add tests for MY_CXT API and improve its documentation

p4raw-id: //depot/perl@26522

1 files changed, 37 insertions, 1 deletions

diff --git a/pod/perlxs.pod b/pod/perlxs.pod
index 462f84ce3f..b3ba08f56a 100644
--- a/pod/perlxs.pod
+++ b/pod/perlxs.pod
@@ -1921,6 +1921,11 @@ Below is an example module that makes use of the macros.
         else
           RETVAL = newSVpv(MY_CXT.name[index - 1]);
 
+    void
+    CLONE(...)
+	CODE:
+	MY_CXT_CLONE;
+
 
 B<REFERENCE>
 
@@ -1956,7 +1961,10 @@ of C<my_cxt_t>.
 
 The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct.
 
-It I<must> be called exactly once -- typically in a BOOT: section.
+It I<must> be called exactly once -- typically in a BOOT: section. If you
+are maintaining multiple interpreters, it should be called once in each
+interpreter instance, except for interpreters cloned from existing ones.
+(But see C<MY_CXT_CLONE> below.)
 
 =item dMY_CXT
 
@@ -1977,6 +1985,34 @@ then use this to access the C<index> member
     dMY_CXT;
     MY_CXT.index = 2;
 
+=item aMY_CXT/pMY_CXT
+
+C<dMY_CXT> may be quite expensive to calculate, and to avoid the overhead
+of invoking it in each function it is possible to pass the declaration
+onto other functions using the C<aMY_CXT>/C<pMY_CXT> macros, eg
+
+    void sub1() {
+	dMY_CXT;
+	MY_CXT.index = 1;
+	sub2(aMY_CXT);
+    }
+
+    void sub2(pMY_CXT) {
+	MY_CXT.index = 2;
+    }
+
+Analogously to C<pTHX>, there are equivalent forms for when the macro is the
+first or last in multiple arguments, where an underscore represents a
+comma, i.e.  C<_aMY_CXT>, C<aMY_CXT_>, C<_pMY_CXT> and C<pMY_CXT_>.
+
+=item MY_CXT_CLONE
+
+By default, when a new interpreter is created as a copy of an existing one
+(eg via C<<threads->new()>>), both interpreters share the same physical
+my_cxt_t structure. Calling C<MY_CXT_CLONE> (typically via the package's
+C<CLONE()> function), causes a byte-for-byte copy of the structure to be
+taken, and any future dMY_CXT will cause the copy to be accessed instead.
+
 =back
 
 =head1 EXAMPLES