Fix PL/Python for recursion and interleaved set-returning functions.

PL/Python failed if a PL/Python function was invoked recursively via SPI,
since arguments are passed to the function in its global dictionary
(a horrible decision that's far too ancient to undo) and it would delete
those dictionary entries on function exit, leaving the outer recursion
level(s) without any arguments.  Not deleting them would be little better,
since the outer levels would then see the innermost level's arguments.

Since PL/Python uses ValuePerCall mode for evaluating set-returning
functions, it's possible for multiple executions of the same SRF to be
interleaved within a query.  PL/Python failed in such a case, because
it stored only one iterator per function, directly in the function's
PLyProcedure struct.  Moreover, one interleaved instance of the SRF
would see argument values that should belong to another.

Hence, invent code for saving and restoring the argument entries.  To fix
the recursion case, we only need to save at recursive entry and restore
at recursive exit, so the overhead in non-recursive cases is negligible.
To fix the SRF case, we have to save when suspending a SRF and restore
when resuming it, which is potentially not negligible; but fortunately
this is mostly a matter of manipulating Python object refcounts and
should not involve much physical data copying.

Also, store the Python iterator and saved argument values in a structure
associated with the SRF call site rather than the function itself.  This
requires adding a memory context deletion callback to ensure that the SRF
state is cleaned up if the calling query exits before running the SRF to
completion.  Without that we'd leak a refcount to the iterator object in
such a case, resulting in session-lifespan memory leakage.  (In the
pre-existing code, there was no memory leak because there was only one
iterator pointer, but what would happen is that the previous iterator
would be resumed by the next query attempting to use the SRF.  Hardly the
semantics we want.)

We can buy back some of whatever overhead we've added by getting rid of
PLy_function_delete_args(), which seems a useless activity: there is no
need to delete argument entries from the global dictionary on exit,
since the next time anyone would see the global dict is on the next
fresh call of the PL/Python function, at which time we'd overwrite those
entries with new arg values anyway.

Also clean up some really ugly coding in the SRF implementation, including
such gems as returning directly out of a PG_TRY block.  (The only reason
that failed to crash hard was that all existing call sites immediately
exited their own PG_TRY blocks, popping the dangling longjmp pointer before
there was any chance of it being used.)

In principle this is a bug fix; but it seems a bit too invasive relative to
its value for a back-patch, and besides the fix depends on memory context
callbacks so it could not go back further than 9.5 anyway.

Alexey Grishchenko and Tom Lane

src/pl/plpython/expected/plpython_setof.out

@@ -124,6 +124,35 @@ SELECT test_setof_spi_in_iterator();
  World
 (4 rows)
 
+-- set-returning function that modifies its parameters
+CREATE OR REPLACE FUNCTION ugly(x int, lim int) RETURNS SETOF int AS $$
+global x
+while x <= lim:
+    yield x
+    x = x + 1
+$$ LANGUAGE plpythonu;
+SELECT ugly(1, 5);
+ ugly 
+------
+    1
+    2
+    3
+    4
+    5
+(5 rows)
+
+-- interleaved execution of such a function
+SELECT ugly(1,3), ugly(7,8);
+ ugly | ugly 
+------+------
+    1 |    7
+    2 |    8
+    3 |    7
+    1 |    8
+    2 |    7
+    3 |    8
+(6 rows)
+
 -- returns set of named-composite-type tuples
 CREATE OR REPLACE FUNCTION get_user_records()
 RETURNS SETOF users

src/pl/plpython/expected/plpython_spi.out

@@ -57,6 +57,15 @@ for r in rv:
 return seq
 '
 	LANGUAGE plpythonu;
+CREATE FUNCTION spi_recursive_sum(a int) RETURNS int
+	AS
+'r = 0
+if a > 1:
+    r = plpy.execute("SELECT spi_recursive_sum(%d) as a" % (a-1))[0]["a"]
+return a + r
+'
+	LANGUAGE plpythonu;
+--
 -- spi and nested calls
 --
 select nested_call_one('pass this along');
@@ -112,6 +121,12 @@ SELECT join_sequences(sequences) FROM sequences
 ----------------
 (0 rows)
 
+SELECT spi_recursive_sum(10);
+ spi_recursive_sum 
+-------------------
+                55
+(1 row)
+
 --
 -- plan and result objects
 --

src/pl/plpython/plpy_exec.c

@@ -26,8 +26,21 @@
 #include "plpy_subxactobject.h"
 
