mcxt.c

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/*-------------------------------------------------------------------------
 *
 * mcxt.c
 *    POSTGRES memory context management code.
 *
 * This module handles context management operations that are independent
 * of the particular kind of context being operated on.  It calls
 * context-type-specific operations via the function pointers in a
 * context's MemoryContextMethods struct.
 *
 * A note about Valgrind support: when USE_VALGRIND is defined, we provide
 * support for memory leak tracking at the allocation-unit level.  Valgrind
 * does leak detection by tracking allocated "chunks", which can be grouped
 * into "pools".  The "chunk" terminology is overloaded, since we use that
 * word for our allocation units, and it's sometimes important to distinguish
 * those from the Valgrind objects that describe them.  To reduce confusion,
 * let's use the terms "vchunk" and "vpool" for the Valgrind objects.
 *
 * We use a separate vpool for each memory context.  The context-type-specific
 * code is responsible for creating and deleting the vpools, and also for
 * creating vchunks to cover its management data structures such as block
 * headers.  (There must be a vchunk that includes every pointer we want
 * Valgrind to consider for leak-tracking purposes.)  This module creates
 * and deletes the vchunks that cover the caller-visible allocated chunks.
 * However, the context-type-specific code must handle cleaning up those
 * vchunks too during memory context reset operations.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/mmgr/mcxt.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "utils/memdebug.h"
#include "utils/memutils.h"
#include "utils/memutils_internal.h"
#include "utils/memutils_memorychunk.h"
 
 
static void BogusFree(void *pointer);
static void *BogusRealloc(void *pointer, Size size, int flags);
static MemoryContext BogusGetChunkContext(void *pointer);
static Size BogusGetChunkSpace(void *pointer);
 
/*****************************************************************************
 *    GLOBAL MEMORY                                                          *
 *****************************************************************************/
#define BOGUS_MCTX(id) \
    [id].free_p = BogusFree, \
    [id].realloc = BogusRealloc, \
    [id].get_chunk_context = BogusGetChunkContext, \
    [id].get_chunk_space = BogusGetChunkSpace
 
static const MemoryContextMethods mcxt_methods[] = {
    /* aset.c */
    [MCTX_ASET_ID].alloc = AllocSetAlloc,
    [MCTX_ASET_ID].free_p = AllocSetFree,
    [MCTX_ASET_ID].realloc = AllocSetRealloc,
    [MCTX_ASET_ID].reset = AllocSetReset,
    [MCTX_ASET_ID].delete_context = AllocSetDelete,
    [MCTX_ASET_ID].get_chunk_context = AllocSetGetChunkContext,
    [MCTX_ASET_ID].get_chunk_space = AllocSetGetChunkSpace,
    [MCTX_ASET_ID].is_empty = AllocSetIsEmpty,
    [MCTX_ASET_ID].stats = AllocSetStats,
#ifdef MEMORY_CONTEXT_CHECKING
    [MCTX_ASET_ID].check = AllocSetCheck,
#endif
 
    /* generation.c */
    [MCTX_GENERATION_ID].alloc = GenerationAlloc,
    [MCTX_GENERATION_ID].free_p = GenerationFree,
    [MCTX_GENERATION_ID].realloc = GenerationRealloc,
    [MCTX_GENERATION_ID].reset = GenerationReset,
    [MCTX_GENERATION_ID].delete_context = GenerationDelete,
    [MCTX_GENERATION_ID].get_chunk_context = GenerationGetChunkContext,
    [MCTX_GENERATION_ID].get_chunk_space = GenerationGetChunkSpace,
    [MCTX_GENERATION_ID].is_empty = GenerationIsEmpty,
    [MCTX_GENERATION_ID].stats = GenerationStats,
#ifdef MEMORY_CONTEXT_CHECKING
    [MCTX_GENERATION_ID].check = GenerationCheck,
#endif
 
    /* slab.c */
    [MCTX_SLAB_ID].alloc = SlabAlloc,
    [MCTX_SLAB_ID].free_p = SlabFree,
    [MCTX_SLAB_ID].realloc = SlabRealloc,
    [MCTX_SLAB_ID].reset = SlabReset,
    [MCTX_SLAB_ID].delete_context = SlabDelete,
    [MCTX_SLAB_ID].get_chunk_context = SlabGetChunkContext,
    [MCTX_SLAB_ID].get_chunk_space = SlabGetChunkSpace,
    [MCTX_SLAB_ID].is_empty = SlabIsEmpty,
    [MCTX_SLAB_ID].stats = SlabStats,
#ifdef MEMORY_CONTEXT_CHECKING
    [MCTX_SLAB_ID].check = SlabCheck,
#endif
 
    /* alignedalloc.c */
    [MCTX_ALIGNED_REDIRECT_ID].alloc = NULL,    /* not required */
    [MCTX_ALIGNED_REDIRECT_ID].free_p = AlignedAllocFree,
    [MCTX_ALIGNED_REDIRECT_ID].realloc = AlignedAllocRealloc,
    [MCTX_ALIGNED_REDIRECT_ID].reset = NULL,    /* not required */
    [MCTX_ALIGNED_REDIRECT_ID].delete_context = NULL,   /* not required */
    [MCTX_ALIGNED_REDIRECT_ID].get_chunk_context = AlignedAllocGetChunkContext,
    [MCTX_ALIGNED_REDIRECT_ID].get_chunk_space = AlignedAllocGetChunkSpace,
    [MCTX_ALIGNED_REDIRECT_ID].is_empty = NULL, /* not required */
    [MCTX_ALIGNED_REDIRECT_ID].stats = NULL,    /* not required */
#ifdef MEMORY_CONTEXT_CHECKING
    [MCTX_ALIGNED_REDIRECT_ID].check = NULL,    /* not required */
#endif
 
    /* bump.c */
    [MCTX_BUMP_ID].alloc = BumpAlloc,
    [MCTX_BUMP_ID].free_p = BumpFree,
    [MCTX_BUMP_ID].realloc = BumpRealloc,
    [MCTX_BUMP_ID].reset = BumpReset,
    [MCTX_BUMP_ID].delete_context = BumpDelete,
    [MCTX_BUMP_ID].get_chunk_context = BumpGetChunkContext,
    [MCTX_BUMP_ID].get_chunk_space = BumpGetChunkSpace,
    [MCTX_BUMP_ID].is_empty = BumpIsEmpty,
    [MCTX_BUMP_ID].stats = BumpStats,
#ifdef MEMORY_CONTEXT_CHECKING
    [MCTX_BUMP_ID].check = BumpCheck,
#endif
 
 
    /*
     * Reserved and unused IDs should have dummy entries here.  This allows us
     * to fail cleanly if a bogus pointer is passed to pfree or the like.  It
     * seems sufficient to provide routines for the methods that might get
     * invoked from inspection of a chunk (see MCXT_METHOD calls below).
     */
    BOGUS_MCTX(MCTX_1_RESERVED_GLIBC_ID),
    BOGUS_MCTX(MCTX_2_RESERVED_GLIBC_ID),
    BOGUS_MCTX(MCTX_8_UNUSED_ID),
    BOGUS_MCTX(MCTX_9_UNUSED_ID),
    BOGUS_MCTX(MCTX_10_UNUSED_ID),
    BOGUS_MCTX(MCTX_11_UNUSED_ID),
    BOGUS_MCTX(MCTX_12_UNUSED_ID),
    BOGUS_MCTX(MCTX_13_UNUSED_ID),
    BOGUS_MCTX(MCTX_14_UNUSED_ID),
    BOGUS_MCTX(MCTX_0_RESERVED_UNUSEDMEM_ID),
    BOGUS_MCTX(MCTX_15_RESERVED_WIPEDMEM_ID)
};
 
