Tweak palloc/repalloc to allow zero bytes to be requested, as per recent

proposal.  Eliminate several dozen now-unnecessary hacks to avoid palloc(0).
(It's likely there are more that I didn't find.)

3 files changed, 25 insertions, 7 deletions

diff --git a/src/backend/utils/adt/name.c b/src/backend/utils/adt/name.c
index ecac8d2d50..cf4f14c3e1 100644
--- a/src/backend/utils/adt/name.c
+++ b/src/backend/utils/adt/name.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/name.c,v 1.52 2004/05/30 23:40:35 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/name.c,v 1.53 2004/06/05 19:48:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -358,9 +358,7 @@ current_schemas(PG_FUNCTION_ARGS)
 	int			i;
 	ArrayType  *array;
 
-	/* +1 here is just to avoid palloc(0) error */
-
-	names = (Datum *) palloc((list_length(search_path) + 1) * sizeof(Datum));
+	names = (Datum *) palloc(list_length(search_path) * sizeof(Datum));
 	i = 0;
 	foreach(l, search_path)
 	{
diff --git a/src/backend/utils/mmgr/README b/src/backend/utils/mmgr/README
index 409cfd768c..f705827c1b 100644
--- a/src/backend/utils/mmgr/README
+++ b/src/backend/utils/mmgr/README
@@ -1,4 +1,4 @@
-$PostgreSQL: pgsql/src/backend/utils/mmgr/README,v 1.5 2003/11/29 19:52:04 pgsql Exp $
+$PostgreSQL: pgsql/src/backend/utils/mmgr/README,v 1.6 2004/06/05 19:48:09 tgl Exp $
 
 Notes about memory allocation redesign
 --------------------------------------
@@ -53,6 +53,26 @@ that can be reset or deleted at strategic times within a query, such as
 after each tuple.
 
 
+Some notes about the palloc API versus standard C library
+---------------------------------------------------------
+
+The behavior of palloc and friends is similar to the standard C library's
+malloc and friends, but there are some deliberate differences too.  Here
+are some notes to clarify the behavior.
+
+* If out of memory, palloc and repalloc exit via elog(ERROR).  They never
+return NULL, and it is not necessary or useful to test for such a result.
+
+* palloc(0) is explicitly a valid operation.  It does not return a NULL
+pointer, but a valid chunk of which no bytes may be used.  (However, the
+chunk might later be repalloc'd larger; it can also be pfree'd without
+error.)  (Note: this behavior is new in Postgres 7.5; earlier versions
+disallowed palloc(0).  It seems more consistent to allow it, however.)
+Similarly, repalloc allows realloc'ing to zero size.
+
+* pfree and repalloc do not accept a NULL pointer.  This is intentional.
+
+
 pfree/repalloc no longer depend on CurrentMemoryContext
 -------------------------------------------------------
 
diff --git a/src/backend/utils/mmgr/mcxt.c b/src/backend/utils/mmgr/mcxt.c
index bc139a7d96..c444886e14 100644
--- a/src/backend/utils/mmgr/mcxt.c
+++ b/src/backend/utils/mmgr/mcxt.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/mcxt.c,v 1.44 2003/11/29 19:52:04 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/mmgr/mcxt.c,v 1.45 2004/06/05 19:48:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -565,7 +565,7 @@ pfree(void *pointer)
 
 /*
  * repalloc
- *
+ *		Adjust the size of a previously allocated chunk.
  */
 void *
 repalloc(void *pointer, Size size)