 
+/* saved state for a set-returning function */
+typedef struct PLySRFState
+{
+	PyObject   *iter;			/* Python iterator producing results */
+	PLySavedArgs *savedargs;	/* function argument values */
+	MemoryContextCallback callback;		/* for releasing refcounts when done */
+} PLySRFState;
+
 static PyObject *PLy_function_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc);
-static void PLy_function_delete_args(PLyProcedure *proc);
+static PLySavedArgs *PLy_function_save_args(PLyProcedure *proc);
+static void PLy_function_restore_args(PLyProcedure *proc, PLySavedArgs *savedargs);
+static void PLy_function_drop_args(PLySavedArgs *savedargs);
+static void PLy_global_args_push(PLyProcedure *proc);
+static void PLy_global_args_pop(PLyProcedure *proc);
+static void plpython_srf_cleanup_callback(void *arg);
 static void plpython_return_error_callback(void *arg);
 
 static PyObject *PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc,
@@ -36,7 +49,7 @@ static HeapTuple PLy_modify_tuple(PLyProcedure *proc, PyObject *pltd,
 				 TriggerData *tdata, HeapTuple otup);
 static void plpython_trigger_error_callback(void *arg);
 
-static PyObject *PLy_procedure_call(PLyProcedure *proc, char *kargs, PyObject *vargs);
+static PyObject *PLy_procedure_call(PLyProcedure *proc, const char *kargs, PyObject *vargs);
 static void PLy_abort_open_subtransactions(int save_subxact_level);
 
 
@@ -47,28 +60,65 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 	Datum		rv;
 	PyObject   *volatile plargs = NULL;
 	PyObject   *volatile plrv = NULL;
+	FuncCallContext *volatile funcctx = NULL;
+	PLySRFState *volatile srfstate = NULL;
 	ErrorContextCallback plerrcontext;
 
+	/*
+	 * If the function is called recursively, we must push outer-level
+	 * arguments into the stack.  This must be immediately before the PG_TRY
+	 * to ensure that the corresponding pop happens.
+	 */
+	PLy_global_args_push(proc);
+
 	PG_TRY();
 	{
-		if (!proc->is_setof || proc->setof == NULL)
+		if (proc->is_setof)
+		{
+			/* First Call setup */
+			if (SRF_IS_FIRSTCALL())
+			{
+				funcctx = SRF_FIRSTCALL_INIT();
+				srfstate = (PLySRFState *)
+					MemoryContextAllocZero(funcctx->multi_call_memory_ctx,
+										   sizeof(PLySRFState));
+				/* Immediately register cleanup callback */
+				srfstate->callback.func = plpython_srf_cleanup_callback;
+				srfstate->callback.arg = (void *) srfstate;
+				MemoryContextRegisterResetCallback(funcctx->multi_call_memory_ctx,
+												   &srfstate->callback);
+				funcctx->user_fctx = (void *) srfstate;
+			}
+			/* Every call setup */
+			funcctx = SRF_PERCALL_SETUP();
+			Assert(funcctx != NULL);
+			srfstate = (PLySRFState *) funcctx->user_fctx;
+		}
+
+		if (srfstate == NULL || srfstate->iter == NULL)
 		{
 			/*
-			 * Simple type returning function or first time for SETOF
-			 * function: actually execute the function.
+			 * Non-SETOF function or first time for SETOF function: build
+			 * args, then actually execute the function.
 			 */
 			plargs = PLy_function_build_args(fcinfo, proc);
 			plrv = PLy_procedure_call(proc, "args", plargs);
-			if (!proc->is_setof)
-			{
-				/*
-				 * SETOF function parameters will be deleted when last row is
-				 * returned
-				 */
-				PLy_function_delete_args(proc);
-			}
 			Assert(plrv != NULL);
 		}
+		else
+		{
+			/*
+			 * Second or later call for a SETOF function: restore arguments in
+			 * globals dict to what they were when we left off.  We must do
+			 * this in case multiple evaluations of the same SETOF function
+			 * are interleaved.  It's a bit annoying, since the iterator may
+			 * not look at the arguments at all, but we have no way to know
+			 * that.  Fortunately this isn't terribly expensive.
+			 */
+			if (srfstate->savedargs)
+				PLy_function_restore_args(proc, srfstate->savedargs);
+			srfstate->savedargs = NULL; /* deleted by restore_args */
+		}
 