#undef BOGUS_MCTX
 
/*
 * CurrentMemoryContext
 *      Default memory context for allocations.
 */
MemoryContext CurrentMemoryContext = NULL;
 
/*
 * Standard top-level contexts. For a description of the purpose of each
 * of these contexts, refer to src/backend/utils/mmgr/README
 */
MemoryContext TopMemoryContext = NULL;
MemoryContext ErrorContext = NULL;
MemoryContext PostmasterContext = NULL;
MemoryContext CacheMemoryContext = NULL;
MemoryContext MessageContext = NULL;
MemoryContext TopTransactionContext = NULL;
MemoryContext CurTransactionContext = NULL;
 
/* This is a transient link to the active portal's memory context: */
MemoryContext PortalContext = NULL;
 
/* Is memory context logging currently in progress? */
static bool LogMemoryContextInProgress = false;
 
static void MemoryContextDeleteOnly(MemoryContext context);
static void MemoryContextCallResetCallbacks(MemoryContext context);
static void MemoryContextStatsInternal(MemoryContext context, int level,
                                       int max_level, int max_children,
                                       MemoryContextCounters *totals,
                                       bool print_to_stderr);
static void MemoryContextStatsPrint(MemoryContext context, void *passthru,
                                    const char *stats_string,
                                    bool print_to_stderr);
 
/*
 * You should not do memory allocations within a critical section, because
 * an out-of-memory error will be escalated to a PANIC. To enforce that
 * rule, the allocation functions Assert that.
 */
#define AssertNotInCriticalSection(context) \
    Assert(CritSectionCount == 0 || (context)->allowInCritSection)
 
/*
 * Call the given function in the MemoryContextMethods for the memory context
 * type that 'pointer' belongs to.
 */
#define MCXT_METHOD(pointer, method) \
    mcxt_methods[GetMemoryChunkMethodID(pointer)].method
 
/*
 * GetMemoryChunkMethodID
 *      Return the MemoryContextMethodID from the uint64 chunk header which
 *      directly precedes 'pointer'.
 */
static inline MemoryContextMethodID
GetMemoryChunkMethodID(const void *pointer)
{
    uint64      header;
 
    /*
     * Try to detect bogus pointers handed to us, poorly though we can.
     * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
     * allocated chunk.
     */
    Assert(pointer == (const void *) MAXALIGN(pointer));
 
    /* Allow access to the uint64 header */
    VALGRIND_MAKE_MEM_DEFINED((char *) pointer - sizeof(uint64), sizeof(uint64));
 
    header = *((const uint64 *) ((const char *) pointer - sizeof(uint64)));
 
    /* Disallow access to the uint64 header */
    VALGRIND_MAKE_MEM_NOACCESS((char *) pointer - sizeof(uint64), sizeof(uint64));
 
    return (MemoryContextMethodID) (header & MEMORY_CONTEXT_METHODID_MASK);
}
 
/*
 * GetMemoryChunkHeader
 *      Return the uint64 chunk header which directly precedes 'pointer'.
 *
 * This is only used after GetMemoryChunkMethodID, so no need for error checks.
 */
static inline uint64
GetMemoryChunkHeader(const void *pointer)
{
    uint64      header;
 
    /* Allow access to the uint64 header */
    VALGRIND_MAKE_MEM_DEFINED((char *) pointer - sizeof(uint64), sizeof(uint64));
 
    header = *((const uint64 *) ((const char *) pointer - sizeof(uint64)));
 
    /* Disallow access to the uint64 header */
    VALGRIND_MAKE_MEM_NOACCESS((char *) pointer - sizeof(uint64), sizeof(uint64));
 
    return header;
}
 
/*
 * MemoryContextTraverseNext
 *      Helper function to traverse all descendants of a memory context
 *      without recursion.
 *
 * Recursion could lead to out-of-stack errors with deep context hierarchies,
 * which would be unpleasant in error cleanup code paths.
 *
 * To process 'context' and all its descendants, use a loop like this:
 *
 *     <process 'context'>
 *     for (MemoryContext curr = context->firstchild;
 *          curr != NULL;
 *          curr = MemoryContextTraverseNext(curr, context))
 *     {
 *         <process 'curr'>
 *     }
 *
 * This visits all the contexts in pre-order, that is a node is visited
 * before its children.
 */
static MemoryContext
MemoryContextTraverseNext(MemoryContext curr, MemoryContext top)
{
    /* After processing a node, traverse to its first child if any */
    if (curr->firstchild != NULL)
        return curr->firstchild;
 
    /*
     * After processing a childless node, traverse to its next sibling if
     * there is one.  If there isn't, traverse back up to the parent (which
     * has already been visited, and now so have all its descendants).  We're
     * done if that is "top", otherwise traverse to its next sibling if any,
     * otherwise repeat moving up.
     */
    while (curr->nextchild == NULL)
    {
        curr = curr->parent;
        if (curr == top)
            return NULL;
    }
    return curr->nextchild;
}
 
/*
 * Support routines to trap use of invalid memory context method IDs
 * (from calling pfree or the like on a bogus pointer).  As a possible
 * aid in debugging, we report the header word along with the pointer
 * address (if we got here, there must be an accessible header word).
 */
static void
BogusFree(void *pointer)
{
    elog(ERROR, "pfree called with invalid pointer %p (header 0x%016" PRIx64 ")",
         pointer, GetMemoryChunkHeader(pointer));
}
 
static void *
BogusRealloc(void *pointer, Size size, int flags)
{
    elog(ERROR, "repalloc called with invalid pointer %p (header 0x%016" PRIx64 ")",
         pointer, GetMemoryChunkHeader(pointer));
    return NULL;                /* keep compiler quiet */
}
 
static MemoryContext
BogusGetChunkContext(void *pointer)
{
    elog(ERROR, "GetMemoryChunkContext called with invalid pointer %p (header 0x%016" PRIx64 ")",
         pointer, GetMemoryChunkHeader(pointer));
    return NULL;                /* keep compiler quiet */
}
 
static Size
BogusGetChunkSpace(void *pointer)
{
    elog(ERROR, "GetMemoryChunkSpace called with invalid pointer %p (header 0x%016" PRIx64 ")",
         pointer, GetMemoryChunkHeader(pointer));
    return 0;                   /* keep compiler quiet */
}
 
 
/*****************************************************************************
 *    EXPORTED ROUTINES                                                      *
 *****************************************************************************/
 
