Add LWLock for OSM usage in loader

Modify the loader to add a LWLock for OSM code.
Update the loader API version to 4.

.unreleased/pr_6608

@@ -0,0 +1 @@
+Implements: #6608 Add LWLock for OSM usage in loader

src/bgw/launcher_interface.c

@@ -11,7 +11,7 @@
 #include "launcher_interface.h"
 #include "compat/compat.h"
 
-#define MIN_LOADER_API_VERSION 3
+#define MIN_LOADER_API_VERSION 4
 
 extern bool
 ts_bgw_worker_reserve(void)

src/loader/bgw_interface.c

@@ -16,7 +16,14 @@
 
 /* This is where versioned-extension facing functions live. They shouldn't live anywhere else. */
 
-const int32 ts_bgw_loader_api_version = 3;
+/* All loader changes should always be backward compatible.
+ * Update ts_bgw_loader_api_version if the loader changes are needed for newer extension updates.
+ * e.g. adding a LWLock to loader is required for some future change coming to OSM extension version
+ * xxxx. RENDEZVOUS_BGW_LOADER_API_VERSION is used to verify if the loader in use is compatible with
+ * the current TimescaleDB version. This check happens in bgw/bgw_launcher.c When
+ * ts_bgw_loader_api_version is updated, check the compatibility in bgw/bgw_launcher.c as well
+ */
+const int32 ts_bgw_loader_api_version = 4;
 
 TS_FUNCTION_INFO_V1(ts_bgw_worker_reserve);
 TS_FUNCTION_INFO_V1(ts_bgw_worker_release);

src/loader/lwlocks.c

@@ -14,6 +14,7 @@
 
 #define TS_LWLOCKS_SHMEM_NAME "ts_lwlocks_shmem"
 #define CHUNK_APPEND_LWLOCK_TRANCHE_NAME "ts_chunk_append_lwlock_tranche"
+#define OSM_PARALLEL_LWLOCK_TRANCHE_NAME "ts_osm_parallel_lwlock_tranche"
 
 /*
  * since shared memory can only be setup in a library loaded as
@@ -22,6 +23,7 @@
 typedef struct TSLWLocks
 {
 	LWLock *chunk_append;
+	LWLock *osm_parallel_lwlock;
 } TSLWLocks;
 
 static TSLWLocks *ts_lwlocks = NULL;
@@ -30,7 +32,7 @@ void
 ts_lwlocks_shmem_startup()
 {
 	bool found;
-	LWLock **lock_pointer;
+	LWLock **lock_pointer, **osm_lock_pointer;
 
 	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
 	ts_lwlocks = ShmemInitStruct(TS_LWLOCKS_SHMEM_NAME, sizeof(TSLWLocks), &found);
@@ -38,6 +40,8 @@ ts_lwlocks_shmem_startup()
 	{
 		memset(ts_lwlocks, 0, sizeof(TSLWLocks));
 		ts_lwlocks->chunk_append = &(GetNamedLWLockTranche(CHUNK_APPEND_LWLOCK_TRANCHE_NAME))->lock;
+		ts_lwlocks->osm_parallel_lwlock =
+			&(GetNamedLWLockTranche(OSM_PARALLEL_LWLOCK_TRANCHE_NAME))->lock;
 	}
 	LWLockRelease(AddinShmemInitLock);
 
@@ -48,11 +52,21 @@ ts_lwlocks_shmem_startup()
 	 */
 	lock_pointer = (LWLock **) find_rendezvous_variable(RENDEZVOUS_CHUNK_APPEND_LWLOCK);
 	*lock_pointer = ts_lwlocks->chunk_append;
+	osm_lock_pointer = (LWLock **) find_rendezvous_variable(RENDEZVOUS_OSM_PARALLEL_LWLOCK);
+	*osm_lock_pointer = ts_lwlocks->osm_parallel_lwlock;
 }
 
+/*
+ * from postgres code comments:
+ * Extensions (or core code) can obtain an LWLocks by calling
+ * RequestNamedLWLockTranche() during postmaster startup.  Subsequently,
+ * call GetNamedLWLockTranche() to obtain a pointer to an array containing
+ * the number of LWLocks requested.
+ */
 void
 ts_lwlocks_shmem_alloc()
 {
 	RequestNamedLWLockTranche(CHUNK_APPEND_LWLOCK_TRANCHE_NAME, 1);
+	RequestNamedLWLockTranche(OSM_PARALLEL_LWLOCK_TRANCHE_NAME, 1);
 	RequestAddinShmemSpace(sizeof(TSLWLocks));
 }

src/loader/lwlocks.h

@@ -6,6 +6,7 @@
 #pragma once
 
 #define RENDEZVOUS_CHUNK_APPEND_LWLOCK "ts_chunk_append_lwlock"
+#define RENDEZVOUS_OSM_PARALLEL_LWLOCK "ts_osm_parallel_lwlock"
 
 void ts_lwlocks_shmem_startup(void);
 void ts_lwlocks_shmem_alloc(void);

test/expected/loader-tsl.out

@@ -557,6 +557,7 @@ CREATE EXTENSION timescaledb_osm VERSION 'mock-1';
 WARNING:  mock post_analyze_hook "mock-2"
 WARNING:  mock post_analyze_hook "mock-2"
 WARNING:  OSM-mock-1 _PG_init
+WARNING:  got lwlock osm lock
 WARNING:  mock post_analyze_hook "mock-2"
 WARNING:  mock post_analyze_hook "mock-2"
 -- Test that OSM process utility hook works:  it should see this DROP TABLE.

test/src/loader/osm_init.c

@@ -10,6 +10,7 @@
 
 #include "compat/compat.h"
 #include "export.h"
+#include "loader/lwlocks.h"
 
 #ifdef PG_MODULE_MAGIC
 PG_MODULE_MAGIC;
@@ -33,6 +34,16 @@ void
 _PG_init(void)
 {
 	elog(WARNING, "OSM-%s _PG_init", OSM_VERSION_MOD);
+	void *osm_lock_pointer = (LWLock **) find_rendezvous_variable(RENDEZVOUS_OSM_PARALLEL_LWLOCK);
+	if (osm_lock_pointer != NULL)
+	{
+		elog(WARNING, "got lwlock osm lock");
+	}
+	else
+	{
+		elog(WARNING, "NO lwlock osm lock");
+	}
+
 	prev_ProcessUtility_hook = ProcessUtility_hook;
 	ProcessUtility_hook = osm_process_utility_hook;
 }