 		/*
 		 * If it returns a set, call the iterator to get the next return item.
@@ -77,12 +127,11 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 		 */
 		if (proc->is_setof)
 		{
-			bool		has_error = false;
-			ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;
-
-			if (proc->setof == NULL)
+			if (srfstate->iter == NULL)
 			{
 				/* first time -- do checks and setup */
+				ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;
+
 				if (!rsi || !IsA(rsi, ReturnSetInfo) ||
 					(rsi->allowedModes & SFRM_ValuePerCall) == 0)
 				{
@@ -94,11 +143,12 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 				rsi->returnMode = SFRM_ValuePerCall;
 
 				/* Make iterator out of returned object */
-				proc->setof = PyObject_GetIter(plrv);
+				srfstate->iter = PyObject_GetIter(plrv);
+
 				Py_DECREF(plrv);
 				plrv = NULL;
 
-				if (proc->setof == NULL)
+				if (srfstate->iter == NULL)
 					ereport(ERROR,
 							(errcode(ERRCODE_DATATYPE_MISMATCH),
 							 errmsg("returned object cannot be iterated"),
@@ -106,35 +156,30 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 			}
 
 			/* Fetch next from iterator */
-			plrv = PyIter_Next(proc->setof);
-			if (plrv)
-				rsi->isDone = ExprMultipleResult;
-			else
-			{
-				rsi->isDone = ExprEndResult;
-				has_error = PyErr_Occurred() != NULL;
-			}
-
-			if (rsi->isDone == ExprEndResult)
+			plrv = PyIter_Next(srfstate->iter);
+			if (plrv == NULL)
 			{
 				/* Iterator is exhausted or error happened */
-				Py_DECREF(proc->setof);
-				proc->setof = NULL;
-
-				Py_XDECREF(plargs);
-				Py_XDECREF(plrv);
+				bool		has_error = (PyErr_Occurred() != NULL);
 
-				PLy_function_delete_args(proc);
+				Py_DECREF(srfstate->iter);
+				srfstate->iter = NULL;
 
 				if (has_error)
 					PLy_elog(ERROR, "error fetching next item from iterator");
 
-				/* Disconnect from the SPI manager before returning */
-				if (SPI_finish() != SPI_OK_FINISH)
-					elog(ERROR, "SPI_finish failed");
-
-				fcinfo->isnull = true;
-				return (Datum) NULL;
+				/* Pass a null through the data-returning steps below */
+				Py_INCREF(Py_None);
+				plrv = Py_None;
+			}
+			else
+			{
+				/*
+				 * This won't be last call, so save argument values.  We do
+				 * this again each time in case the iterator is changing those
+				 * values.
+				 */
+				srfstate->savedargs = PLy_function_save_args(proc);
 			}
 		}
 
@@ -170,7 +215,15 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 		else if (plrv == Py_None)
 		{
 			fcinfo->isnull = true;
-			if (proc->result.is_rowtype < 1)
+
+			/*
+			 * In a SETOF function, the iteration-ending null isn't a real
+			 * value; don't pass it through the input function, which might
+			 * complain.
+			 */
+			if (srfstate && srfstate->iter == NULL)
+				rv = (Datum) 0;
+			else if (proc->result.is_rowtype < 1)
 				rv = InputFunctionCall(&proc->result.out.d.typfunc,
 									   NULL,
 									   proc->result.out.d.typioparam,
@@ -205,16 +258,28 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 	}
 	PG_CATCH();
 	{
+		/* Pop old arguments from the stack if they were pushed above */
+		PLy_global_args_pop(proc);
+
 		Py_XDECREF(plargs);
 		Py_XDECREF(plrv);
 
 		/*
-		 * If there was an error the iterator might have not been exhausted
-		 * yet. Set it to NULL so the next invocation of the function will
-		 * start the iteration again.
+		 * If there was an error within a SRF, the iterator might not have
+		 * been exhausted yet.  Clear it so the next invocation of the
+		 * function will start the iteration again.  (This code is probably
+		 * unnecessary now; plpython_srf_cleanup_callback should take care of
+		 * cleanup.  But it doesn't hurt anything to do it here.)
 		 */
-		Py_XDECREF(proc->setof);
-		proc->setof = NULL;
+		if (srfstate)
+		{
+			Py_XDECREF(srfstate->iter);
+			srfstate->iter = NULL;
+			/* And drop any saved args; we won't need them */
+			if (srfstate->savedargs)
+				PLy_function_drop_args(srfstate->savedargs);
+			srfstate->savedargs = NULL;
+		}
 
