memnodes.h

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/*-------------------------------------------------------------------------
 *
 * memnodes.h
 *    POSTGRES memory context node definitions.
 *
 *
 * Portions Copyright (c) 1996-2025, 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"
 
/*
 * MemoryContextCounters
 *      Summarization state for MemoryContextStats collection.
 *
 * The set of counters in this struct is biased towards AllocSet; if we ever
 * add any context types that are based on fundamentally different approaches,
 * we might need more or different counters here.  A possible API spec then
 * would be to print only nonzero counters, but for now we just summarize in
 * the format historically used by AllocSet.
 */
typedef struct MemoryContextCounters
{
    Size        nblocks;        /* Total number of malloc blocks */
    Size        freechunks;     /* Total number of free chunks */
    Size        totalspace;     /* Total bytes requested from malloc */
    Size        freespace;      /* The unused portion of totalspace */
} MemoryContextCounters;
 
/*
 * MemoryContext
 *      A logical context in which memory allocations occur.
 *
 * MemoryContext itself is an abstract type that can have multiple
 * implementations.
 * 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 MemoryContextData.
 *
 * Note: for largely historical reasons, typedef MemoryContext is a pointer
 * to the context struct rather than the struct type itself.
 */
 
typedef void (*MemoryStatsPrintFunc) (MemoryContext context, void *passthru,
                                      const char *stats_string,
                                      bool print_to_stderr);
 
typedef struct MemoryContextMethods
{
    /*
     * Function to handle memory allocation requests of 'size' to allocate
     * memory into the given 'context'.  The function must handle flags
     * MCXT_ALLOC_HUGE and MCXT_ALLOC_NO_OOM.  MCXT_ALLOC_ZERO is handled by
     * the calling function.
     */
    void       *(*alloc) (MemoryContext context, Size size, int flags);
 
    /* call this free_p in case someone #define's free() */
    void        (*free_p) (void *pointer);
 
    /*
     * Function to handle a size change request for an existing allocation.
     * The implementation must handle flags MCXT_ALLOC_HUGE and
     * MCXT_ALLOC_NO_OOM.  MCXT_ALLOC_ZERO is handled by the calling function.
     */
    void       *(*realloc) (void *pointer, Size size, int flags);
 
    /*
     * Invalidate all previous allocations in the given memory context and
     * prepare the context for a new set of allocations.  Implementations may
     * optionally free() excess memory back to the OS during this time.
     */
    void        (*reset) (MemoryContext context);
 
    /* Free all memory consumed by the given MemoryContext. */
    void        (*delete_context) (MemoryContext context);
 
    /* Return the MemoryContext that the given pointer belongs to. */
    MemoryContext (*get_chunk_context) (void *pointer);
 
    /*
     * Return the number of bytes consumed by the given pointer within its
     * memory context, including the overhead of alignment and chunk headers.
     */
    Size        (*get_chunk_space) (void *pointer);
 
    /*
     * Return true if the given MemoryContext has not had any allocations
     * since it was created or last reset.
     */
    bool        (*is_empty) (MemoryContext context);
    void        (*stats) (MemoryContext context,
                          MemoryStatsPrintFunc printfunc, void *passthru,
                          MemoryContextCounters *totals,
                          bool print_to_stderr);
#ifdef MEMORY_CONTEXT_CHECKING
 
    /*
     * Perform validation checks on the given context and raise any discovered
     * anomalies as WARNINGs.
     */
    void        (*check) (MemoryContext context);
#endif
} MemoryContextMethods;
 
 
typedef struct MemoryContextData
{
    pg_node_attr(abstract)      /* there are no nodes of this type */
 
    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 */
    Size        mem_allocated;  /* track memory allocated for this context */
    const MemoryContextMethods *methods;    /* virtual function table */
    MemoryContext parent;       /* NULL if no parent (toplevel context) */
    MemoryContext firstchild;   /* head of linked list of children */
    MemoryContext prevchild;    /* previous child of same parent */
    MemoryContext nextchild;    /* next child of same parent */
    const char *name;           /* context name */
    const char *ident;          /* context ID if any */
    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) || \
      IsA((context), SlabContext) || \
      IsA((context), GenerationContext) || \
      IsA((context), BumpContext)))
 
#endif                          /* MEMNODES_H */