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, 18 insertions, 0 deletions

diff --git a/src/pl/plperl/expected/plperl.out b/src/pl/plperl/expected/plperl.out
index 906dc15e0ca..29c1d11c447 100644
--- a/src/pl/plperl/expected/plperl.out
+++ b/src/pl/plperl/expected/plperl.out
@@ -693,3 +693,21 @@ $$ LANGUAGE plperl;
 SELECT text_scalarref();
 ERROR:  PL/Perl function must return reference to hash or array
 CONTEXT:  PL/Perl function "text_scalarref"
+-- check safe behavior when a function body is replaced during execution
+CREATE OR REPLACE FUNCTION self_modify(INTEGER) RETURNS INTEGER AS $$
+   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);
+ self_modify 
+-------------
+          84
+(1 row)
+
+SELECT self_modify(42);
+ self_modify 
+-------------
+         126
+(1 row)
+