 
/*
 * MemoryContextInit
 *      Start up the memory-context subsystem.
 *
 * This must be called before creating contexts or allocating memory in
 * contexts.  TopMemoryContext and ErrorContext are initialized here;
 * other contexts must be created afterwards.
 *
 * In normal multi-backend operation, this is called once during
 * postmaster startup, and not at all by individual backend startup
 * (since the backends inherit an already-initialized context subsystem
 * by virtue of being forked off the postmaster).  But in an EXEC_BACKEND
 * build, each process must do this for itself.
 *
 * In a standalone backend this must be called during backend startup.
 */
void
MemoryContextInit(void)
{
    Assert(TopMemoryContext == NULL);
 
    /*
     * First, initialize TopMemoryContext, which is the parent of all others.
     */
    TopMemoryContext = AllocSetContextCreate((MemoryContext) NULL,
                                             "TopMemoryContext",
                                             ALLOCSET_DEFAULT_SIZES);
 
    /*
     * Not having any other place to point CurrentMemoryContext, make it point
     * to TopMemoryContext.  Caller should change this soon!
     */
    CurrentMemoryContext = TopMemoryContext;
 
    /*
     * Initialize ErrorContext as an AllocSetContext with slow growth rate ---
     * we don't really expect much to be allocated in it. More to the point,
     * require it to contain at least 8K at all times. This is the only case
     * where retained memory in a context is *essential* --- we want to be
     * sure ErrorContext still has some memory even if we've run out
     * elsewhere! Also, allow allocations in ErrorContext within a critical
     * section. Otherwise a PANIC will cause an assertion failure in the error
     * reporting code, before printing out the real cause of the failure.
     *
     * This should be the last step in this function, as elog.c assumes memory
     * management works once ErrorContext is non-null.
     */
    ErrorContext = AllocSetContextCreate(TopMemoryContext,
                                         "ErrorContext",
                                         8 * 1024,
                                         8 * 1024,
                                         8 * 1024);
    MemoryContextAllowInCriticalSection(ErrorContext, true);
}
 
/*
 * MemoryContextReset
 *      Release all space allocated within a context and delete all its
 *      descendant contexts (but not the named context itself).
 */
void
MemoryContextReset(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    /* save a function call in common case where there are no children */
    if (context->firstchild != NULL)
        MemoryContextDeleteChildren(context);
 
    /* save a function call if no pallocs since startup or last reset */
    if (!context->isReset)
        MemoryContextResetOnly(context);
}
 
/*
 * MemoryContextResetOnly
 *      Release all space allocated within a context.
 *      Nothing is done to the context's descendant contexts.
 */
void
MemoryContextResetOnly(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    /* Nothing to do if no pallocs since startup or last reset */
    if (!context->isReset)
    {
        MemoryContextCallResetCallbacks(context);
 
        /*
         * If context->ident points into the context's memory, it will become
         * a dangling pointer.  We could prevent that by setting it to NULL
         * here, but that would break valid coding patterns that keep the
         * ident elsewhere, e.g. in a parent context.  So for now we assume
         * the programmer got it right.
         */
 
        context->methods->reset(context);
        context->isReset = true;
    }
}
 
/*
 * MemoryContextResetChildren
 *      Release all space allocated within a context's descendants,
 *      but don't delete the contexts themselves.  The named context
 *      itself is not touched.
 */
void
MemoryContextResetChildren(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    for (MemoryContext curr = context->firstchild;
         curr != NULL;
         curr = MemoryContextTraverseNext(curr, context))
    {
        MemoryContextResetOnly(curr);
    }
}
 
/*
 * MemoryContextDelete
 *      Delete a context and its descendants, and release all space
 *      allocated therein.
 *
 * The type-specific delete routine removes all storage for the context,
 * but we have to deal with descendant nodes here.
 */
void
MemoryContextDelete(MemoryContext context)
{
    MemoryContext curr;
 
    Assert(MemoryContextIsValid(context));
 
    /*
     * Delete subcontexts from the bottom up.
     *
     * Note: Do not use recursion here.  A "stack depth limit exceeded" error
     * would be unpleasant if we're already in the process of cleaning up from
     * transaction abort.  We also cannot use MemoryContextTraverseNext() here
     * because we modify the tree as we go.
     */
    curr = context;
    for (;;)
    {
        MemoryContext parent;
 
        /* Descend down until we find a leaf context with no children */
        while (curr->firstchild != NULL)
            curr = curr->firstchild;
 
        /*
         * We're now at a leaf with no children. Free it and continue from the
         * parent.  Or if this was the original node, we're all done.
         */
        parent = curr->parent;
        MemoryContextDeleteOnly(curr);
 
        if (curr == context)
            break;
        curr = parent;
    }
}
 
/*
 * Subroutine of MemoryContextDelete,
 * to delete a context that has no children.
 * We must also delink the context from its parent, if it has one.
 */
static void
MemoryContextDeleteOnly(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
    /* We had better not be deleting TopMemoryContext ... */
    Assert(context != TopMemoryContext);
    /* And not CurrentMemoryContext, either */
    Assert(context != CurrentMemoryContext);
    /* All the children should've been deleted already */
    Assert(context->firstchild == NULL);
 
    /*
     * It's not entirely clear whether 'tis better to do this before or after
     * delinking the context; but an error in a callback will likely result in
     * leaking the whole context (if it's not a root context) if we do it
     * after, so let's do it before.
     */
    MemoryContextCallResetCallbacks(context);
 
    /*
     * We delink the context from its parent before deleting it, so that if
     * there's an error we won't have deleted/busted contexts still attached
     * to the context tree.  Better a leak than a crash.
     */
    MemoryContextSetParent(context, NULL);
 
    /*
     * Also reset the context's ident pointer, in case it points into the
     * context.  This would only matter if someone tries to get stats on the
     * (already unlinked) context, which is unlikely, but let's be safe.
     */
    context->ident = NULL;
 
    context->methods->delete_context(context);
}
 
/*
 * MemoryContextDeleteChildren
 *      Delete all the descendants of the named context and release all
 *      space allocated therein.  The named context itself is not touched.
 */
void
MemoryContextDeleteChildren(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    /*
     * MemoryContextDelete will delink the child from me, so just iterate as
     * long as there is a child.
     */
    while (context->firstchild != NULL)
        MemoryContextDelete(context->firstchild);
}
 
/*
 * MemoryContextRegisterResetCallback
 *      Register a function to be called before next context reset/delete.
 *      Such callbacks will be called in reverse order of registration.
 *
 * The caller is responsible for allocating a MemoryContextCallback struct
 * to hold the info about this callback request, and for filling in the
 * "func" and "arg" fields in the struct to show what function to call with
 * what argument.  Typically the callback struct should be allocated within
 * the specified context, since that means it will automatically be freed
 * when no longer needed.
 *
 * Note that callers can assume this cannot fail.
 */
void
MemoryContextRegisterResetCallback(MemoryContext context,
                                   MemoryContextCallback *cb)
{
    Assert(MemoryContextIsValid(context));
 
    /* Push onto head so this will be called before older registrants. */
    cb->next = context->reset_cbs;
    context->reset_cbs = cb;
    /* Mark the context as non-reset (it probably is already). */
    context->isReset = false;
}
 
