Add INJECTION_POINT_CACHED() to run injection points directly from cache

This new macro is able to perform a direct lookup from the local cache
of injection points (refreshed each time a point is loaded or run),
without touching the shared memory state of injection points at all.

This works in combination with INJECTION_POINT_LOAD(), and it is better
than INJECTION_POINT() in a critical section due to the fact that it
would avoid all memory allocations should a concurrent detach happen
since a LOAD(), as it retrieves a callback from the backend-private
memory.

The documentation is updated to describe in more details how to use this
new macro with a load.  Some tests are added to the module
injection_points based on a new SQL function that acts as a wrapper of
INJECTION_POINT_CACHED().

Based on a suggestion from Heikki Linnakangas.

Author: Heikki Linnakangas, Michael Paquier
Discussion: https://postgr.es/m/58d588d0-e63f-432f-9181-bed29313dece@iki.fi

4 files changed, 39 insertions, 0 deletions

diff --git a/src/test/modules/injection_points/expected/injection_points.out b/src/test/modules/injection_points/expected/injection_points.out
index 2f60da900bb..f25bbe4966e 100644
--- a/src/test/modules/injection_points/expected/injection_points.out
+++ b/src/test/modules/injection_points/expected/injection_points.out
@@ -129,6 +129,12 @@ SELECT injection_points_detach('TestInjectionLog2');
 (1 row)
 
 -- Loading
+SELECT injection_points_cached('TestInjectionLogLoad'); -- nothing in cache
+ injection_points_cached 
+-------------------------
+ 
+(1 row)
+
 SELECT injection_points_load('TestInjectionLogLoad'); -- nothing
  injection_points_load 
 -----------------------
@@ -147,6 +153,13 @@ SELECT injection_points_load('TestInjectionLogLoad'); -- nothing happens
  
 (1 row)
 
+SELECT injection_points_cached('TestInjectionLogLoad'); -- runs from cache
+NOTICE:  notice triggered for injection point TestInjectionLogLoad
+ injection_points_cached 
+-------------------------
+ 
+(1 row)
+
 SELECT injection_points_run('TestInjectionLogLoad'); -- runs from cache
 NOTICE:  notice triggered for injection point TestInjectionLogLoad
  injection_points_run 
diff --git a/src/test/modules/injection_points/injection_points--1.0.sql b/src/test/modules/injection_points/injection_points--1.0.sql
index e275c2cf5b6..0f280419a55 100644
--- a/src/test/modules/injection_points/injection_points--1.0.sql
+++ b/src/test/modules/injection_points/injection_points--1.0.sql
@@ -35,6 +35,16 @@ AS 'MODULE_PATHNAME', 'injection_points_run'
 LANGUAGE C STRICT PARALLEL UNSAFE;
 
 --
+-- injection_points_cached()
+--
+-- Executes the action attached to the injection point, from local cache.
+--
+CREATE FUNCTION injection_points_cached(IN point_name TEXT)
+RETURNS void
+AS 'MODULE_PATHNAME', 'injection_points_cached'
+LANGUAGE C STRICT PARALLEL UNSAFE;
+
+--
 -- injection_points_wakeup()
 --
 -- Wakes up a waiting injection point.
diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index b6c8e893246..15f9d0233c3 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -334,6 +334,20 @@ injection_points_run(PG_FUNCTION_ARGS)
 }
 
 /*
+ * SQL function for triggering an injection point from cache.
+ */
+PG_FUNCTION_INFO_V1(injection_points_cached);
+Datum
+injection_points_cached(PG_FUNCTION_ARGS)
+{
+	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	INJECTION_POINT_CACHED(name);
+
+	PG_RETURN_VOID();
+}
+
+/*
  * SQL function for waking up an injection point waiting in injection_wait().
  */
 PG_FUNCTION_INFO_V1(injection_points_wakeup);
diff --git a/src/test/modules/injection_points/sql/injection_points.sql b/src/test/modules/injection_points/sql/injection_points.sql
index fabf0a8823b..e3a481d6044 100644
--- a/src/test/modules/injection_points/sql/injection_points.sql
+++ b/src/test/modules/injection_points/sql/injection_points.sql
@@ -42,9 +42,11 @@ SELECT injection_points_run('TestInjectionLog2'); -- notice
 SELECT injection_points_detach('TestInjectionLog2');
 
 -- Loading
+SELECT injection_points_cached('TestInjectionLogLoad'); -- nothing in cache
 SELECT injection_points_load('TestInjectionLogLoad'); -- nothing
 SELECT injection_points_attach('TestInjectionLogLoad', 'notice');
 SELECT injection_points_load('TestInjectionLogLoad'); -- nothing happens
+SELECT injection_points_cached('TestInjectionLogLoad'); -- runs from cache
 SELECT injection_points_run('TestInjectionLogLoad'); -- runs from cache
 SELECT injection_points_detach('TestInjectionLogLoad');