memnodes.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * memnodes.h
 *    POSTGRES memory context node definitions.
 *
 *
 * Portions Copyright (c) 1996-2013, 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, int level);
#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) */
    bool        isReset;        /* T = no space alloced since last reset */
} 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 */