src/libpq/include/nodes/memnodes.h

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/*-------------------------------------------------------------------------
 *
 * memnodes.h
 *        POSTGRES memory context node definitions.
 *
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/nodes/memnodes.h,v 1.30 2004/12/31 22:03:34 pgsql Exp $
 *
 *-------------------------------------------------------------------------
 */
#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) (MemoryContext context);
        Size            (*get_chunk_space) (MemoryContext context, void *pointer);
        bool            (*is_empty) (MemoryContext context);
        void            (*stats) (MemoryContext context);
#ifdef MEMORY_CONTEXT_CHECKING
        void            (*check) (MemoryContext context);
#endif
} MemoryContextMethods;


typedef struct MemoryContextData
{
        NodeTag         type;                   /* identifies exact kind of context */
        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) */
} 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 */