mcxt.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * 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.
 *
 *
 * Portions Copyright (c) 1996-2021, 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 "storage/proc.h"
#include "storage/procarray.h"
#include "storage/procsignal.h"
#include "utils/fmgrprotos.h"
#include "utils/memdebug.h"
#include "utils/memutils.h"


/*****************************************************************************
 *    GLOBAL MEMORY                                                          *
 *****************************************************************************/

/*
 * 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;

static void MemoryContextCallResetCallbacks(MemoryContext context);
static void MemoryContextStatsInternal(MemoryContext context, int level,
                                       bool print, 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)


/*****************************************************************************
 *    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)
{
    AssertState(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)
{
    AssertArg(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)
{
    AssertArg(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.  Another idea is to use
         * MemoryContextContains(), but we don't require ident strings to be
         * in separately-palloc'd chunks, so that risks false positives.  So
         * for now we assume the programmer got it right.
         */

        context->methods->reset(context);
        context->isReset = true;
        VALGRIND_DESTROY_MEMPOOL(context);
        VALGRIND_CREATE_MEMPOOL(context, 0, false);
    }
}

/*
 * 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)
{
    MemoryContext child;

    AssertArg(MemoryContextIsValid(context));

    for (child = context->firstchild; child != NULL; child = child->nextchild)
    {
        MemoryContextResetChildren(child);
        MemoryContextResetOnly(child);
    }
}

/*
 * 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 recurse to handle the children.
 * We must also delink the context from its parent, if it has one.
 */
void
MemoryContextDelete(MemoryContext context)
{
    AssertArg(MemoryContextIsValid(context));
    /* We had better not be deleting TopMemoryContext ... */
    Assert(context != TopMemoryContext);
    /* And not CurrentMemoryContext, either */
    Assert(context != CurrentMemoryContext);

    /* save a function call in common case where there are no children */
    if (context->firstchild != NULL)
        MemoryContextDeleteChildren(context);

    /*
     * 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);

    VALGRIND_DESTROY_MEMPOOL(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)
{
    AssertArg(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.
 *
 * There is no API for deregistering a callback once registered.  If you
 * want it to not do anything anymore, adjust the state pointed to by its
 * "arg" to indicate that.
 */
void
MemoryContextRegisterResetCallback(MemoryContext context,
                                   MemoryContextCallback *cb)
{
    AssertArg(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;
}

/*
 * 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)
{
    AssertArg(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)
{
    AssertArg(MemoryContextIsValid(context));
    AssertArg(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)
    {
        AssertArg(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)
{
    AssertArg(MemoryContextIsValid(context));

    context->allowInCritSection = allow;
}

/*
 * 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)
{
    MemoryContext context = GetMemoryChunkContext(pointer);

    return context->methods->get_chunk_space(context, pointer);
}

/*
 * MemoryContextGetParent
 *      Get the parent context (if any) of the specified context
 */
MemoryContext
MemoryContextGetParent(MemoryContext context)
{
    AssertArg(MemoryContextIsValid(context));

    return context->parent;
}

/*
 * MemoryContextIsEmpty
 *      Is a memory context empty of any allocated space?
 */
bool
MemoryContextIsEmpty(MemoryContext context)
{
    AssertArg(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;

    AssertArg(MemoryContextIsValid(context));

    if (recurse)
    {
        MemoryContext child;

        for (child = context->firstchild;
             child != NULL;
             child = child->nextchild)
            total += MemoryContextMemAllocated(child, true);
    }

    return total;
}

/*
 * 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)
{
    /* A hard-wired limit on the number of children is usually good enough */
    MemoryContextStatsDetail(context, 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_children,
                         bool print_to_stderr)
{
    MemoryContextCounters grand_totals;

    memset(&grand_totals, 0, sizeof(grand_totals));

    MemoryContextStatsInternal(context, 0, true, max_children, &grand_totals, print_to_stderr);

    if (print_to_stderr)
        fprintf(stderr,
                "Grand total: %zu bytes in %zd blocks; %zu free (%zd 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. Otherwise which
         * may require the buffer to be enlarged very much and lead to OOM
         * error since there can 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 %zd blocks; %zu free (%zd 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 this context if print is true, but in any case accumulate counts into
 * *totals (if given).
 */
static void
MemoryContextStatsInternal(MemoryContext context, int level,
                           bool print, int max_children,
                           MemoryContextCounters *totals,
                           bool print_to_stderr)
{
    MemoryContextCounters local_totals;
    MemoryContext child;
    int         ichild;

    AssertArg(MemoryContextIsValid(context));

    /* Examine the context itself */
    context->methods->stats(context,
                            print ? MemoryContextStatsPrint : NULL,
                            (void *) &level,
                            totals, print_to_stderr);

    /*
     * Examine children.  If there are more than max_children of them, we do
     * not print the rest explicitly, but just summarize them.
     */
    memset(&local_totals, 0, sizeof(local_totals));

    for (child = context->firstchild, ichild = 0;
         child != NULL;
         child = child->nextchild, ichild++)
    {
        if (ichild < max_children)
            MemoryContextStatsInternal(child, level + 1,
                                       print, max_children,
                                       totals,
                                       print_to_stderr);
        else
            MemoryContextStatsInternal(child, level + 1,
                                       false, max_children,
                                       &local_totals,
                                       print_to_stderr);
    }

    /* Deal with excess children */
    if (ichild > max_children)
    {
        if (print)
        {
            if (print_to_stderr)
            {
                int         i;

                for (i = 0; i <= level; i++)
                    fprintf(stderr, "  ");
                fprintf(stderr,
                        "%d more child contexts containing %zu total in %zd blocks; %zu free (%zd chunks); %zu used\n",
                        ichild - max_children,
                        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 %zd blocks; %zu free (%zd chunks); %zu used",
                                         level,
                                         ichild - max_children,
                                         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 = 0; 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.
 *
 * This is just a debugging utility, so it's not fancy.
 */
#ifdef MEMORY_CONTEXT_CHECKING
void
MemoryContextCheck(MemoryContext context)
{
    MemoryContext child;