/*
 * MemoryContextUnregisterResetCallback
 *      Undo the effects of MemoryContextRegisterResetCallback.
 *
 * This can be used if a callback's effects are no longer required
 * at some point before the context has been reset/deleted.  It is the
 * caller's responsibility to pfree the callback struct (if needed).
 *
 * An assertion failure occurs if the callback was not registered.
 * We could alternatively define that case as a no-op, but that seems too
 * likely to mask programming errors such as passing the wrong context.
 */
void
MemoryContextUnregisterResetCallback(MemoryContext context,
                                     MemoryContextCallback *cb)
{
    MemoryContextCallback *prev,
               *cur;
 
    Assert(MemoryContextIsValid(context));
 
    for (prev = NULL, cur = context->reset_cbs; cur != NULL;
         prev = cur, cur = cur->next)
    {
        if (cur != cb)
            continue;
        if (prev)
            prev->next = cur->next;
        else
            context->reset_cbs = cur->next;
        return;
    }
    Assert(false);
}
 
/*
 * MemoryContextCallResetCallbacks
 *      Internal function to call all registered callbacks for context.
 */
static void
MemoryContextCallResetCallbacks(MemoryContext context)
{
    MemoryContextCallback *cb;
 
    /*
     * We pop each callback from the list before calling.  That way, if an
     * error occurs inside the callback, we won't try to call it a second time
     * in the likely event that we reset or delete the context later.
     */
    while ((cb = context->reset_cbs) != NULL)
    {
        context->reset_cbs = cb->next;
        cb->func(cb->arg);
    }
}
 
/*
 * MemoryContextSetIdentifier
 *      Set the identifier string for a memory context.
 *
 * An identifier can be provided to help distinguish among different contexts
 * of the same kind in memory context stats dumps.  The identifier string
 * must live at least as long as the context it is for; typically it is
 * allocated inside that context, so that it automatically goes away on
 * context deletion.  Pass id = NULL to forget any old identifier.
 */
void
MemoryContextSetIdentifier(MemoryContext context, const char *id)
{
    Assert(MemoryContextIsValid(context));
    context->ident = id;
}
 
/*
 * MemoryContextSetParent
 *      Change a context to belong to a new parent (or no parent).
 *
 * We provide this as an API function because it is sometimes useful to
 * change a context's lifespan after creation.  For example, a context
 * might be created underneath a transient context, filled with data,
 * and then reparented underneath CacheMemoryContext to make it long-lived.
 * In this way no special effort is needed to get rid of the context in case
 * a failure occurs before its contents are completely set up.
 *
 * Callers often assume that this function cannot fail, so don't put any
 * elog(ERROR) calls in it.
 *
 * A possible caller error is to reparent a context under itself, creating
 * a loop in the context graph.  We assert here that context != new_parent,
 * but checking for multi-level loops seems more trouble than it's worth.
 */
void
MemoryContextSetParent(MemoryContext context, MemoryContext new_parent)
{
    Assert(MemoryContextIsValid(context));
    Assert(context != new_parent);
 
    /* Fast path if it's got correct parent already */
    if (new_parent == context->parent)
        return;
 
    /* Delink from existing parent, if any */
    if (context->parent)
    {
        MemoryContext parent = context->parent;
 
        if (context->prevchild != NULL)
            context->prevchild->nextchild = context->nextchild;
        else
        {
            Assert(parent->firstchild == context);
            parent->firstchild = context->nextchild;
        }
 
        if (context->nextchild != NULL)
            context->nextchild->prevchild = context->prevchild;
    }
 
    /* And relink */
    if (new_parent)
    {
        Assert(MemoryContextIsValid(new_parent));
        context->parent = new_parent;
        context->prevchild = NULL;
        context->nextchild = new_parent->firstchild;
        if (new_parent->firstchild != NULL)
            new_parent->firstchild->prevchild = context;
        new_parent->firstchild = context;
    }
    else
    {
        context->parent = NULL;
        context->prevchild = NULL;
        context->nextchild = NULL;
    }
}
 
/*
 * MemoryContextAllowInCriticalSection
 *      Allow/disallow allocations in this memory context within a critical
 *      section.
 *
 * Normally, memory allocations are not allowed within a critical section,
 * because a failure would lead to PANIC.  There are a few exceptions to
 * that, like allocations related to debugging code that is not supposed to
 * be enabled in production.  This function can be used to exempt specific
 * memory contexts from the assertion in palloc().
 */
void
MemoryContextAllowInCriticalSection(MemoryContext context, bool allow)
{
    Assert(MemoryContextIsValid(context));
 
    context->allowInCritSection = allow;
}
 
/*
 * GetMemoryChunkContext
 *      Given a currently-allocated chunk, determine the MemoryContext that
 *      the chunk belongs to.
 */
MemoryContext
GetMemoryChunkContext(void *pointer)
{
    return MCXT_METHOD(pointer, get_chunk_context) (pointer);
}
 
/*
 * GetMemoryChunkSpace
 *      Given a currently-allocated chunk, determine the total space
 *      it occupies (including all memory-allocation overhead).
 *
 * This is useful for measuring the total space occupied by a set of
 * allocated chunks.
 */
Size
GetMemoryChunkSpace(void *pointer)
{
    return MCXT_METHOD(pointer, get_chunk_space) (pointer);
}
 
/*
 * MemoryContextGetParent
 *      Get the parent context (if any) of the specified context
 */
MemoryContext
MemoryContextGetParent(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    return context->parent;
}
 
/*
 * MemoryContextIsEmpty
 *      Is a memory context empty of any allocated space?
 */
bool
MemoryContextIsEmpty(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
 
    /*
     * For now, we consider a memory context nonempty if it has any children;
     * perhaps this should be changed later.
     */
    if (context->firstchild != NULL)
        return false;
    /* Otherwise use the type-specific inquiry */
    return context->methods->is_empty(context);
}
 
/*
 * Find the memory allocated to blocks for this memory context. If recurse is
 * true, also include children.
 */
Size
MemoryContextMemAllocated(MemoryContext context, bool recurse)
{
    Size        total = context->mem_allocated;
 
    Assert(MemoryContextIsValid(context));
 
    if (recurse)
    {
        for (MemoryContext curr = context->firstchild;
             curr != NULL;
             curr = MemoryContextTraverseNext(curr, context))
        {
            total += curr->mem_allocated;
        }
    }
 
    return total;
}
 
/*
 * Return the memory consumption statistics about the given context and its
 * children.
 */
void
MemoryContextMemConsumed(MemoryContext context,
                         MemoryContextCounters *consumed)
{
    Assert(MemoryContextIsValid(context));
 
    memset(consumed, 0, sizeof(*consumed));
 
    /* Examine the context itself */
    context->methods->stats(context, NULL, NULL, consumed, false);
 
    /* Examine children, using iteration not recursion */
    for (MemoryContext curr = context->firstchild;
         curr != NULL;
         curr = MemoryContextTraverseNext(curr, context))
    {
        curr->methods->stats(curr, NULL, NULL, consumed, false);
    }
}
 
