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

1 files changed, 17 insertions, 0 deletions

diff --git a/src/backend/utils/misc/injection_point.c b/src/backend/utils/misc/injection_point.c
index 84ad5e470d7..8ad0c27bc8a 100644
--- a/src/backend/utils/misc/injection_point.c
+++ b/src/backend/utils/misc/injection_point.c
@@ -553,3 +553,20 @@ InjectionPointRun(const char *name)
 	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 = injection_point_cache_get(name);
+	if (cache_entry)
+		cache_entry->callback(name, cache_entry->private_data);
+#else
+	elog(ERROR, "Injection points are not supported by this build");
+#endif
+}