Make plperl safe against functions that are redefined while running.

validate_plperl_function() supposed that it could free an old
plperl_proc_desc struct immediately upon detecting that it was stale.
However, if a plperl function is called recursively, this could result
in deleting the struct out from under an outer invocation, leading to
misbehavior or crashes.  Add a simple reference-count mechanism to
ensure that such structs are freed only when the last reference goes
away.

Per investigation of bug #7516 from Marko Tiikkaja.  I am not certain
that this error explains his report, because he says he didn't have
any recursive calls --- but it's hard to see how else it could have
crashed right there.  In any case, this definitely fixes some problems
in the area.

Back-patch to all active branches.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/pl/plperl/sql/plperl.sql b/src/pl/plperl/sql/plperl.sql
index a5e3840dac2..ad361614c48 100644
--- a/src/pl/plperl/sql/plperl.sql
+++ b/src/pl/plperl/sql/plperl.sql
@@ -462,3 +462,13 @@ CREATE OR REPLACE FUNCTION text_scalarref() RETURNS text AS $$
 $$ LANGUAGE plperl;
 
 SELECT text_scalarref();
+
+-- check safe behavior when a function body is replaced during execution
+CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETURNS INTEGER AS $$
+   spi_exec_query('CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETURNS INTEGER AS \'return $_[0] * 3;\' LANGUAGE plperl;');
+   spi_exec_query('select self_modify(42) AS a');
+   return $_[0] * 2;
+$$ LANGUAGE plperl;
+
+SELECT self_modify(42);
+SELECT self_modify(42);