From dcb2da03245977d3524545740fce3750e046b1fc Mon Sep 17 00:00:00 2001
From: Rob Schaber <robschaber@gmail.com>
Date: Fri, 23 Jun 2017 16:52:19 -0500
Subject: [PATCH 1/3] Allow an inner handle to be hot-swapped from inside a
 callback.

---
 DBI.xs          | 27 ++++++++++++++++++++++++++-
 t/70callbacks.t | 22 ++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/DBI.xs b/DBI.xs
index ae44d97e..e3230736 100644
--- a/DBI.xs
+++ b/DBI.xs
@@ -3594,6 +3594,13 @@ XS(XS_DBI_dispatch)
 # endif
         DEFSV_set(temp_defsv);
 
+        /* We probably localized a member of imp_xxh earlier (call_depth) so
+         * we need to keep a reference to its inner handle owner until the
+         * end of scope so that it can be restored if our callback swaps out
+         * the handle and tries to garbage collect it.
+         */
+        sv_2mortal(newRV_inc(h));
+
         EXTEND(SP, items+1);
         PUSHMARK(SP);
         PUSHs(orig_h);                  /* push outer handle, then others params */
@@ -3604,6 +3611,24 @@ XS(XS_DBI_dispatch)
         outitems = call_sv(code, G_ARRAY); /* call the callback code */
         MSPAGAIN;
 
+        /* Callback may have swapped out the inner handle from underneath us.
+         * If so, we need to refresh our vars (h, mg, imp_xxh) before dispatch.
+         */
+        {
+            MAGIC *outer_magic = SvMAGIC(SvRV(orig_h));
+            if (outer_magic->mg_type != 'P')
+                outer_magic = mg_find(SvRV(h), 'P');
+            if (outer_magic != mg) {
+                SV    *inner_handle = outer_magic->mg_obj;
+                MAGIC *inner_magic  = SvMAGIC(SvRV(inner_handle));
+                if (inner_magic->mg_type != DBI_MAGIC)
+                    inner_magic = mg_find(SvRV(inner_handle), DBI_MAGIC);
+                mg = outer_magic;
+                h  = ST(0) = inner_handle;
+                imp_xxh = (imp_xxh_t *)inner_magic->mg_ptr;
+            }
+        }
+
         /* The callback code can undef $_ to indicate to skip dispatch */
         skip_dispatch = !SvOK(DEFSV);
         /* put $_ back now, but with an incremented ref count to compensate
@@ -5135,7 +5160,7 @@ take_imp_data(h)
                 PUSHMARK(sp);
                 XPUSHs(*hp);
                 PUTBACK;
-                call_method("finish", G_VOID);
+                call_method("finish", G_VOID|G_DISCARD);
                 SPAGAIN;
                 PUTBACK;
                 sv_unmagic(SvRV(*hp), 'P'); /* untie */
diff --git a/t/70callbacks.t b/t/70callbacks.t
index 40903f98..f64ae03c 100644
--- a/t/70callbacks.t
+++ b/t/70callbacks.t
@@ -232,6 +232,28 @@ my $stress_sth = $stress_dbh->prepare("select 1");
 $stress_sth->{Callbacks}{execute} = sub { return; };
 $stress_sth->execute(@params);
 
+# Test that a db handle can be swapped out for a newly-created
+# one from inside a callback with no ill effects.
+{
+    my $dbh = DBI->connect($dsn);
+    my $old = tied %$dbh;
+    my $cb  = sub {
+        my ($dbh) = @_;
+        my $new_dbh = DBI->connect($dsn);
+        $dbh->swap_inner_handle($new_dbh);
+        return;
+    };
+    $dbh->{Callbacks} = { ping => $cb };
+    no warnings qw/once redefine/;
+    local *DBD::ExampleP::db::ping = sub {
+        my ($dbh) = @_;
+        my $new = tied %$dbh;
+        isnt $old, $new, 'inner handle replaced inside method';
+    };
+    $dbh->ping();
+    my $new = tied %$dbh;
+    isnt $old, $new, 'inner handle replaced after method';
+}
 
 done_testing();
 

From a06b7852c28f26bc2f427838937f346b6e4da1a2 Mon Sep 17 00:00:00 2001
From: Rob Schaber <robschaber@gmail.com>
Date: Fri, 23 Jun 2017 18:06:33 -0500
Subject: [PATCH 2/3] Fix improper test comparison in t/70callbacks.t

A dispatched method receives the inner handle, not outer.
---
 t/70callbacks.t | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/t/70callbacks.t b/t/70callbacks.t
index f64ae03c..d67622af 100644
--- a/t/70callbacks.t
+++ b/t/70callbacks.t
@@ -246,8 +246,7 @@ $stress_sth->execute(@params);
     $dbh->{Callbacks} = { ping => $cb };
     no warnings qw/once redefine/;
     local *DBD::ExampleP::db::ping = sub {
-        my ($dbh) = @_;
-        my $new = tied %$dbh;
+        my ($new) = @_;
         isnt $old, $new, 'inner handle replaced inside method';
     };
     $dbh->ping();

From c14b45aecb6daef4720d292faacdf203d2ef5279 Mon Sep 17 00:00:00 2001
From: Rob Schaber <robschaber@gmail.com>
Date: Fri, 23 Jun 2017 18:34:57 -0500
Subject: [PATCH 3/3] Get outer handle magic from the outer handle, not inner
 handle

During development, forgot to fix the secondary lookup after fixing
the primary one.
---
 DBI.xs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/DBI.xs b/DBI.xs
index e3230736..be2e0c09 100644
--- a/DBI.xs
+++ b/DBI.xs
@@ -3617,7 +3617,7 @@ XS(XS_DBI_dispatch)
         {
             MAGIC *outer_magic = SvMAGIC(SvRV(orig_h));
             if (outer_magic->mg_type != 'P')
-                outer_magic = mg_find(SvRV(h), 'P');
+                outer_magic = mg_find(SvRV(orig_h), 'P');
             if (outer_magic != mg) {
                 SV    *inner_handle = outer_magic->mg_obj;
                 MAGIC *inner_magic  = SvMAGIC(SvRV(inner_handle));