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

Author: tglsfdc

src/pl/plpython/plpy_cursorobject.c

@@ -8,6 +8,7 @@
 
 #include "access/xact.h"
 #include "mb/pg_wchar.h"
+#include "utils/memutils.h"
 
 #include "plpython.h"
 
@@ -111,7 +112,12 @@ PLy_cursor_query(const char *query)
 		return NULL;
 	cursor->portalname = NULL;
 	cursor->closed = false;
-	PLy_typeinfo_init(&cursor->result);
+	cursor->mcxt = AllocSetContextCreate(TopMemoryContext,
+										 "PL/Python cursor context",
+										 ALLOCSET_DEFAULT_MINSIZE,
+										 ALLOCSET_DEFAULT_INITSIZE,
+										 ALLOCSET_DEFAULT_MAXSIZE);
+	PLy_typeinfo_init(&cursor->result, cursor->mcxt);
 
 	oldcontext = CurrentMemoryContext;
 	oldowner = CurrentResourceOwner;
@@ -139,7 +145,7 @@ PLy_cursor_query(const char *query)
 			elog(ERROR, "SPI_cursor_open() failed: %s",
 				 SPI_result_code_string(SPI_result));
 
-		cursor->portalname = PLy_strdup(portal->name);
+		cursor->portalname = MemoryContextStrdup(cursor->mcxt, portal->name);
 
 		PLy_spi_subtransaction_commit(oldcontext, oldowner);
 	}
@@ -200,7 +206,12 @@ PLy_cursor_plan(PyObject *ob, PyObject *args)
 		return NULL;
 	cursor->portalname = NULL;
 	cursor->closed = false;
-	PLy_typeinfo_init(&cursor->result);
+	cursor->mcxt = AllocSetContextCreate(TopMemoryContext,
+										 "PL/Python cursor context",
+										 ALLOCSET_DEFAULT_MINSIZE,
+										 ALLOCSET_DEFAULT_INITSIZE,
+										 ALLOCSET_DEFAULT_MAXSIZE);
+	PLy_typeinfo_init(&cursor->result, cursor->mcxt);
 
 	oldcontext = CurrentMemoryContext;
 	oldowner = CurrentResourceOwner;
@@ -261,7 +272,7 @@ PLy_cursor_plan(PyObject *ob, PyObject *args)
 			elog(ERROR, "SPI_cursor_open() failed: %s",
 				 SPI_result_code_string(SPI_result));
 
-		cursor->portalname = PLy_strdup(portal->name);
+		cursor->portalname = MemoryContextStrdup(cursor->mcxt, portal->name);
 
 		PLy_spi_subtransaction_commit(oldcontext, oldowner);
 	}
@@ -315,12 +326,13 @@ PLy_cursor_dealloc(PyObject *arg)
 
 		if (PortalIsValid(portal))
 			SPI_cursor_close(portal);
+		cursor->closed = true;
+	}
+	if (cursor->mcxt)
+	{
+		MemoryContextDelete(cursor->mcxt);
+		cursor->mcxt = NULL;
 	}
-
-	PLy_free(cursor->portalname);
-	cursor->portalname = NULL;
-
-	PLy_typeinfo_dealloc(&cursor->result);
 	arg->ob_type->tp_free(arg);
 }
 

src/pl/plpython/plpy_cursorobject.h

@@ -14,6 +14,7 @@ typedef struct PLyCursorObject
 	char	   *portalname;
 	PLyTypeInfo result;
 	bool		closed;
+	MemoryContext mcxt;
 } PLyCursorObject;
 
 extern void PLy_cursor_init_type(void);

src/pl/plpython/plpy_exec.c

@@ -852,6 +852,6 @@ PLy_abort_open_subtransactions(int save_subxact_level)
 
 		MemoryContextSwitchTo(subtransactiondata->oldcontext);
 		CurrentResourceOwner = subtransactiondata->oldowner;
-		PLy_free(subtransactiondata);
+		pfree(subtransactiondata);
 	}
 }

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);
 }

src/pl/plpython/plpy_main.h

@@ -25,4 +25,7 @@ typedef struct PLyExecutionContext
 /* Get the current execution context */
 extern PLyExecutionContext *PLy_current_execution_context(void);
 
+/* Get the scratch memory context for specified execution context */
+extern MemoryContext PLy_get_scratch_context(PLyExecutionContext *context);
+
 #endif   /* PLPY_MAIN_H */

src/pl/plpython/plpy_planobject.c

@@ -11,6 +11,7 @@
 #include "plpy_planobject.h"
 
 #include "plpy_elog.h"
+#include "utils/memutils.h"
 
 
 static void PLy_plan_dealloc(PyObject *arg);
@@ -80,6 +81,7 @@ PLy_plan_new(void)
 	ob->types = NULL;
 	ob->values = NULL;
 	ob->args = NULL;
+	ob->mcxt = NULL;
 
 	return (PyObject *) ob;
 }
@@ -96,20 +98,15 @@ PLy_plan_dealloc(PyObject *arg)
 	PLyPlanObject *ob = (PLyPlanObject *) arg;
 
 	if (ob->plan)
+	{
 		SPI_freeplan(ob->plan);
-	if (ob->types)
-		PLy_free(ob->types);
-	if (ob->values)
-		PLy_free(ob->values);
-	if (ob->args)
+		ob->plan = NULL;
+	}
+	if (ob->mcxt)
 	{
-		int			i;
-
-		for (i = 0; i < ob->nargs; i++)
-			PLy_typeinfo_dealloc(&ob->args[i]);
-		PLy_free(ob->args);
+		MemoryContextDelete(ob->mcxt);
+		ob->mcxt = NULL;
 	}
-
 	arg->ob_type->tp_free(arg);
 }
 

src/pl/plpython/plpy_planobject.h

@@ -17,6 +17,7 @@ typedef struct PLyPlanObject
 	Oid		   *types;
 	Datum	   *values;
 	PLyTypeInfo *args;
+	MemoryContext mcxt;
 } PLyPlanObject;
 
 extern void PLy_plan_init_type(void);