text: /*-------------------------------------------------------------------------
   *
   * memnodes.h
   *	  POSTGRES memory context node definitions.
   *
   *
   * Portions Copyright (c) 2007-2008, Greenplum inc
   * Portions Copyright (c) 2012-Present Pivotal Software, Inc.
   * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/nodes/memnodes.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef MEMNODES_H
  #define MEMNODES_H
  
  #include "nodes/nodes.h"
  
  /*
   * MemoryContext
   *		A logical context in which memory allocations occur.
   *
   * MemoryContext itself is an abstract type that can have multiple
   * implementations, though for now we have only AllocSetContext.
   * The function pointers in MemoryContextMethods define one specific
   * implementation of MemoryContext --- they are a virtual function table
   * in C++ terms.
   *
   * Node types that are actual implementations of memory contexts must
   * begin with the same fields as MemoryContext.
   *
   * Note: for largely historical reasons, typedef MemoryContext is a pointer
   * to the context struct rather than the struct type itself.
   */
  
  typedef struct MemoryContextMethods
  {
  	void	   *(*alloc) (MemoryContext context, Size size);
  	/* call this free_p in case someone #define's free() */
  	void		(*free_p) (MemoryContext context, void *pointer);
  	void	   *(*realloc) (MemoryContext context, void *pointer, Size size);
  	void		(*init) (MemoryContext context);
  	void		(*reset) (MemoryContext context);
  	void		(*delete_context) (MemoryContext context);
  	Size		(*get_chunk_space) (MemoryContext context, void *pointer);
  	bool		(*is_empty) (MemoryContext context);
  	void		(*stats) (MemoryContext context, uint64 *nBlocks, uint64 *nChunks, uint64 *currentAvailable, uint64 *allAllocated, uint64 *allFreed, uint64 *maxHeld);
  	void		(*release_accounting)(MemoryContext context);
  #ifdef MEMORY_CONTEXT_CHECKING
  	void		(*check) (MemoryContext context);
  #endif
  } MemoryContextMethods;
  
  
  typedef struct MemoryContextData
  {
  	NodeTag		type;			/* identifies exact kind of context */
  	/* these two fields are placed here to minimize alignment wastage: */
  	bool		isReset;		/* T = no space alloced since last reset */
  	bool		allowInCritSection;		/* allow palloc in critical section */
  	MemoryContextMethods methods;		/* virtual function table */
  	MemoryContext parent;		/* NULL if no parent (toplevel context) */
  	MemoryContext firstchild;	/* head of linked list of children */
  	MemoryContext nextchild;	/* next child of same parent */
  	char	   *name;			/* context name (just for debugging) */
      /* CDB: Lifetime cumulative stats for this context and all descendants */
      uint64      allBytesAlloc;  /* bytes allocated from lower level mem mgr */
      uint64      allBytesFreed;  /* bytes returned to lower level mem mgr */
      Size        maxBytesHeld;   /* high-water mark for total bytes held */
      Size        localMinHeld;   /* low-water mark since last increase in hwm */
  #ifdef CDB_PALLOC_CALLER_ID
      const char *callerFile;     /* __FILE__ of most recent caller */
      int         callerLine;     /* __LINE__ of most recent caller */
  #endif
  	MemoryContextCallback *reset_cbs;	/* list of reset/delete callbacks */
  } MemoryContextData;
  
  /* utils/palloc.h contains typedef struct MemoryContextData *MemoryContext */
  
  
  /*
   * MemoryContextIsValid
   *		True iff memory context is valid.
   *
   * Add new context types to the set accepted by this macro.
   */
  #define MemoryContextIsValid(context) \
  	((context) != NULL && \
  	 (IsA((context), AllocSetContext)))
  
  #endif   /* MEMNODES_H */
  