mcxt.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/mcxt.c,v 1.56 2005/10/15 02:49:36 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "nodes/memnodes.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;

/* These two are transient links to contexts owned by other objects: */
MemoryContext QueryContext = NULL;
MemoryContext PortalContext = NULL;


/*****************************************************************************
 *	  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).
 *
 * In a standalone backend this must be called during backend startup.
 */
void
MemoryContextInit(void)
{
	AssertState(TopMemoryContext == NULL);

	/*
	 * Initialize TopMemoryContext as an AllocSetContext with slow growth rate
	 * --- we don't really expect much to be allocated in it.
	 *
	 * (There is special-case code in MemoryContextCreate() for this call.)
	 */
	TopMemoryContext = AllocSetContextCreate((MemoryContext) NULL,
											 "TopMemoryContext",
											 0,
											 8 * 1024,
											 8 * 1024);

	/*
	 * 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!
	 */
	ErrorContext = AllocSetContextCreate(TopMemoryContext,
										 "ErrorContext",
										 8 * 1024,
										 8 * 1024,
										 8 * 1024);
}

/*
 * MemoryContextReset
 *		Release all space allocated within a context and its descendants,
 *		but don't delete the contexts themselves.
 *
 * The type-specific reset routine handles the context itself, but we
 * have to do the recursion for the children.
 */
void
MemoryContextReset(MemoryContext context)
{
	AssertArg(MemoryContextIsValid(context));

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

	(*context->methods->reset) (context);
}

/*
 * 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)
		MemoryContextReset(child);
}

/*
 * MemoryContextDelete
 *		Delete a context and its descendants, and release all space
 *		allocated therein.
 *
 * The type-specific delete routine removes all subsidiary storage
 * for the context, but we have to delete the context node itself,
 * as well as recurse to get the children.	We must also delink the
 * node 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);

	MemoryContextDeleteChildren(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.
	 */
	if (context->parent)
	{
		MemoryContext parent = context->parent;

		if (context == parent->firstchild)
			parent->firstchild = context->nextchild;
		else
		{
			MemoryContext child;

			for (child = parent->firstchild; child; child = child->nextchild)
			{
				if (context == child->nextchild)
				{
					child->nextchild = context->nextchild;
					break;
				}
			}
		}
	}
	(*context->methods->delete) (context);
	pfree(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);
}

/*
 * MemoryContextResetAndDeleteChildren
 *		Release all space allocated within a context and delete all
 *		its descendants.
 *
 * This is a common combination case where we want to preserve the
 * specific context but get rid of absolutely everything under it.
 */
void
MemoryContextResetAndDeleteChildren(MemoryContext context)
{
	AssertArg(MemoryContextIsValid(context));

	MemoryContextDeleteChildren(context);
	(*context->methods->reset) (context);
}

/*
 * 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)
{
	StandardChunkHeader *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 != NULL);
	Assert(pointer == (void *) MAXALIGN(pointer));

	/*
	 * OK, it's probably safe to look at the chunk header.
	 */
	header = (StandardChunkHeader *)
		((char *) pointer - STANDARDCHUNKHEADERSIZE);

	AssertArg(MemoryContextIsValid(header->context));

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

/*
 * GetMemoryChunkContext
 *		Given a currently-allocated chunk, determine the context
 *		it belongs to.
 */
MemoryContext
GetMemoryChunkContext(void *pointer)
{
	StandardChunkHeader *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 != NULL);
	Assert(pointer == (void *) MAXALIGN(pointer));

	/*
	 * OK, it's probably safe to look at the chunk header.
	 */
	header = (StandardChunkHeader *)
		((char *) pointer - STANDARDCHUNKHEADERSIZE);

	AssertArg(MemoryContextIsValid(header->context));

	return header->context;
}

/*
 * 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);
}

/*
 * MemoryContextStats
 *		Print statistics about the named context and all its descendants.
 *
 * This is just a debugging utility, so it's not fancy.  The statistics
 * are merely sent to stderr.
 */
void
MemoryContextStats(MemoryContext context)
{
	MemoryContext child;

	AssertArg(MemoryContextIsValid(context));

	(*context->methods->stats) (context);
	for (child = context->firstchild; child != NULL; child = child->nextchild)
		MemoryContextStats(child);
}


/*
 * 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));