0001-Add-INJECTION_POINT_CACHED.patch

From e33ab4202cf5e6ee79eef1927978d45e1cfa6034 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Tue, 16 Jul 2024 13:07:58 +0900
Subject: [PATCH] Add INJECTION_POINT_CACHED()

This works in combination with INJECTION_POINT_LOAD(), ensuring that an
injection point can be run without touching the shared memory area
related to injection points.
---
 src/include/utils/injection_point.h           |  3 ++
 src/backend/utils/misc/injection_point.c      | 33 ++++++++++++++++---
 .../expected/injection_points.out             | 13 ++++++++
 .../injection_points--1.0.sql                 | 10 ++++++
 .../injection_points/injection_points.c       | 14 ++++++++
 .../injection_points/sql/injection_points.sql |  2 ++
 doc/src/sgml/xfunc.sgml                       |  6 +++-
 7 files changed, 76 insertions(+), 5 deletions(-)

diff --git a/src/include/utils/injection_point.h b/src/include/utils/injection_point.h
index bd3a62425c..a385e3df64 100644
--- a/src/include/utils/injection_point.h
+++ b/src/include/utils/injection_point.h
@@ -17,9 +17,11 @@
 #ifdef USE_INJECTION_POINTS
 #define INJECTION_POINT_LOAD(name) InjectionPointLoad(name)
 #define INJECTION_POINT(name) InjectionPointRun(name)
+#define INJECTION_POINT_CACHED(name) InjectionPointCached(name)
 #else
 #define INJECTION_POINT_LOAD(name) ((void) name)
 #define INJECTION_POINT(name) ((void) name)
+#define INJECTION_POINT_CACHED(name) ((void) name)
 #endif
 
 /*
@@ -38,6 +40,7 @@ extern void InjectionPointAttach(const char *name,
 								 int private_data_size);
 extern void InjectionPointLoad(const char *name);
 extern void InjectionPointRun(const char *name);
+extern void InjectionPointCached(const char *name);
 extern bool InjectionPointDetach(const char *name);
 
 #endif							/* INJECTION_POINT_H */
diff --git a/src/backend/utils/misc/injection_point.c b/src/backend/utils/misc/injection_point.c
index 84ad5e470d..9dd6575a9a 100644
--- a/src/backend/utils/misc/injection_point.c
+++ b/src/backend/utils/misc/injection_point.c
@@ -415,10 +415,11 @@ InjectionPointDetach(const char *name)
  * Common workhorse of InjectionPointRun() and InjectionPointLoad()
  *
  * Checks if an injection point exists in shared memory, and update
- * the local cache entry accordingly.
+ * the local cache entry accordingly.  If "direct" is true, return the
+ * point after looking up for it only in the cache.
  */
 static InjectionPointCacheEntry *
-InjectionPointCacheRefresh(const char *name)
+InjectionPointCacheRefresh(const char *name, bool direct)
 {
 	uint32		max_inuse;
 	int			namelen;
@@ -461,6 +462,13 @@ InjectionPointCacheRefresh(const char *name)
 		cached = NULL;
 	}
 
+	/*
+	 * If using a direct lookup, forget about the shared memory array
+	 * and return immediately with the data found in the cache.
+	 */
+	if (direct)
+		return cached;
+
 	/*
 	 * Search the shared memory array.
 	 *
@@ -531,7 +539,7 @@ void
 InjectionPointLoad(const char *name)
 {
 #ifdef USE_INJECTION_POINTS
-	InjectionPointCacheRefresh(name);
+	InjectionPointCacheRefresh(name, false);
 #else
 	elog(ERROR, "Injection points are not supported by this build");
 #endif
@@ -546,7 +554,24 @@ InjectionPointRun(const char *name)
 #ifdef USE_INJECTION_POINTS
 	InjectionPointCacheEntry *cache_entry;
 
-	cache_entry = InjectionPointCacheRefresh(name);
+	cache_entry = InjectionPointCacheRefresh(name, false);
+	if (cache_entry)
+		cache_entry->callback(name, cache_entry->private_data);
+#else
+	elog(ERROR, "Injection points are not supported by this build");
+#endif
+}
+
+/*
+ * Execute an injection point directly from the cache, if defined.
+ */
+void
+InjectionPointCached(const char *name)
+{
+#ifdef USE_INJECTION_POINTS
+	InjectionPointCacheEntry *cache_entry;
+
+	cache_entry = InjectionPointCacheRefresh(name, true);
 	if (cache_entry)
 		cache_entry->callback(name, cache_entry->private_data);
 #else
diff --git a/src/test/modules/injection_points/expected/injection_points.out b/src/test/modules/injection_points/expected/injection_points.out
index 2f60da900b..f25bbe4966 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 e275c2cf5b..0f280419a5 100644
--- a/src/test/modules/injection_points/injection_points--1.0.sql
+++ b/src/test/modules/injection_points/injection_points--1.0.sql
@@ -34,6 +34,16 @@ RETURNS void
 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()
 --
diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index b6c8e89324..15f9d0233c 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -333,6 +333,20 @@ injection_points_run(PG_FUNCTION_ARGS)
 	PG_RETURN_VOID();
 }
 
+/*
+ * 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().
  */
diff --git a/src/test/modules/injection_points/sql/injection_points.sql b/src/test/modules/injection_points/sql/injection_points.sql
index fabf0a8823..e3a481d604 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');
 
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 756a9d07fb..f02a48ead4 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -3629,7 +3629,11 @@ INJECTION_POINT_LOAD(name);
      doing all memory allocations at this stage without running the callback.
      This is useful when an injection point is attached in a critical section
      where no memory can be allocated: load the injection point outside the
-     critical section, then run it in the critical section.
+     critical section, then run it in the critical section directly from
+     the process cache:
+<programlisting>
+INJECTION_POINT_CACHED(name);
+</programlisting>
     </para>
 
     <para>
-- 
2.45.2