 		PG_RE_THROW();
 	}
@@ -222,9 +287,27 @@ PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
 
 	error_context_stack = plerrcontext.previous;
 
+	/* Pop old arguments from the stack if they were pushed above */
+	PLy_global_args_pop(proc);
+
 	Py_XDECREF(plargs);
 	Py_DECREF(plrv);
 
+	if (srfstate)
+	{
+		/* We're in a SRF, exit appropriately */
+		if (srfstate->iter == NULL)
+		{
+			/* Iterator exhausted, so we're done */
+			SRF_RETURN_DONE(funcctx);
+		}
+		else if (fcinfo->isnull)
+			SRF_RETURN_NEXT_NULL(funcctx);
+		else
+			SRF_RETURN_NEXT(funcctx, rv);
+	}
+
+	/* Plain function, just return the Datum value (possibly null) */
 	return rv;
 }
 
@@ -431,17 +514,195 @@ PLy_function_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc)
 	return args;
 }
 
+/*
+ * Construct a PLySavedArgs struct representing the current values of the
+ * procedure's arguments in its globals dict.  This can be used to restore
+ * those values when exiting a recursive call level or returning control to a
+ * set-returning function.
+ *
+ * This would not be necessary except for an ancient decision to make args
+ * available via the proc's globals :-( ... but we're stuck with that now.
+ */
+static PLySavedArgs *
+PLy_function_save_args(PLyProcedure *proc)
+{
+	PLySavedArgs *result;
+
+	/* saved args are always allocated in procedure's context */
+	result = (PLySavedArgs *)
+		MemoryContextAllocZero(proc->mcxt,
+							   offsetof(PLySavedArgs, namedargs) +
+							   proc->nargs * sizeof(PyObject *));
+	result->nargs = proc->nargs;
+
+	/* Fetch the "args" list */
+	result->args = PyDict_GetItemString(proc->globals, "args");
+	Py_XINCREF(result->args);
+
+	/* Fetch all the named arguments */
+	if (proc->argnames)
+	{
+		int			i;
+
+		for (i = 0; i < result->nargs; i++)
+		{
+			if (proc->argnames[i])
+			{
+				result->namedargs[i] = PyDict_GetItemString(proc->globals,
+														  proc->argnames[i]);
+				Py_XINCREF(result->namedargs[i]);
+			}
+		}
+	}
+
+	return result;
+}
+
+/*
+ * Restore procedure's arguments from a PLySavedArgs struct,
+ * then free the struct.
+ */
 static void
-PLy_function_delete_args(PLyProcedure *proc)
+PLy_function_restore_args(PLyProcedure *proc, PLySavedArgs *savedargs)
+{
+	/* Restore named arguments into their slots in the globals dict */
+	if (proc->argnames)
+	{
+		int			i;
+
+		for (i = 0; i < savedargs->nargs; i++)
+		{
+			if (proc->argnames[i] && savedargs->namedargs[i])
+			{
+				PyDict_SetItemString(proc->globals, proc->argnames[i],
+									 savedargs->namedargs[i]);
+				Py_DECREF(savedargs->namedargs[i]);
+			}
+		}
+	}
+
+	/* Restore the "args" object, too */
+	if (savedargs->args)
+	{
+		PyDict_SetItemString(proc->globals, "args", savedargs->args);
+		Py_DECREF(savedargs->args);
+	}
+
+	/* And free the PLySavedArgs struct */
+	pfree(savedargs);
+}
+
+/*
+ * Free a PLySavedArgs struct without restoring the values.
+ */
+static void
+PLy_function_drop_args(PLySavedArgs *savedargs)
 {
 	int			i;
 
-	if (!proc->argnames)
-		return;
+	/* Drop references for named args */
+	for (i = 0; i < savedargs->nargs; i++)
+	{
+		Py_XDECREF(savedargs->namedargs[i]);
+	}
+
+	/* Drop ref to the "args" object, too */
+	Py_XDECREF(savedargs->args);
+
+	/* And free the PLySavedArgs struct */
+	pfree(savedargs);
+}
 
