Fix error handling in pltcl_returnnext.

We can't throw elog(ERROR) out of a Tcl command procedure; we have
to catch the error and return TCL_ERROR to the Tcl interpreter.
pltcl_returnnext failed to meet this requirement, so that errors
detected by pltcl_build_tuple_result or other functions called here
led to longjmp'ing out of the Tcl interpreter and thereby leaving it
in a bad state.  Use the existing subtransaction support to prevent
that.  Oversight in commit 26abb50c4, found more or less accidentally
by the buildfarm thanks to the tests added in 961bed020.

Report: https://postgr.es/m/30647.1483989734@sss.pgh.pa.us

diff --git a/src/pl/tcl/pltcl.c b/src/pl/tcl/pltcl.c
index d813dcb3a61b590276b193c6bb3107516c3fca2c..ec5b54ab324464e18ec672bd68b8a3a929c1bc48 100644 (file)
--- a/src/pl/tcl/pltcl.c
+++ b/src/pl/tcl/pltcl.c
@@ -299,6 +299,14 @@ static int pltcl_SPI_execute_plan(ClientData cdata, Tcl_Interp *interp,
 static int pltcl_SPI_lastoid(ClientData cdata, Tcl_Interp *interp,
                  int objc, Tcl_Obj *const objv[]);
 
+static void pltcl_subtrans_begin(MemoryContext oldcontext,
+                    ResourceOwner oldowner);
+static void pltcl_subtrans_commit(MemoryContext oldcontext,
+                     ResourceOwner oldowner);
+static void pltcl_subtrans_abort(Tcl_Interp *interp,
+                    MemoryContext oldcontext,
+                    ResourceOwner oldowner);
+
 static void pltcl_set_tuple_values(Tcl_Interp *interp, const char *arrayname,
                       uint64 tupno, HeapTuple tuple, TupleDesc tupdesc);
 static Tcl_Obj *pltcl_build_tuple_argument(HeapTuple tuple, TupleDesc tupdesc);
@@ -2073,9 +2081,9 @@ pltcl_returnnext(ClientData cdata, Tcl_Interp *interp,
    pltcl_call_state *call_state = pltcl_current_call_state;
    FunctionCallInfo fcinfo = call_state->fcinfo;
    pltcl_proc_desc *prodesc = call_state->prodesc;
-   int         result = TCL_OK;
-   MemoryContext tmpcxt;
-   MemoryContext oldcxt;
+   MemoryContext oldcontext = CurrentMemoryContext;
+   ResourceOwner oldowner = CurrentResourceOwner;
+   volatile int result = TCL_OK;
 
    /*
     * Check that we're called as a set-returning function
@@ -2103,52 +2111,63 @@ pltcl_returnnext(ClientData cdata, Tcl_Interp *interp,
        return TCL_ERROR;
    }
 
-   /* Set up tuple store if first output row */
-   if (call_state->tuple_store == NULL)
-       pltcl_init_tuple_store(call_state);
+   /*
+    * The rest might throw elog(ERROR), so must run in a subtransaction.
+    *
+    * A small advantage of using a subtransaction is that it provides a
+    * short-lived memory context for free, so we needn't worry about leaking
+    * memory here.  To use that context, call BeginInternalSubTransaction
+    * directly instead of going through pltcl_subtrans_begin.
+    */
+   BeginInternalSubTransaction(NULL);
+   PG_TRY();
+   {
+       /* Set up tuple store if first output row */
+       if (call_state->tuple_store == NULL)
+           pltcl_init_tuple_store(call_state);
 
-   /* Make short-lived context to run input functions in */
-   tmpcxt = AllocSetContextCreate(CurrentMemoryContext,
-                                  "pltcl_returnnext",
-                                  ALLOCSET_SMALL_SIZES);
-   oldcxt = MemoryContextSwitchTo(tmpcxt);
+       if (prodesc->fn_retistuple)
+       {
+           Tcl_Obj   **rowObjv;
+           int         rowObjc;
 
-   if (prodesc->fn_retistuple)
-   {
-       Tcl_Obj   **rowObjv;
-       int         rowObjc;
+           /* result should be a list, so break it down */
+           if (Tcl_ListObjGetElements(interp, objv[1], &rowObjc, &rowObjv) == TCL_ERROR)
+               result = TCL_ERROR;
+           else
+           {
+               HeapTuple   tuple;
 
-       /* result should be a list, so break it down */
-       if (Tcl_ListObjGetElements(interp, objv[1], &rowObjc, &rowObjv) == TCL_ERROR)
-           result = TCL_ERROR;
+               tuple = pltcl_build_tuple_result(interp, rowObjv, rowObjc,
+                                                call_state);
+               tuplestore_puttuple(call_state->tuple_store, tuple);
+           }
+       }
        else
        {
-           HeapTuple   tuple;
-
-           tuple = pltcl_build_tuple_result(interp, rowObjv, rowObjc,
-                                            call_state);
-           tuplestore_puttuple(call_state->tuple_store, tuple);
+           Datum       retval;
+           bool        isNull = false;
+
+           /* for paranoia's sake, check that tupdesc has exactly one column */
+           if (call_state->ret_tupdesc->natts != 1)
+               elog(ERROR, "wrong result type supplied in return_next");
+
+           retval = InputFunctionCall(&prodesc->result_in_func,
+                                   utf_u2e((char *) Tcl_GetString(objv[1])),
+                                      prodesc->result_typioparam,
+                                      -1);
+           tuplestore_putvalues(call_state->tuple_store, call_state->ret_tupdesc,
+                                &retval, &isNull);
        }
+
+       pltcl_subtrans_commit(oldcontext, oldowner);
    }
-   else
+   PG_CATCH();
    {
-       Datum       retval;
-       bool        isNull = false;
-
-       /* for paranoia's sake, check that tupdesc has exactly one column */
-       if (call_state->ret_tupdesc->natts != 1)
-           elog(ERROR, "wrong result type supplied in return_next");
-
-       retval = InputFunctionCall(&prodesc->result_in_func,
-                                  utf_u2e((char *) Tcl_GetString(objv[1])),
-                                  prodesc->result_typioparam,
-                                  -1);
-       tuplestore_putvalues(call_state->tuple_store, call_state->ret_tupdesc,
-                            &retval, &isNull);
+       pltcl_subtrans_abort(interp, oldcontext, oldowner);
+       return TCL_ERROR;
    }
-
-   MemoryContextSwitchTo(oldcxt);
-   MemoryContextDelete(tmpcxt);
+   PG_END_TRY();
 
    return result;
 }