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, 21 insertions, 9 deletions

diff --git a/src/pl/plpython/plpy_cursorobject.c b/src/pl/plpython/plpy_cursorobject.c
index 2c458d35fdb..103571ba15c 100644
--- a/src/pl/plpython/plpy_cursorobject.c
+++ b/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);
 }