-	for (i = 0; i < proc->nargs; i++)
-		if (proc->argnames[i])
-			PyDict_DelItemString(proc->globals, proc->argnames[i]);
+/*
+ * Save away any existing arguments for the given procedure, so that we can
+ * install new values for a recursive call.  This should be invoked before
+ * doing PLy_function_build_args().
+ *
+ * NB: caller must ensure that PLy_global_args_pop gets invoked once, and
+ * only once, per successful completion of PLy_global_args_push.  Otherwise
+ * we'll end up out-of-sync between the actual call stack and the contents
+ * of proc->argstack.
+ */
+static void
+PLy_global_args_push(PLyProcedure *proc)
+{
+	/* We only need to push if we are already inside some active call */
+	if (proc->calldepth > 0)
+	{
+		PLySavedArgs *node;
+
+		/* Build a struct containing current argument values */
+		node = PLy_function_save_args(proc);
+
+		/*
+		 * Push the saved argument values into the procedure's stack.  Once we
+		 * modify either proc->argstack or proc->calldepth, we had better
+		 * return without the possibility of error.
+		 */
+		node->next = proc->argstack;
+		proc->argstack = node;
+	}
+	proc->calldepth++;
+}
+
+/*
+ * Pop old arguments when exiting a recursive call.
+ *
+ * Note: the idea here is to adjust the proc's callstack state before doing
+ * anything that could possibly fail.  In event of any error, we want the
+ * callstack to look like we've done the pop.  Leaking a bit of memory is
+ * tolerable.
+ */
+static void
+PLy_global_args_pop(PLyProcedure *proc)
+{
+	Assert(proc->calldepth > 0);
+	/* We only need to pop if we were already inside some active call */
+	if (proc->calldepth > 1)
+	{
+		PLySavedArgs *ptr = proc->argstack;
+
+		/* Pop the callstack */
+		Assert(ptr != NULL);
+		proc->argstack = ptr->next;
+		proc->calldepth--;
+
+		/* Restore argument values, then free ptr */
+		PLy_function_restore_args(proc, ptr);
+	}
+	else
+	{
+		/* Exiting call depth 1 */
+		Assert(proc->argstack == NULL);
+		proc->calldepth--;
+
+		/*
+		 * We used to delete the named arguments (but not "args") from the
+		 * proc's globals dict when exiting the outermost call level for a
+		 * function.  This seems rather pointless though: nothing can see the
+		 * dict until the function is called again, at which time we'll
+		 * overwrite those dict entries.  So don't bother with that.
+		 */
+	}
+}
+
+/*
+ * Memory context deletion callback for cleaning up a PLySRFState.
+ * We need this in case execution of the SRF is terminated early,
+ * due to error or the caller simply not running it to completion.
+ */
+static void
+plpython_srf_cleanup_callback(void *arg)
+{
+	PLySRFState *srfstate = (PLySRFState *) arg;
+
+	/* Release refcount on the iter, if we still have one */
+	Py_XDECREF(srfstate->iter);
+	srfstate->iter = NULL;
+	/* And drop any saved args; we won't need them */
+	if (srfstate->savedargs)
+		PLy_function_drop_args(srfstate->savedargs);
+	srfstate->savedargs = NULL;
 }
 
 static void
@@ -785,7 +1046,7 @@ plpython_trigger_error_callback(void *arg)
 
 /* execute Python code, propagate Python errors to the backend */
 static PyObject *
-PLy_procedure_call(PLyProcedure *proc, char *kargs, PyObject *vargs)
+PLy_procedure_call(PLyProcedure *proc, const char *kargs, PyObject *vargs)
 {
 	PyObject   *rv;
 	int volatile save_subxact_level = list_length(explicit_subtransactions);

src/pl/plpython/plpy_procedure.c

@@ -188,10 +188,11 @@ PLy_procedure_create(HeapTuple procTup, Oid fn_oid, bool is_trigger)
 		proc->pyname = pstrdup(procName);
 		proc->fn_xmin = HeapTupleHeaderGetRawXmin(procTup->t_data);
 		proc->fn_tid = procTup->t_self;
-		/* Remember if function is STABLE/IMMUTABLE */
-		proc->fn_readonly =
-			(procStruct->provolatile != PROVOLATILE_VOLATILE);
+		proc->fn_readonly = (procStruct->provolatile != PROVOLATILE_VOLATILE);
+		proc->is_setof = procStruct->proretset;
 		PLy_typeinfo_init(&proc->result, proc->mcxt);
+		proc->src = NULL;
+		proc->argnames = NULL;
 		for (i = 0; i < FUNC_MAX_ARGS; i++)
 			PLy_typeinfo_init(&proc->args[i], proc->mcxt);
 		proc->nargs = 0;
@@ -200,12 +201,11 @@ PLy_procedure_create(HeapTuple procTup, Oid fn_oid, bool is_trigger)
 											Anum_pg_proc_protrftypes,
 											&isnull);
 		proc->trftypes = isnull ? NIL : oid_array_to_list(protrftypes_datum);
-		proc->code = proc->statics = NULL;
+		proc->code = NULL;
+		proc->statics = NULL;
 		proc->globals = NULL;
-		proc->is_setof = procStruct->proretset;
-		proc->setof = NULL;
-		proc->src = NULL;
-		proc->argnames = NULL;
+		proc->calldepth = 0;
+		proc->argstack = NULL;
 
