Fix memory leaks in PL/Python.

Previously, plpython was in the habit of allocating a lot of stuff in
TopMemoryContext, and it was very slipshod about making sure that stuff
got cleaned up; in particular, use of TopMemoryContext as fn_mcxt for
function calls represents an unfixable leak, since we generally don't
know what the called function might have allocated in fn_mcxt.  This
results in session-lifespan leakage in certain usage scenarios, as for
example in a case reported by Ed Behn back in July.

To fix, get rid of all the retail allocations in TopMemoryContext.
All long-lived allocations are now made in sub-contexts that are
associated with specific objects (either pl/python procedures, or
Python-visible objects such as cursors and plans).  We can clean these
up when the associated object is deleted.

I went so far as to get rid of PLy_malloc completely.  There were a
couple of places where it could still have been used safely, but on
the whole it was just an invitation to bad coding.

Haribabu Kommi, based on a draft patch by Heikki Linnakangas;
some further work by me

1 files changed, 30 insertions, 9 deletions

diff --git a/src/pl/plpython/plpy_main.c b/src/pl/plpython/plpy_main.c
index 63a284e2384..3c2ebfa16af 100644
--- a/src/pl/plpython/plpy_main.c
+++ b/src/pl/plpython/plpy_main.c
@@ -277,7 +277,12 @@ plpython_inline_handler(PG_FUNCTION_ARGS)
 	flinfo.fn_mcxt = CurrentMemoryContext;
 
 	MemSet(&proc, 0, sizeof(PLyProcedure));
-	proc.pyname = PLy_strdup("__plpython_inline_block");
+	proc.mcxt = AllocSetContextCreate(TopMemoryContext,
+									  "__plpython_inline_block",
+									  ALLOCSET_DEFAULT_MINSIZE,
+									  ALLOCSET_DEFAULT_INITSIZE,
+									  ALLOCSET_DEFAULT_MAXSIZE);
+	proc.pyname = MemoryContextStrdup(proc.mcxt, "__plpython_inline_block");
 	proc.langid = codeblock->langOid;
 	proc.result.out.d.typoid = VOIDOID;
 
@@ -364,17 +369,32 @@ PLy_current_execution_context(void)
 	return PLy_execution_contexts;
 }
 
+MemoryContext
+PLy_get_scratch_context(PLyExecutionContext *context)
+{
+	/*
+	 * A scratch context might never be needed in a given plpython procedure,
+	 * so allocate it on first request.
+	 */
+	if (context->scratch_ctx == NULL)
+		context->scratch_ctx =
+			AllocSetContextCreate(TopTransactionContext,
+								  "PL/Python scratch context",
+								  ALLOCSET_DEFAULT_MINSIZE,
+								  ALLOCSET_DEFAULT_INITSIZE,
+								  ALLOCSET_DEFAULT_MAXSIZE);
+	return context->scratch_ctx;
+}
+
 static PLyExecutionContext *
 PLy_push_execution_context(void)
 {
-	PLyExecutionContext *context = PLy_malloc(sizeof(PLyExecutionContext));
+	PLyExecutionContext *context;
 
+	context = (PLyExecutionContext *)
+		MemoryContextAlloc(TopTransactionContext, sizeof(PLyExecutionContext));
 	context->curr_proc = NULL;
-	context->scratch_ctx = AllocSetContextCreate(TopTransactionContext,
-												 "PL/Python scratch context",
-												 ALLOCSET_DEFAULT_MINSIZE,
-												 ALLOCSET_DEFAULT_INITSIZE,
-												 ALLOCSET_DEFAULT_MAXSIZE);
+	context->scratch_ctx = NULL;
 	context->next = PLy_execution_contexts;
 	PLy_execution_contexts = context;
 	return context;
@@ -390,6 +410,7 @@ PLy_pop_execution_context(void)
 
 	PLy_execution_contexts = context->next;
 
-	MemoryContextDelete(context->scratch_ctx);
-	PLy_free(context);
+	if (context->scratch_ctx)
+		MemoryContextDelete(context->scratch_ctx);
+	pfree(context);
 }