one */
 	FORCEINLINE void RemoveBySwap(Titem* pItem)
 	{
 		Titem* pLast = Data(Size() - 1);
@@ -252,6 +325,8 @@ public:
 		// and reduce the raw blob size
 		ReduceRawSize(Titem_size);
 	}
+	/** Ensures that given number of items can be added to the end of Blob. Returns pointer to the
+	 *  first free (unused) item */
 	FORCEINLINE Titem* MakeFreeSpace(int num_items) { return (Titem*)MakeRawFreeSpace(num_items * Titem_size); }
 };