/*--------------------------------------------------------------------
 * Symbols referenced in this file:
 * - ErrorContext
 * - MemoryContextReset
 * - MemoryContextDeleteChildren
 * - MemoryContextDelete
 * - MemoryContextSetParent
 * - pfree
 * - MemoryContextCallResetCallbacks
 * - MemoryContextResetOnly
 * - repalloc
 * - MemoryContextStats
 * - MemoryContextStatsInternal
 * - TopMemoryContext
 * - pstrdup
 * - MemoryContextStrdup
 * - MemoryContextAlloc
 * - CurrentMemoryContext
 * - palloc
 * - MemoryContextAllocZeroAligned
 * - MemoryContextAllocZero
 * - palloc0
 * - MemoryContextCreate
 * - MemoryContextInit
 * - MemoryContextAllowInCriticalSection
 * - CurrentMemoryContext
 * - MemoryContextDelete
 * - palloc0
 *--------------------------------------------------------------------
 */

/*-------------------------------------------------------------------------
 *
 * 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) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/utils/mmgr/mcxt.c
 *
 *-------------------------------------------------------------------------
 */

/* see palloc.h.  Must be before postgres.h */
#define MCXT_INCLUDE_DEFINITIONS

#include "postgres.h"

#include "miscadmin.h"
#include "utils/memdebug.h"
#include "utils/memutils.h"


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

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

__thread MemoryContext ErrorContext = NULL;







/* This is a transient link to the active portal's memory context: */


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

/*
 * 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);

	/*
	 * 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,
											 0,
											 0);

	/*
	 * 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",
										 0,
										 0,
										 0);
	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);
		(*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.
 */


/*
 * 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);

	/*
	 * 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);

	(*context->methods->delete_context) (context);
	VALGRIND_DESTROY_MEMPOOL(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);
}

/*
 * 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.
 */


/*
 * 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);
	}
}

/*
 * 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 == 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;
				}
			}
		}
	}

	/* And relink */
	if (new_parent)
	{
		AssertArg(MemoryContextIsValid(new_parent));
		context->parent = new_parent;
		context->nextchild = new_parent->firstchild;
		new_parent->firstchild = context;
	}
	else
	{
		context->parent = 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.
 */


/*
 * GetMemoryChunkContext
 *		Given a currently-allocated chunk, determine the context
 *		it belongs to.
 */


/*
 * MemoryContextGetParent
 *		Get the parent context (if any) of the specified context
 */


/*
 * MemoryContextIsEmpty
 *		Is a memory context empty of any allocated space?
 */


/*
 * 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)
{
	MemoryContextStatsInternal(context, 0);
}

static void
MemoryContextStatsInternal(MemoryContext context, int level)
{
	MemoryContext child;

	AssertArg(MemoryContextIsValid(context));

	(*context->methods->stats) (context, level);
	for (child = context->firstchild; child != NULL; child = child->nextchild)
		MemoryContextStatsInternal(child, level + 1);
}

/*
 * 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.
 */


/*--------------------
 * 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 ereport() 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;

	/* creating new memory contexts is not allowed in a critical section */
	Assert(CritSectionCount == 0);

	/* 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->isReset = true;
	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) */
	/* Could use MemoryContextSetParent here, but doesn't seem worthwhile */
	if (parent)
	{
		node->parent = parent;
		node->nextchild = parent->firstchild;
		parent->firstchild = node;
		/* inherit allowInCritSection flag from parent */
		node->allowInCritSection = parent->allowInCritSection;
	}

	VALGRIND_CREATE_MEMPOOL(node, 0, false);

	/* 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)
{
	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 (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	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 (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	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 (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	VALGRIND_MEMPOOL_ALLOC(context, ret, size);

	MemSetLoop(ret, 0, size);

	return ret;
}

/*
 * MemoryContextAllocExtended
 *		Allocate space within the specified context using the given flags.
 */


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

	AssertArg(MemoryContextIsValid(CurrentMemoryContext));
	AssertNotInCriticalSection(CurrentMemoryContext);

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

	CurrentMemoryContext->isReset = false;

	ret = (*CurrentMemoryContext->methods->alloc) (CurrentMemoryContext, size);
	if (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	VALGRIND_MEMPOOL_ALLOC(CurrentMemoryContext, ret, size);

	return ret;
}

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

	AssertArg(MemoryContextIsValid(CurrentMemoryContext));
	AssertNotInCriticalSection(CurrentMemoryContext);

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

	CurrentMemoryContext->isReset = false;

	ret = (*CurrentMemoryContext->methods->alloc) (CurrentMemoryContext, size);
	if (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	VALGRIND_MEMPOOL_ALLOC(CurrentMemoryContext, ret, size);

	MemSetAligned(ret, 0, size);

	return ret;
}



/*
 * pfree
 *		Release an allocated chunk.
 */
void
pfree(void *pointer)
{
	MemoryContext 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.
	 */
	Assert(pointer != NULL);
	Assert(pointer == (void *) MAXALIGN(pointer));

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

	AssertArg(MemoryContextIsValid(context));

	(*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;
	void	   *ret;

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

	/*
	 * 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.
	 */
	context = ((StandardChunkHeader *)
			   ((char *) pointer - STANDARDCHUNKHEADERSIZE))->context;

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

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

	ret = (*context->methods->realloc) (context, pointer, size);
	if (ret == NULL)
	{
		MemoryContextStats(TopMemoryContext);
		ereport(ERROR,
				(errcode(ERRCODE_OUT_OF_MEMORY),
				 errmsg("out of memory"),
				 errdetail("Failed on request of size %zu.", size)));
	}

	VALGRIND_MEMPOOL_CHANGE(context, pointer, ret, size);

	return ret;
}

/*
 * MemoryContextAllocHuge
 *		Allocate (possibly-expansive) space within the specified context.
 *
 * See considerations in comment at MaxAllocHugeSize.
 */


/*
 * repalloc_huge
 *		Adjust the size of a previously allocated chunk, permitting a large
 *		value.  The previous allocation need not have been "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.
 */