/*
 * MemoryContextStats
 *      Print statistics about the named context and all its descendants.
 *
 * This is just a debugging utility, so it's not very fancy.  However, we do
 * make some effort to summarize when the output would otherwise be very long.
 * The statistics are sent to stderr.
 */
void
MemoryContextStats(MemoryContext context)
{
    /* Hard-wired limits are usually good enough */
    MemoryContextStatsDetail(context, 100, 100, true);
}
 
/*
 * MemoryContextStatsDetail
 *
 * Entry point for use if you want to vary the number of child contexts shown.
 *
 * If print_to_stderr is true, print statistics about the memory contexts
 * with fprintf(stderr), otherwise use ereport().
 */
void
MemoryContextStatsDetail(MemoryContext context,
                         int max_level, int max_children,
                         bool print_to_stderr)
{
    MemoryContextCounters grand_totals;
 
    memset(&grand_totals, 0, sizeof(grand_totals));
 
    MemoryContextStatsInternal(context, 1, max_level, max_children,
                               &grand_totals, print_to_stderr);
 
    if (print_to_stderr)
        fprintf(stderr,
                "Grand total: %zu bytes in %zu blocks; %zu free (%zu chunks); %zu used\n",
                grand_totals.totalspace, grand_totals.nblocks,
                grand_totals.freespace, grand_totals.freechunks,
                grand_totals.totalspace - grand_totals.freespace);
    else
    {
        /*
         * Use LOG_SERVER_ONLY to prevent the memory contexts from being sent
         * to the connected client.
         *
         * We don't buffer the information about all memory contexts in a
         * backend into StringInfo and log it as one message.  That would
         * require the buffer to be enlarged, risking an OOM as there could be
         * a large number of memory contexts in a backend.  Instead, we log
         * one message per memory context.
         */
        ereport(LOG_SERVER_ONLY,
                (errhidestmt(true),
                 errhidecontext(true),
                 errmsg_internal("Grand total: %zu bytes in %zu blocks; %zu free (%zu chunks); %zu used",
                                 grand_totals.totalspace, grand_totals.nblocks,
                                 grand_totals.freespace, grand_totals.freechunks,
                                 grand_totals.totalspace - grand_totals.freespace)));
    }
}
 
/*
 * MemoryContextStatsInternal
 *      One recursion level for MemoryContextStats
 *
 * Print stats for this context if possible, but in any case accumulate counts
 * into *totals (if not NULL).
 */
static void
MemoryContextStatsInternal(MemoryContext context, int level,
                           int max_level, int max_children,
                           MemoryContextCounters *totals,
                           bool print_to_stderr)
{
    MemoryContext child;
    int         ichild;
 
    Assert(MemoryContextIsValid(context));
 
    /* Examine the context itself */
    context->methods->stats(context,
                            MemoryContextStatsPrint,
                            &level,
                            totals, print_to_stderr);
 
    /*
     * Examine children.
     *
     * If we are past the recursion depth limit or already running low on
     * stack, do not print them explicitly but just summarize them. Similarly,
     * if there are more than max_children of them, we do not print the rest
     * explicitly, but just summarize them.
     */
    child = context->firstchild;
    ichild = 0;
    if (level <= max_level && !stack_is_too_deep())
    {
        for (; child != NULL && ichild < max_children;
             child = child->nextchild, ichild++)
        {
            MemoryContextStatsInternal(child, level + 1,
                                       max_level, max_children,
                                       totals,
                                       print_to_stderr);
        }
    }
 
    if (child != NULL)
    {
        /* Summarize the rest of the children, avoiding recursion. */
        MemoryContextCounters local_totals;
 
        memset(&local_totals, 0, sizeof(local_totals));
 
        ichild = 0;
        while (child != NULL)
        {
            child->methods->stats(child, NULL, NULL, &local_totals, false);
            ichild++;
            child = MemoryContextTraverseNext(child, context);
        }
 
        if (print_to_stderr)
        {
            for (int i = 0; i < level; i++)
                fprintf(stderr, "  ");
            fprintf(stderr,
                    "%d more child contexts containing %zu total in %zu blocks; %zu free (%zu chunks); %zu used\n",
                    ichild,
                    local_totals.totalspace,
                    local_totals.nblocks,
                    local_totals.freespace,
                    local_totals.freechunks,
                    local_totals.totalspace - local_totals.freespace);
        }
        else
            ereport(LOG_SERVER_ONLY,
                    (errhidestmt(true),
                     errhidecontext(true),
                     errmsg_internal("level: %d; %d more child contexts containing %zu total in %zu blocks; %zu free (%zu chunks); %zu used",
                                     level,
                                     ichild,
                                     local_totals.totalspace,
                                     local_totals.nblocks,
                                     local_totals.freespace,
                                     local_totals.freechunks,
                                     local_totals.totalspace - local_totals.freespace)));
 
        if (totals)
        {
            totals->nblocks += local_totals.nblocks;
            totals->freechunks += local_totals.freechunks;
            totals->totalspace += local_totals.totalspace;
            totals->freespace += local_totals.freespace;
        }
    }
}
 
/*
 * MemoryContextStatsPrint
 *      Print callback used by MemoryContextStatsInternal
 *
 * For now, the passthru pointer just points to "int level"; later we might
 * make that more complicated.
 */
static void
MemoryContextStatsPrint(MemoryContext context, void *passthru,
                        const char *stats_string,
                        bool print_to_stderr)
{
    int         level = *(int *) passthru;
    const char *name = context->name;
    const char *ident = context->ident;
    char        truncated_ident[110];
    int         i;
 
    /*
     * It seems preferable to label dynahash contexts with just the hash table
     * name.  Those are already unique enough, so the "dynahash" part isn't
     * very helpful, and this way is more consistent with pre-v11 practice.
     */
    if (ident && strcmp(name, "dynahash") == 0)
    {
        name = ident;
        ident = NULL;
    }
 
    truncated_ident[0] = '\0';
 
    if (ident)
    {
        /*
         * Some contexts may have very long identifiers (e.g., SQL queries).
         * Arbitrarily truncate at 100 bytes, but be careful not to break
         * multibyte characters.  Also, replace ASCII control characters, such
         * as newlines, with spaces.
         */
        int         idlen = strlen(ident);
        bool        truncated = false;
 
        strcpy(truncated_ident, ": ");
        i = strlen(truncated_ident);
 
        if (idlen > 100)
        {
            idlen = pg_mbcliplen(ident, idlen, 100);
            truncated = true;
        }
 
        while (idlen-- > 0)
        {
            unsigned char c = *ident++;
 
            if (c < ' ')
                c = ' ';
            truncated_ident[i++] = c;
        }
        truncated_ident[i] = '\0';
 
        if (truncated)
            strcat(truncated_ident, "...");
    }
 
    if (print_to_stderr)
    {
        for (i = 1; i < level; i++)
            fprintf(stderr, "  ");
        fprintf(stderr, "%s: %s%s\n", name, stats_string, truncated_ident);
    }
    else
        ereport(LOG_SERVER_ONLY,
                (errhidestmt(true),
                 errhidecontext(true),
                 errmsg_internal("level: %d; %s: %s%s",
                                 level, name, stats_string, truncated_ident)));
}
 
