/*-------------------------------------------------------------------------
 *
 * 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) 1996-2001, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/utils/mmgr/mcxt.c,v 1.29 2001/10/25 05:49:51 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "nodes/memnodes.h"
#include "utils/excid.h"
#include "utils/memutils.h"


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

/*
 * CurrentMemoryContext
 *		Default memory context for allocations.
 */
MemoryContext CurrentMemoryContext = NULL;

/*
 * Standard top-level contexts
 */
MemoryContext TopMemoryContext = NULL;
MemoryContext ErrorContext = NULL;
MemoryContext PostmasterContext = NULL;
MemoryContext CacheMemoryContext = NULL;
MemoryContext QueryContext = NULL;
MemoryContext TopTransactionContext = NULL;
MemoryContext TransactionCommandContext = 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",
											 8 * 1024,
											 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));

	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);
}

/*
 * 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));

	(*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)
{
	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.
	 */
	if (pointer == NULL || pointer != (void *) MAXALIGN(pointer))
		return false;

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

	/*
	 * If the context link doesn't match then we certainly have a
	 * non-member chunk.  Also check for a reasonable-looking size as
	 * extra guard against being fooled by bogus pointers.
	 */
	if (header->context == context && AllocSizeIsValid(header->size))
		return true;
	return false;
}

/*--------------------
 * 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 context creation procedure is a little bit tricky because
 * we want to be sure that we don't leave the context tree invalid
 * in case of failure (such as insufficient memory to allocate the
 * context node itself).  The procedure goes like this:
 *	1.	Context-type-specific routine first calls MemoryContextCreate(),
 *		passing the appropriate tag/size/methods values (the methods
 *		pointer will ordinarily point to statically allocated data).
 *		The parent and name parameters usually come from the caller.
 *	2.	MemoryContextCreate() attempts to allocate the context node,
 *		plus space for the name.  If this fails we can elog() with no
 *		damage done.
 *	3.	We fill in all of the type-independent MemoryContext fields.
 *	4.	We call the type-specific init routine (using the methods pointer).
 *		The init routine is required to make the node minimally valid
 *		with zero chance of failure --- it can't allocate more memory,
 *		for example.
 *	5.	Now we have a minimally valid node that can behave correctly
 *		when told to reset or delete itself.  We link the node to its
 *		parent (if any), making the node part of the context tree.
 *	6.	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.
 *
 * This protocol doesn't prevent us from leaking memory if step 6 fails
 * during creation of a top-level context, since there's no parent link
 * in that case.  However, if you run out of memory while you're building
 * a top-level context, you might as well go home anyway...
 *
 * Normally, the context node and the name are allocated from
 * TopMemoryContext (NOT from the parent context, since the node must
 * survive resets of its parent context!).	However, this routine is itself
 * used to create TopMemoryContext!  If we see that TopMemoryContext is NULL,
 * we assume we are creating TopMemoryContext and use malloc() to allocate
 * the node.
 *
 * Note that the name field of a MemoryContext does not point to
 * separately-allocated storage, so it should not be freed at context
 * deletion.
 *--------------------
 */
MemoryContext
MemoryContextCreate(NodeTag tag, Size size,
					MemoryContextMethods *methods,
					MemoryContext parent,
					const char *name)
{
	MemoryContext node;
	Size		needed = size + strlen(name) + 1;

	/* Get space for node and name */
	if (TopMemoryContext != NULL)
	{
		/* Normal case: allocate the node in TopMemoryContext */
		node = (MemoryContext) MemoryContextAlloc(TopMemoryContext,
												  needed);
	}
	else
	{
		/* Special case for startup: use good ol' malloc */
		node = (MemoryContext) malloc(needed);
		Assert(node != NULL);
	}

	/* Initialize the node as best we can */
	MemSet(node, 0, size);
	node->type = tag;
	node->methods = methods;
	node->parent = NULL;		/* for the moment */
	node->firstchild = NULL;
	node->nextchild = NULL;
	node->name = ((char *) node) + size;
	strcpy(node->name, name);

	/* Type-specific routine finishes any other essential initialization */
	(*node->methods->init) (node);

	/* OK to link node to parent (if any) */
	if (parent)
	{
		node->parent = parent;
		node->nextchild = parent->firstchild;
		parent->firstchild = node;
	}

	/* Return to type-specific creation routine to finish up */
	return node;
}

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

	if (!AllocSizeIsValid(size))
		elog(ERROR, "MemoryContextAlloc: invalid request size %lu",
			 (unsigned long) size);

	return (*context->methods->alloc) (context, size);
}

/*
 * pfree
 *		Release an allocated chunk.
 */
void
pfree(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));

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

/*
 * repalloc
 *
 */
void *
repalloc(void *pointer, Size size)
{
	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));

	if (!AllocSizeIsValid(size))
		elog(ERROR, "repalloc: invalid request size %lu",
			 (unsigned long) size);

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

/*
 * MemoryContextSwitchTo
 *		Returns the current context; installs the given context.
 */
MemoryContext
MemoryContextSwitchTo(MemoryContext context)
{
	MemoryContext old;

	AssertArg(MemoryContextIsValid(context));

	old = CurrentMemoryContext;
	CurrentMemoryContext = context;
	return old;
}

/*
 * 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;
}
