Adjust nodeFunctionscan.c to reset transient memory context between calls

to the table function, thus preventing memory leakage accumulation across
calls.  This means that SRFs need to be careful to distinguish permanent
and local storage; adjust code and documentation accordingly.  Patch by
Joe Conway, very minor tweaks by Tom Lane.

1 files changed, 14 insertions, 8 deletions

diff --git a/src/include/funcapi.h b/src/include/funcapi.h
index 27dbdf20e62..fcfb6acb694 100644
--- a/src/include/funcapi.h
+++ b/src/include/funcapi.h
@@ -9,7 +9,7 @@
  *
  * Copyright (c) 2002, PostgreSQL Global Development Group
  *
- * $Id: funcapi.h,v 1.5 2002/08/29 00:17:06 tgl Exp $
+ * $Id: funcapi.h,v 1.6 2002/08/29 17:14:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -101,13 +101,14 @@ typedef struct FuncCallContext
 	AttInMetadata	   *attinmeta;
 
 	/*
-	 * memory context used to initialize structure
+	 * memory context used for structures which must live for multiple calls
 	 *
-	 * fmctx is set by SRF_FIRSTCALL_INIT() for you, and used by
-	 * SRF_RETURN_DONE() for cleanup. It is primarily for internal use
-	 * by the API.
+	 * multi_call_memory_ctx is set by SRF_FIRSTCALL_INIT() for you, and used
+	 * by SRF_RETURN_DONE() for cleanup. It is the most appropriate memory
+	 * context for any memory that is to be re-used across multiple calls
+	 * of the SRF.
 	 */
-	MemoryContext	fmctx;
+	MemoryContext	multi_call_memory_ctx;
 
 }	FuncCallContext;
 
@@ -160,17 +161,22 @@ extern HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
  * {
  * 	FuncCallContext	   *funcctx;
  * 	Datum				result;
+ *  MemoryContext		oldcontext;
  * 	<user defined declarations>
  * 
- * 	if(SRF_IS_FIRSTCALL())
+ * 	if (SRF_IS_FIRSTCALL())
  * 	{
- * 		<user defined code>
  * 		funcctx = SRF_FIRSTCALL_INIT();
+ *		// switch context when allocating stuff to be used in later calls
+ *		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+ * 		<user defined code>
  * 		<if returning composite>
  * 			<obtain slot>
  * 			funcctx->slot = slot;
  * 		<endif returning composite>
  * 		<user defined code>
+ *		// return to original context when allocating transient memory
+ *		MemoryContextSwitchTo(oldcontext);
  *  }
  * 	<user defined code>
  * 	funcctx = SRF_PERCALL_SETUP();