Add support for runtime arguments in injection points

The macros INJECTION_POINT() and INJECTION_POINT_CACHED() are extended
with an optional argument that can be passed down to the callback
attached when an injection point is run, giving to callbacks the
possibility to manipulate a stack state given by the caller.  The
existing callbacks in modules injection_points and test_aio have their
declarations adjusted based on that.

da7226993fd4 (core AIO infrastructure) and 93bc3d75d8e1 (test_aio) and
been relying on a set of workarounds where a static variable called
pgaio_inj_cur_handle is used as runtime argument in the injection point
callbacks used by the AIO tests, in combination with a TRY/CATCH block
to reset the argument value.  The infrastructure introduced in this
commit will be reused for the AIO tests, simplifying them.

Reviewed-by: Greg Burd <greg@burd.me>
Discussion: https://postgr.es/m/Z_y9TtnXubvYAApS@paquier.xyz

1 files changed, 10 insertions, 6 deletions

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 3a73b02ccaf..2d81afce8cb 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -3829,15 +3829,17 @@ uint32 WaitEventExtensionNew(const char *wait_event_name)
      An injection point with a given <literal>name</literal> is declared using
      macro:
 <programlisting>
-INJECTION_POINT(name);
+INJECTION_POINT(name, arg);
 </programlisting>
 
      There are a few injection points already declared at strategic points
      within the server code. After adding a new injection point the code needs
      to be compiled in order for that injection point to be available in the
      binary. Add-ins written in C-language can declare injection points in
-     their own code using the same macro. The injection point names should
-     use lower-case characters, with terms separated by dashes.
+     their own code using the same macro. The injection point names should use
+     lower-case characters, with terms separated by
+     dashes. <literal>arg</literal> is an optional argument value given to the
+     callback at run-time.
     </para>
 
     <para>
@@ -3847,7 +3849,7 @@ INJECTION_POINT(name);
      a two-step approach with the following macros:
 <programlisting>
 INJECTION_POINT_LOAD(name);
-INJECTION_POINT_CACHED(name);
+INJECTION_POINT_CACHED(name, arg);
 </programlisting>
 
      Before entering the critical section,
@@ -3880,7 +3882,9 @@ extern void InjectionPointAttach(const char *name,
      <literal>InjectionPointCallback</literal>:
 <programlisting>
 static void
-custom_injection_callback(const char *name, const void *private_data)
+custom_injection_callback(const char *name,
+                          const void *private_data,
+                          void *arg)
 {
     uint32 wait_event_info = WaitEventInjectionPointNew(name);
 
@@ -3909,7 +3913,7 @@ if (IS_INJECTION_POINT_ATTACHED("before-foobar"))
     local_var = 123;
 
     /* also execute the callback */
-    INJECTION_POINT_CACHED("before-foobar");
+    INJECTION_POINT_CACHED("before-foobar", NULL);
 }
 #endif
 </programlisting>