Support loading of injection points

This can be used to load an injection point and prewarm the
backend-level cache before running it, to avoid issues if the point
cannot be loaded due to restrictions in the code path where it would be
run, like a critical section where no memory allocation can happen
(load_external_function() can do allocations when expanding a library
name).

Tests can use a macro called INJECTION_POINT_LOAD() to load an injection
point.  The test module injection_points gains some tests, and a SQL
function able to load an injection point.

Based on a request from Andrey Borodin, who has implemented a test for
multixacts requiring this facility.

Reviewed-by: Andrey Borodin
Discussion: https://postgr.es/m/ZkrBE1e2q2wGvsoN@paquier.xyz

4 files changed, 66 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 dd9db06e10b..2f60da900bb 100644
--- a/src/test/modules/injection_points/expected/injection_points.out
+++ b/src/test/modules/injection_points/expected/injection_points.out
@@ -128,6 +128,38 @@ SELECT injection_points_detach('TestInjectionLog2');
  
 (1 row)
 
+-- Loading
+SELECT injection_points_load('TestInjectionLogLoad'); -- nothing
+ injection_points_load 
+-----------------------
+ 
+(1 row)
+
+SELECT injection_points_attach('TestInjectionLogLoad', 'notice');
+ injection_points_attach 
+-------------------------
+ 
+(1 row)
+
+SELECT injection_points_load('TestInjectionLogLoad'); -- nothing happens
+ injection_points_load 
+-----------------------
+ 
+(1 row)
+
+SELECT injection_points_run('TestInjectionLogLoad'); -- runs from cache
+NOTICE:  notice triggered for injection point TestInjectionLogLoad
+ injection_points_run 
+----------------------
+ 
+(1 row)
+
+SELECT injection_points_detach('TestInjectionLogLoad');
+ injection_points_detach 
+-------------------------
+ 
+(1 row)
+
 -- Runtime conditions
 SELECT injection_points_attach('TestConditionError', 'error');
  injection_points_attach 
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 c16a33b08db..e275c2cf5b6 100644
--- a/src/test/modules/injection_points/injection_points--1.0.sql
+++ b/src/test/modules/injection_points/injection_points--1.0.sql
@@ -15,6 +15,16 @@ AS 'MODULE_PATHNAME', 'injection_points_attach'
 LANGUAGE C STRICT PARALLEL UNSAFE;
 
 --
+-- injection_points_load()
+--
+-- Load an injection point already attached.
+--
+CREATE FUNCTION injection_points_load(IN point_name TEXT)
+RETURNS void
+AS 'MODULE_PATHNAME', 'injection_points_load'
+LANGUAGE C STRICT PARALLEL UNSAFE;
+
+--
 -- injection_points_run()
 --
 -- Executes the action attached to the injection point.
diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index 1b695a18203..b6c8e893246 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -303,6 +303,23 @@ injection_points_attach(PG_FUNCTION_ARGS)
 }
 
 /*
+ * SQL function for loading an injection point.
+ */
+PG_FUNCTION_INFO_V1(injection_points_load);
+Datum
+injection_points_load(PG_FUNCTION_ARGS)
+{
+	char	   *name = text_to_cstring(PG_GETARG_TEXT_PP(0));
+
+	if (inj_state == NULL)
+		injection_init_shmem();
+
+	INJECTION_POINT_LOAD(name);
+
+	PG_RETURN_VOID();
+}
+
+/*
  * SQL function for triggering an injection point.
  */
 PG_FUNCTION_INFO_V1(injection_points_run);
diff --git a/src/test/modules/injection_points/sql/injection_points.sql b/src/test/modules/injection_points/sql/injection_points.sql
index 71e2972a7e4..fabf0a8823b 100644
--- a/src/test/modules/injection_points/sql/injection_points.sql
+++ b/src/test/modules/injection_points/sql/injection_points.sql
@@ -41,6 +41,13 @@ SELECT injection_points_detach('TestInjectionLog'); -- fails
 SELECT injection_points_run('TestInjectionLog2'); -- notice
 SELECT injection_points_detach('TestInjectionLog2');
 
+-- Loading
+SELECT injection_points_load('TestInjectionLogLoad'); -- nothing
+SELECT injection_points_attach('TestInjectionLogLoad', 'notice');
+SELECT injection_points_load('TestInjectionLogLoad'); -- nothing happens
+SELECT injection_points_run('TestInjectionLogLoad'); -- runs from cache
+SELECT injection_points_detach('TestInjectionLogLoad');
+
 -- Runtime conditions
 SELECT injection_points_attach('TestConditionError', 'error');
 -- Any follow-up injection point attached will be local to this process.