/*
 * MemoryContextCheck
 *      Check all chunks in the named context and its children.
 *
 * This is just a debugging utility, so it's not fancy.
 */
#ifdef MEMORY_CONTEXT_CHECKING
void
MemoryContextCheck(MemoryContext context)
{
    Assert(MemoryContextIsValid(context));
    context->methods->check(context);
 
    for (MemoryContext curr = context->firstchild;
         curr != NULL;
         curr = MemoryContextTraverseNext(curr, context))
    {
        Assert(MemoryContextIsValid(curr));
        curr->methods->check(curr);
    }
}
#endif
 
/*
 * MemoryContextCreate
 *      Context-type-independent part of context creation.
 *
 * This is only intended to be called by context-type-specific
 * context creation routines, not by the unwashed masses.
 *
 * The memory context creation procedure goes like this:
 *  1.  Context-type-specific routine makes some initial space allocation,
 *      including enough space for the context header.  If it fails,
 *      it can ereport() with no damage done.
 *  2.  Context-type-specific routine sets up all type-specific fields of
 *      the header (those beyond MemoryContextData proper), as well as any
 *      other management fields it needs to have a fully valid context.
 *      Usually, failure in this step is impossible, but if it's possible
 *      the initial space allocation should be freed before ereport'ing.
 *  3.  Context-type-specific routine calls MemoryContextCreate() to fill in
 *      the generic header fields and link the context into the context tree.
 *  4.  We return to the context-type-specific routine, which finishes
 *      up type-specific initialization.  This routine can now do things
 *      that might fail (like allocate more memory), so long as it's
 *      sure the node is left in a state that delete will handle.
 *
 * node: the as-yet-uninitialized common part of the context header node.
 * tag: NodeTag code identifying the memory context type.
 * method_id: MemoryContextMethodID of the context-type being created.
 * parent: parent context, or NULL if this will be a top-level context.
 * name: name of context (must be statically allocated).
 *
 * Context routines generally assume that MemoryContextCreate can't fail,
 * so this can contain Assert but not elog/ereport.
 */
void
MemoryContextCreate(MemoryContext node,
                    NodeTag tag,
                    MemoryContextMethodID method_id,
                    MemoryContext parent,
                    const char *name)
{
    /* Creating new memory contexts is not allowed in a critical section */
    Assert(CritSectionCount == 0);
 
    /* Validate parent, to help prevent crazy context linkages */
    Assert(parent == NULL || MemoryContextIsValid(parent));
    Assert(node != parent);
 
    /* Initialize all standard fields of memory context header */
    node->type = tag;
    node->isReset = true;
    node->methods = &mcxt_methods[method_id];
    node->parent = parent;
    node->firstchild = NULL;
    node->mem_allocated = 0;
    node->prevchild = NULL;
    node->name = name;
    node->ident = NULL;
    node->reset_cbs = NULL;
 
    /* OK to link node into context tree */
    if (parent)
    {
        node->nextchild = parent->firstchild;
        if (parent->firstchild != NULL)
            parent->firstchild->prevchild = node;
        parent->firstchild = node;
        /* inherit allowInCritSection flag from parent */
        node->allowInCritSection = parent->allowInCritSection;
    }
    else
    {
        node->nextchild = NULL;
        node->allowInCritSection = false;
    }
}
 
/*
 * MemoryContextAllocationFailure
 *      For use by MemoryContextMethods implementations to handle when malloc
 *      returns NULL.  The behavior is specific to whether MCXT_ALLOC_NO_OOM
 *      is in 'flags'.
 */
void *
MemoryContextAllocationFailure(MemoryContext context, Size size, int flags)
{
    if ((flags & MCXT_ALLOC_NO_OOM) == 0)
    {
        if (TopMemoryContext)
            MemoryContextStats(TopMemoryContext);
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("out of memory"),
                 errdetail("Failed on request of size %zu in memory context \"%s\".",
                           size, context->name)));
    }
    return NULL;
}
 
/*
 * MemoryContextSizeFailure
 *      For use by MemoryContextMethods implementations to handle invalid
 *      memory allocation request sizes.
 */
void
MemoryContextSizeFailure(MemoryContext context, Size size, int flags)
{
    elog(ERROR, "invalid memory alloc request size %zu", size);
}
 
/*
 * MemoryContextAlloc
 *      Allocate space within the specified context.
 *
 * This could be turned into a macro, but we'd have to import
 * nodes/memnodes.h into postgres.h which seems a bad idea.
 */
void *
MemoryContextAlloc(MemoryContext context, Size size)
{
    void       *ret;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    /*
     * For efficiency reasons, we purposefully offload the handling of
     * allocation failures to the MemoryContextMethods implementation as this
     * allows these checks to be performed only when an actual malloc needs to
     * be done to request more memory from the OS.  Additionally, not having
     * to execute any instructions after this call allows the compiler to use
     * the sibling call optimization.  If you're considering adding code after
     * this call, consider making it the responsibility of the 'alloc'
     * function instead.
     */
    ret = context->methods->alloc(context, size, 0);
 
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    return ret;
}
 
/*
 * MemoryContextAllocZero
 *      Like MemoryContextAlloc, but clears allocated memory
 *
 *  We could just call MemoryContextAlloc then clear the memory, but this
 *  is a very common combination, so we provide the combined operation.
 */
void *
MemoryContextAllocZero(MemoryContext context, Size size)
{
    void       *ret;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    ret = context->methods->alloc(context, size, 0);
 
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    MemSetAligned(ret, 0, size);
 
    return ret;
}
 
/*
 * MemoryContextAllocExtended
 *      Allocate space within the specified context using the given flags.
 */
void *
MemoryContextAllocExtended(MemoryContext context, Size size, int flags)
{
    void       *ret;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    if (!((flags & MCXT_ALLOC_HUGE) != 0 ? AllocHugeSizeIsValid(size) :
          AllocSizeIsValid(size)))
        elog(ERROR, "invalid memory alloc request size %zu", size);
 
    context->isReset = false;
 
    ret = context->methods->alloc(context, size, flags);
    if (unlikely(ret == NULL))
        return NULL;
 
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    if ((flags & MCXT_ALLOC_ZERO) != 0)
        MemSetAligned(ret, 0, size);
 
    return ret;
}
 
/*
 * HandleLogMemoryContextInterrupt
 *      Handle receipt of an interrupt indicating logging of memory
 *      contexts.
 *
 * All the actual work is deferred to ProcessLogMemoryContextInterrupt(),
 * because we cannot safely emit a log message inside the signal handler.
 */
void
HandleLogMemoryContextInterrupt(void)
{
    InterruptPending = true;
    LogMemoryContextPending = true;
    /* latch will be set by procsignal_sigusr1_handler */
}
 
/*
 * ProcessLogMemoryContextInterrupt
 *      Perform logging of memory contexts of this backend process.
 *
 * Any backend that participates in ProcSignal signaling must arrange
 * to call this function if we see LogMemoryContextPending set.
 * It is called from CHECK_FOR_INTERRUPTS(), which is enough because
 * the target process for logging of memory contexts is a backend.
 */
void
ProcessLogMemoryContextInterrupt(void)
{
    LogMemoryContextPending = false;
 