    AssertArg(MemoryContextIsValid(context));

    context->methods->check(context);
    for (child = context->firstchild; child != NULL; child = child->nextchild)
        MemoryContextCheck(child);
}
#endif

/*
 * MemoryContextContains
 *      Detect whether an allocated chunk of memory belongs to a given
 *      context or not.
 *
 * Caution: this test is reliable as long as 'pointer' does point to
 * a chunk of memory allocated from *some* context.  If 'pointer' points
 * at memory obtained in some other way, there is a small chance of a
 * false-positive result, since the bits right before it might look like
 * a valid chunk header by chance.
 */
bool
MemoryContextContains(MemoryContext context, void *pointer)
{
    MemoryContext ptr_context;

    /*
     * NB: Can't use GetMemoryChunkContext() here - that performs assertions
     * that aren't acceptable here since we might be passed memory not
     * allocated by any memory context.
     *
     * 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.
     */
    if (pointer == NULL || pointer != (void *) MAXALIGN(pointer))
        return false;

    /*
     * OK, it's probably safe to look at the context.
     */
    ptr_context = *(MemoryContext *) (((char *) pointer) - sizeof(void *));

    return ptr_context == context;
}

/*
 * 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.
 * methods: context-type-specific methods (usually statically allocated).
 * 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,
                    const MemoryContextMethods *methods,
                    MemoryContext parent,
                    const char *name)
{
    /* Creating new memory contexts is not allowed in a critical section */
    Assert(CritSectionCount == 0);

    /* Initialize all standard fields of memory context header */
    node->type = tag;
    node->isReset = true;
    node->methods = methods;
    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;
    }

    VALGRIND_CREATE_MEMPOOL(node, 0, false);
}

/*
 * 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;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        MemoryContextStats(TopMemoryContext);

        /*
         * Here, and elsewhere in this module, we show the target context's
         * "name" but not its "ident" (if any) in user-visible error messages.
         * The "ident" string might contain security-sensitive data, such as
         * values in SQL commands.
         */
        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)));
    }

    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;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    VALGRIND_MEMPOOL_ALLOC(context, ret, size);

    MemSetAligned(ret, 0, size);

    return ret;
}

/*
 * MemoryContextAllocZeroAligned
 *      MemoryContextAllocZero where length is suitable for MemSetLoop
 *
 *  This might seem overly specialized, but it's not because newNode()
 *  is so often called with compile-time-constant sizes.
 */
void *
MemoryContextAllocZeroAligned(MemoryContext context, Size size)
{
    void       *ret;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    VALGRIND_MEMPOOL_ALLOC(context, ret, size);

    MemSetLoop(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;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (((flags & MCXT_ALLOC_HUGE) != 0 && !AllocHugeSizeIsValid(size)) ||
        ((flags & MCXT_ALLOC_HUGE) == 0 && !AllocSizeIsValid(size)))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        if ((flags & MCXT_ALLOC_NO_OOM) == 0)
        {
            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;
    }

    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;

    ereport(LOG,
            (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 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, false);
}

void *
palloc(Size size)
{
    /* duplicates MemoryContextAlloc to avoid increased overhead */
    void       *ret;
    MemoryContext context = CurrentMemoryContext;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    VALGRIND_MEMPOOL_ALLOC(context, ret, size);

    return ret;
}

void *
palloc0(Size size)
{
    /* duplicates MemoryContextAllocZero to avoid increased overhead */
    void       *ret;
    MemoryContext context = CurrentMemoryContext;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    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;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (((flags & MCXT_ALLOC_HUGE) != 0 && !AllocHugeSizeIsValid(size)) ||
        ((flags & MCXT_ALLOC_HUGE) == 0 && !AllocSizeIsValid(size)))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        if ((flags & MCXT_ALLOC_NO_OOM) == 0)
        {
            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;
    }

    VALGRIND_MEMPOOL_ALLOC(context, ret, size);

    if ((flags & MCXT_ALLOC_ZERO) != 0)
        MemSetAligned(ret, 0, size);

    return ret;
}

/*
 * pfree
 *      Release an allocated chunk.
 */
void
pfree(void *pointer)
{
    MemoryContext context = GetMemoryChunkContext(pointer);

    context->methods->free_p(context, pointer);
    VALGRIND_MEMPOOL_FREE(context, pointer);
}

/*
 * repalloc
 *      Adjust the size of a previously allocated chunk.
 */
void *
repalloc(void *pointer, Size size)
{
    MemoryContext context = GetMemoryChunkContext(pointer);
    void       *ret;

    if (!AllocSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    AssertNotInCriticalSection(context);

    /* isReset must be false already */
    Assert(!context->isReset);

    ret = context->methods->realloc(context, pointer, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);

    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;

    AssertArg(MemoryContextIsValid(context));
    AssertNotInCriticalSection(context);

    if (!AllocHugeSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    context->isReset = false;

    ret = context->methods->alloc(context, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    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)
{
    MemoryContext context = GetMemoryChunkContext(pointer);
    void       *ret;

    if (!AllocHugeSizeIsValid(size))
        elog(ERROR, "invalid memory alloc request size %zu", size);

    AssertNotInCriticalSection(context);

    /* isReset must be false already */
    Assert(!context->isReset);

    ret = context->methods->realloc(context, pointer, size);
    if (unlikely(ret == NULL))
    {
        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)));
    }

    VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);

    return ret;
}

/*
 * 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);
}