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Adjust nodeFunctionscan.c to reset transient memory context between calls

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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.
This commit is contained in:
Tom Lane
2002-08-29 17:14:33 +00:00
parent 0201dac1c3
commit e4186762ff
10 changed files with 154 additions and 134 deletions
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46
doc/src/sgml/xfunc.sgml
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@@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.57 2002/08/29 00:17:02 tgl Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.58 2002/08/29 17:14:32 tgl Exp $
-->
<chapter id="xfunc">
@@ -1670,13 +1670,14 @@ typedef struct
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;
</programlisting>
@@ -1714,27 +1715,43 @@ SRF_RETURN_DONE(funcctx)
to clean up and end the SRF.
</para>
<para>
The palloc memory context that is current when the SRF is called is
a transient context that will be cleared between calls. This means
that you do not need to be careful about pfree'ing everything
you palloc; it will go away anyway. However, if you want to allocate
any data structures to live across calls, you need to put them somewhere
else. The memory context referenced by
<structfield>multi_call_memory_ctx</> is a suitable location for any
data that needs to survive until the SRF is finished running. In most
cases, this means that you should switch into
<structfield>multi_call_memory_ctx</> while doing the first-call setup.
</para>
<para>
A complete pseudo-code example looks like the following:
<programlisting>
Datum
my_Set_Returning_Function(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
Datum result;
FuncCallContext *funcctx;
Datum result;
MemoryContext oldcontext;
[user defined declarations]
if (SRF_IS_FIRSTCALL())
{
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
/* one-time setup code appears here: */
[user defined code]
funcctx = SRF_FIRSTCALL_INIT();
[if returning composite]
[build TupleDesc, and perhaps AttInMetadata]
[obtain slot]
funcctx-&gt;slot = slot;
[endif returning composite]
[user defined code]
MemoryContextSwitchTo(oldcontext);
}
/* each-time setup code appears here: */
@@ -1777,8 +1794,13 @@ testpassbyval(PG_FUNCTION_ARGS)
/* stuff done only on the first call of the function */
if (SRF_IS_FIRSTCALL())
{
MemoryContext oldcontext;
/* create a function context for cross-call persistence */
funcctx = SRF_FIRSTCALL_INIT();
funcctx = SRF_FIRSTCALL_INIT();
/* switch to memory context appropriate for multiple function calls */
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
/* total number of tuples to be returned */
funcctx-&gt;max_calls = PG_GETARG_UINT32(0);
@@ -1800,6 +1822,8 @@ testpassbyval(PG_FUNCTION_ARGS)
*/
attinmeta = TupleDescGetAttInMetadata(tupdesc);
funcctx-&gt;attinmeta = attinmeta;
MemoryContextSwitchTo(oldcontext);
}
/* stuff done on every call of the function */
@@ -1836,7 +1860,7 @@ testpassbyval(PG_FUNCTION_ARGS)
/* make the tuple into a datum */
result = TupleGetDatum(slot, tuple);
/* Clean up */
/* Clean up (this is not actually necessary) */
pfree(values[0]);
pfree(values[1]);
pfree(values[2]);