 		/*
 		 * get information required for output conversion of the return value,

src/pl/plpython/plpy_procedure.h

@@ -11,6 +11,15 @@
 extern void init_procedure_caches(void);
 
 
+/* saved arguments for outer recursion level or set-returning function */
+typedef struct PLySavedArgs
+{
+	struct PLySavedArgs *next;	/* linked-list pointer */
+	PyObject   *args;			/* "args" element of globals dict */
+	int			nargs;			/* length of namedargs array */
+	PyObject   *namedargs[FLEXIBLE_ARRAY_MEMBER];		/* named args */
+} PLySavedArgs;
+
 /* cached procedure data */
 typedef struct PLyProcedure
 {
@@ -21,10 +30,9 @@ typedef struct PLyProcedure
 	TransactionId fn_xmin;
 	ItemPointerData fn_tid;
 	bool		fn_readonly;
+	bool		is_setof;		/* true, if procedure returns result set */
 	PLyTypeInfo result;			/* also used to store info for trigger tuple
 								 * type */
-	bool		is_setof;		/* true, if procedure returns result set */
-	PyObject   *setof;			/* contents of result set. */
 	char	   *src;			/* textual procedure code, after mangling */
 	char	  **argnames;		/* Argument names */
 	PLyTypeInfo args[FUNC_MAX_ARGS];
@@ -34,6 +42,8 @@ typedef struct PLyProcedure
 	PyObject   *code;			/* compiled procedure code */
 	PyObject   *statics;		/* data saved across calls, local scope */
 	PyObject   *globals;		/* data saved across calls, global scope */
+	long		calldepth;		/* depth of recursive calls of function */
+	PLySavedArgs *argstack;		/* stack of outer-level call arguments */
 } PLyProcedure;
 
 /* the procedure cache key */

src/pl/plpython/sql/plpython_setof.sql

@@ -63,6 +63,18 @@ SELECT test_setof_as_iterator(2, null);
 
 SELECT test_setof_spi_in_iterator();
 
+-- set-returning function that modifies its parameters
+CREATE OR REPLACE FUNCTION ugly(x int, lim int) RETURNS SETOF int AS $$
+global x
+while x <= lim:
+    yield x
+    x = x + 1
+$$ LANGUAGE plpythonu;
+
+SELECT ugly(1, 5);
+
+-- interleaved execution of such a function
+SELECT ugly(1,3), ugly(7,8);
 
 -- returns set of named-composite-type tuples
 CREATE OR REPLACE FUNCTION get_user_records()

src/pl/plpython/sql/plpython_spi.sql

@@ -52,9 +52,6 @@ return None
 '
 	LANGUAGE plpythonu;
 
-
-
-
 CREATE FUNCTION join_sequences(s sequences) RETURNS text
 	AS
 'if not s["multipart"]:
@@ -68,10 +65,16 @@ return seq
 '
 	LANGUAGE plpythonu;
 
+CREATE FUNCTION spi_recursive_sum(a int) RETURNS int
+	AS
+'r = 0
+if a > 1:
+    r = plpy.execute("SELECT spi_recursive_sum(%d) as a" % (a-1))[0]["a"]
+return a + r
+'
+	LANGUAGE plpythonu;
 
-
-
-
+--
 -- spi and nested calls
 --
 select nested_call_one('pass this along');
@@ -79,15 +82,13 @@ select spi_prepared_plan_test_one('doe');
 select spi_prepared_plan_test_one('smith');
 select spi_prepared_plan_test_nested('smith');
 
-
-
-
 SELECT join_sequences(sequences) FROM sequences;
 SELECT join_sequences(sequences) FROM sequences
 	WHERE join_sequences(sequences) ~* '^A';
 SELECT join_sequences(sequences) FROM sequences
 	WHERE join_sequences(sequences) ~* '^B';
 
+SELECT spi_recursive_sum(10);
 
 --
 -- plan and result objects