    /*
     * Exit immediately if memory context logging is already in progress. This
     * prevents recursive calls, which could occur if logging is requested
     * repeatedly and rapidly, potentially leading to infinite recursion and a
     * crash.
     */
    if (LogMemoryContextInProgress)
        return;
    LogMemoryContextInProgress = true;
 
    PG_TRY();
    {
        /*
         * Use LOG_SERVER_ONLY to prevent this message from being sent to the
         * connected client.
         */
        ereport(LOG_SERVER_ONLY,
                (errhidestmt(true),
                 errhidecontext(true),
                 errmsg("logging memory contexts of PID %d", MyProcPid)));
 
        /*
         * When a backend process is consuming huge memory, logging all its
         * memory contexts might overrun available disk space. To prevent
         * this, we limit the depth of the hierarchy, as well as the number of
         * child contexts to log per parent to 100.
         *
         * As with MemoryContextStats(), we suppose that practical cases where
         * the dump gets long will typically be huge numbers of siblings under
         * the same parent context; while the additional debugging value from
         * seeing details about individual siblings beyond 100 will not be
         * large.
         */
        MemoryContextStatsDetail(TopMemoryContext, 100, 100, false);
    }
    PG_FINALLY();
    {
        LogMemoryContextInProgress = false;
    }
    PG_END_TRY();
}
 
void *
palloc(Size size)
{
    /* duplicates MemoryContextAlloc to avoid increased overhead */
    void       *ret;
    MemoryContext context = CurrentMemoryContext;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    /*
     * For efficiency reasons, we purposefully offload the handling of
     * allocation failures to the MemoryContextMethods implementation as this
     * allows these checks to be performed only when an actual malloc needs to
     * be done to request more memory from the OS.  Additionally, not having
     * to execute any instructions after this call allows the compiler to use
     * the sibling call optimization.  If you're considering adding code after
     * this call, consider making it the responsibility of the 'alloc'
     * function instead.
     */
    ret = context->methods->alloc(context, size, 0);
    /* We expect OOM to be handled by the alloc function */
    Assert(ret != NULL);
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    return ret;
}
 
void *
palloc0(Size size)
{
    /* duplicates MemoryContextAllocZero to avoid increased overhead */
    void       *ret;
    MemoryContext context = CurrentMemoryContext;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    ret = context->methods->alloc(context, size, 0);
    /* We expect OOM to be handled by the alloc function */
    Assert(ret != NULL);
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    MemSetAligned(ret, 0, size);
 
    return ret;
}
 
void *
palloc_extended(Size size, int flags)
{
    /* duplicates MemoryContextAllocExtended to avoid increased overhead */
    void       *ret;
    MemoryContext context = CurrentMemoryContext;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    ret = context->methods->alloc(context, size, flags);
    if (unlikely(ret == NULL))
    {
        /* NULL can be returned only when using MCXT_ALLOC_NO_OOM */
        Assert(flags & MCXT_ALLOC_NO_OOM);
        return NULL;
    }
 
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    if ((flags & MCXT_ALLOC_ZERO) != 0)
        MemSetAligned(ret, 0, size);
 
    return ret;
}
 
/*
 * MemoryContextAllocAligned
 *      Allocate 'size' bytes of memory in 'context' aligned to 'alignto'
 *      bytes.
 *
 * Currently, we align addresses by requesting additional bytes from the
 * MemoryContext's standard allocator function and then aligning the returned
 * address by the required alignment.  This means that the given MemoryContext
 * must support providing us with a chunk of memory that's larger than 'size'.
 * For allocators such as Slab, that's not going to work, as slab only allows
 * chunks of the size that's specified when the context is created.
 *
 * 'alignto' must be a power of 2.
 * 'flags' may be 0 or set the same as MemoryContextAllocExtended().
 */
void *
MemoryContextAllocAligned(MemoryContext context,
                          Size size, Size alignto, int flags)
{
    MemoryChunk *alignedchunk;
    Size        alloc_size;
    void       *unaligned;
    void       *aligned;
 
    /*
     * Restrict alignto to ensure that it can fit into the "value" field of
     * the redirection MemoryChunk, and that the distance back to the start of
     * the unaligned chunk will fit into the space available for that.  This
     * isn't a limitation in practice, since it wouldn't make much sense to
     * waste that much space.
     */
    Assert(alignto < (128 * 1024 * 1024));
 
    /* ensure alignto is a power of 2 */
    Assert((alignto & (alignto - 1)) == 0);
 
    /*
     * If the alignment requirements are less than what we already guarantee
     * then just use the standard allocation function.
     */
    if (unlikely(alignto <= MAXIMUM_ALIGNOF))
        return MemoryContextAllocExtended(context, size, flags);
 
    /*
     * We implement aligned pointers by simply allocating enough memory for
     * the requested size plus the alignment and an additional "redirection"
     * MemoryChunk.  This additional MemoryChunk is required for operations
     * such as pfree when used on the pointer returned by this function.  We
     * use this redirection MemoryChunk in order to find the pointer to the
     * memory that was returned by the MemoryContextAllocExtended call below.
     * We do that by "borrowing" the block offset field and instead of using
     * that to find the offset into the owning block, we use it to find the
     * original allocated address.
     *
     * Here we must allocate enough extra memory so that we can still align
     * the pointer returned by MemoryContextAllocExtended and also have enough
     * space for the redirection MemoryChunk.  Since allocations will already
     * be at least aligned by MAXIMUM_ALIGNOF, we can subtract that amount
     * from the allocation size to save a little memory.
     */
    alloc_size = size + PallocAlignedExtraBytes(alignto);
 
#ifdef MEMORY_CONTEXT_CHECKING
    /* ensure there's space for a sentinel byte */
    alloc_size += 1;
#endif
 
    /*
     * Perform the actual allocation, but do not pass down MCXT_ALLOC_ZERO.
     * This ensures that wasted bytes beyond the aligned chunk do not become
     * DEFINED.
     */
    unaligned = MemoryContextAllocExtended(context, alloc_size,
                                           flags & ~MCXT_ALLOC_ZERO);
 
    /* compute the aligned pointer */
    aligned = (void *) TYPEALIGN(alignto, (char *) unaligned +
                                 sizeof(MemoryChunk));
 
    alignedchunk = PointerGetMemoryChunk(aligned);
 
    /*
     * We set the redirect MemoryChunk so that the block offset calculation is
     * used to point back to the 'unaligned' allocated chunk.  This allows us
     * to use MemoryChunkGetBlock() to find the unaligned chunk when we need
     * to perform operations such as pfree() and repalloc().
     *
     * We store 'alignto' in the MemoryChunk's 'value' so that we know what
     * the alignment was set to should we ever be asked to realloc this
     * pointer.
     */
    MemoryChunkSetHdrMask(alignedchunk, unaligned, alignto,
                          MCTX_ALIGNED_REDIRECT_ID);
 
    /* double check we produced a correctly aligned pointer */
    Assert((void *) TYPEALIGN(alignto, aligned) == aligned);
 
#ifdef MEMORY_CONTEXT_CHECKING
    alignedchunk->requested_size = size;
    /* set mark to catch clobber of "unused" space */
    set_sentinel(aligned, size);
#endif
 
