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Code review for palloc0 patch --- avoid dangerous and unnecessary

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practice of evaluating MemSet's arguments multiple times, except for
the special case of newNode(), where we can assume the argument is
a constant sizeof() operator.
Also, add GetMemoryChunkContext() to mcxt.c's API, in preparation for
fixing recent GEQO breakage.
This commit is contained in:
Tom Lane
2002-12-16 16:22:46 +00:00
parent e64c7feb2f
commit 88177f77b1
6 changed files with 160 additions and 52 deletions
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16
src/include/nodes/nodes.h
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: nodes.h,v 1.133 2002/12/14 00:17:59 tgl Exp $
* $Id: nodes.h,v 1.134 2002/12/16 16:22:46 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -293,9 +293,16 @@ typedef struct Node
#define nodeTag(nodeptr) (((Node*)(nodeptr))->type)
/*
* newNode -
* create a new node of the specified size and tag the node with the
* specified tag.
*
* !WARNING!: Avoid using newNode directly. You should be using the
* macro makeNode. eg. to create a Query node, use makeNode(Query)
*
* There is no way to dereference the palloc'ed pointer to assign the
* tag, and return the pointer itself, so we need a holder variable.
* Fortunately, this function isn't recursive so we just define
* tag, and also return the pointer itself, so we need a holder variable.
* Fortunately, this macro isn't recursive so we just define
* a global variable for this purpose.
*/
extern Node *newNodeMacroHolder;
@ -303,8 +310,7 @@ extern Node *newNodeMacroHolder;
#define newNode(size, tag) \
( \
AssertMacro((size) >= sizeof(Node)), /* need the tag, at least */ \
\
newNodeMacroHolder = (Node *) palloc0(size), \
newNodeMacroHolder = (Node *) palloc0fast(size), \
newNodeMacroHolder->type = (tag), \
newNodeMacroHolder \
)