    /*
     * MemoryContextAllocExtended marked the whole unaligned chunk as a
     * vchunk.  Undo that, instead making just the aligned chunk be a vchunk.
     * This prevents Valgrind from complaining that the vchunk is possibly
     * leaked, since only pointers to the aligned chunk will exist.
     *
     * After these calls, the aligned chunk will be marked UNDEFINED, and all
     * the rest of the unaligned chunk (the redirection chunk header, the
     * padding bytes before it, and any wasted trailing bytes) will be marked
     * NOACCESS, which is what we want.
     */
    VALGRIND_MEMPOOL_FREE(context, unaligned);
    VALGRIND_MEMPOOL_ALLOC(context, aligned, size);
 
    /* Now zero (and make DEFINED) just the aligned chunk, if requested */
    if ((flags & MCXT_ALLOC_ZERO) != 0)
        MemSetAligned(aligned, 0, size);
 
    return aligned;
}
 
/*
 * palloc_aligned
 *      Allocate 'size' bytes returning a pointer that's aligned to the
 *      'alignto' boundary.
 *
 * Currently, we align addresses by requesting additional bytes from the
 * MemoryContext's standard allocator function and then aligning the returned
 * address by the required alignment.  This means that the given MemoryContext
 * must support providing us with a chunk of memory that's larger than 'size'.
 * For allocators such as Slab, that's not going to work, as slab only allows
 * chunks of the size that's specified when the context is created.
 *
 * 'alignto' must be a power of 2.
 * 'flags' may be 0 or set the same as MemoryContextAllocExtended().
 */
void *
palloc_aligned(Size size, Size alignto, int flags)
{
    return MemoryContextAllocAligned(CurrentMemoryContext, size, alignto, flags);
}
 
/*
 * pfree
 *      Release an allocated chunk.
 */
void
pfree(void *pointer)
{
#ifdef USE_VALGRIND
    MemoryContext context = GetMemoryChunkContext(pointer);
#endif
 
    MCXT_METHOD(pointer, free_p) (pointer);
 
    VALGRIND_MEMPOOL_FREE(context, pointer);
}
 
/*
 * repalloc
 *      Adjust the size of a previously allocated chunk.
 */
void *
repalloc(void *pointer, Size size)
{
#if defined(USE_ASSERT_CHECKING) || defined(USE_VALGRIND)
    MemoryContext context = GetMemoryChunkContext(pointer);
#endif
    void       *ret;
 
    AssertNotInCriticalSection(context);
 
    /* isReset must be false already */
    Assert(!context->isReset);
 
    /*
     * For efficiency reasons, we purposefully offload the handling of
     * allocation failures to the MemoryContextMethods implementation as this
     * allows these checks to be performed only when an actual malloc needs to
     * be done to request more memory from the OS.  Additionally, not having
     * to execute any instructions after this call allows the compiler to use
     * the sibling call optimization.  If you're considering adding code after
     * this call, consider making it the responsibility of the 'realloc'
     * function instead.
     */
    ret = MCXT_METHOD(pointer, realloc) (pointer, size, 0);
 
    VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);
 
    return ret;
}
 
/*
 * repalloc_extended
 *      Adjust the size of a previously allocated chunk,
 *      with HUGE and NO_OOM options.
 */
void *
repalloc_extended(void *pointer, Size size, int flags)
{
#if defined(USE_ASSERT_CHECKING) || defined(USE_VALGRIND)
    MemoryContext context = GetMemoryChunkContext(pointer);
#endif
    void       *ret;
 
    AssertNotInCriticalSection(context);
 
    /* isReset must be false already */
    Assert(!context->isReset);
 
    /*
     * For efficiency reasons, we purposefully offload the handling of
     * allocation failures to the MemoryContextMethods implementation as this
     * allows these checks to be performed only when an actual malloc needs to
     * be done to request more memory from the OS.  Additionally, not having
     * to execute any instructions after this call allows the compiler to use
     * the sibling call optimization.  If you're considering adding code after
     * this call, consider making it the responsibility of the 'realloc'
     * function instead.
     */
    ret = MCXT_METHOD(pointer, realloc) (pointer, size, flags);
    if (unlikely(ret == NULL))
        return NULL;
 
    VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);
 
    return ret;
}
 
/*
 * repalloc0
 *      Adjust the size of a previously allocated chunk and zero out the added
 *      space.
 */
void *
repalloc0(void *pointer, Size oldsize, Size size)
{
    void       *ret;
 
    /* catch wrong argument order */
    if (unlikely(oldsize > size))
        elog(ERROR, "invalid repalloc0 call: oldsize %zu, new size %zu",
             oldsize, size);
 
    ret = repalloc(pointer, size);
    memset((char *) ret + oldsize, 0, (size - oldsize));
    return ret;
}
 
/*
 * MemoryContextAllocHuge
 *      Allocate (possibly-expansive) space within the specified context.
 *
 * See considerations in comment at MaxAllocHugeSize.
 */
void *
MemoryContextAllocHuge(MemoryContext context, Size size)
{
    void       *ret;
 
    Assert(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);
 
    context->isReset = false;
 
    /*
     * For efficiency reasons, we purposefully offload the handling of
     * allocation failures to the MemoryContextMethods implementation as this
     * allows these checks to be performed only when an actual malloc needs to
     * be done to request more memory from the OS.  Additionally, not having
     * to execute any instructions after this call allows the compiler to use
     * the sibling call optimization.  If you're considering adding code after
     * this call, consider making it the responsibility of the 'alloc'
     * function instead.
     */
    ret = context->methods->alloc(context, size, MCXT_ALLOC_HUGE);
 
    VALGRIND_MEMPOOL_ALLOC(context, ret, size);
 
    return ret;
}
 
/*
 * repalloc_huge
 *      Adjust the size of a previously allocated chunk, permitting a large
 *      value.  The previous allocation need not have been "huge".
 */
void *
repalloc_huge(void *pointer, Size size)
{
    /* this one seems not worth its own implementation */
    return repalloc_extended(pointer, size, MCXT_ALLOC_HUGE);
}
 
/*
 * MemoryContextStrdup
 *      Like strdup(), but allocate from the specified context
 */
char *
MemoryContextStrdup(MemoryContext context, const char *string)
{
    char       *nstr;
    Size        len = strlen(string) + 1;
 
    nstr = (char *) MemoryContextAlloc(context, len);
 
    memcpy(nstr, string, len);
 
    return nstr;
}
 
char *
pstrdup(const char *in)
{
    return MemoryContextStrdup(CurrentMemoryContext, in);
}
 
/*
 * pnstrdup
 *      Like pstrdup(), but append null byte to a
 *      not-necessarily-null-terminated input string.
 */
char *
pnstrdup(const char *in, Size len)
{
    char       *out;
 
    len = strnlen(in, len);
 
    out = palloc(len + 1);
    memcpy(out, in, len);
    out[len] = '\0';
 
    return out;
}
 
/*
 * Make copy of string with all trailing newline characters removed.
 */
char *
pchomp(const char *in)
{
    size_t      n;
 
    n = strlen(in);
    while (n > 0 && in[n - 1] == '\n')
        n--;
    return pnstrdup(in, n);
}