Allow passing a pointer to GetNamedDSMSegment()'s init callback.

nathan-bossart · nathan-bossart · commit 48d4a1423d2e · 2025-12-15T14:27:16.000-06:00
This commit adds a new "void *arg" parameter to GetNamedDSMSegment() that is passed to the initialization callback function. This is useful for reusing an initialization callback function for multiple DSM segments. Author: Zsolt Parragi <zsolt.parragi@percona.com> Reviewed-by: Sami Imseih <samimseih@gmail.com> Discussion: https://postgr.es/m/CAN4CZFMjh8TrT9ZhWgjVTzBDkYZi2a84BnZ8bM%2BfLPuq7Cirzg%40mail.gmail.com
diff --git a/contrib/pg_prewarm/autoprewarm.c b/contrib/pg_prewarm/autoprewarm.c
@@ -858,7 +858,7 @@ autoprewarm_dump_now(PG_FUNCTION_ARGS)
 }
 
 static void
-apw_init_state(void *ptr)
+apw_init_state(void *ptr, void *arg)
 {
 	AutoPrewarmSharedState *state = (AutoPrewarmSharedState *) ptr;
 
@@ -880,7 +880,7 @@ apw_init_shmem(void)
 	apw_state = GetNamedDSMSegment("autoprewarm",
 								   sizeof(AutoPrewarmSharedState),
 								   apw_init_state,
-								   &found);
+								   &found, NULL);
 
 	return found;
 }
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
@@ -3696,15 +3696,18 @@ LWLockRelease(AddinShmemInitLock);
       use the shared memory should obtain a pointer to it by calling:
 <programlisting>
 void *GetNamedDSMSegment(const char *name, size_t size,
-                         void (*init_callback) (void *ptr),
-                         bool *found)
+                         void (*init_callback) (void *ptr, void *arg),
+                         bool *found, void *arg)
 </programlisting>
       If a dynamic shared memory segment with the given name does not yet
       exist, this function will allocate it and initialize it with the provided
       <function>init_callback</function> callback function.  If the segment has
       already been allocated and initialized by another backend, this function
       simply attaches the existing dynamic shared memory segment to the current
-      backend.
+      backend.  In the former case, <function>GetNamedDSMSegment</function>
+      passes the <literal>void *arg</literal> argument to the
+      <function>init_callback</function>.  This is particularly useful for
+      reusing an initialization callback function for multiple DSM segments.
      </para>
 
      <para>
diff --git a/src/backend/storage/ipc/dsm_registry.c b/src/backend/storage/ipc/dsm_registry.c
@@ -180,11 +180,13 @@ init_dsm_registry(void)
  * Initialize or attach a named DSM segment.
  *
  * This routine returns the address of the segment.  init_callback is called to
- * initialize the segment when it is first created.
+ * initialize the segment when it is first created.  'arg' is passed through to
+ * the initialization callback function.
  */
 void *
 GetNamedDSMSegment(const char *name, size_t size,
-				   void (*init_callback) (void *ptr), bool *found)
+				   void (*init_callback) (void *ptr, void *arg),
+				   bool *found, void *arg)
 {
 	DSMRegistryEntry *entry;
 	MemoryContext oldcontext;
@@ -235,7 +237,7 @@ GetNamedDSMSegment(const char *name, size_t size,
 		seg = dsm_create(size, 0);
 
 		if (init_callback)
-			(*init_callback) (dsm_segment_address(seg));
+			(*init_callback) (dsm_segment_address(seg), arg);
 
 		dsm_pin_segment(seg);
 		dsm_pin_mapping(seg);
diff --git a/src/include/storage/dsm_registry.h b/src/include/storage/dsm_registry.h
@@ -16,8 +16,8 @@
 #include "lib/dshash.h"
 
 extern void *GetNamedDSMSegment(const char *name, size_t size,
-								void (*init_callback) (void *ptr),
-								bool *found);
+								void (*init_callback) (void *ptr, void *arg),
+								bool *found, void *arg);
 extern dsa_area *GetNamedDSA(const char *name, bool *found);
 extern dshash_table *GetNamedDSHash(const char *name,
 									const dshash_parameters *params,
diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
@@ -115,7 +115,7 @@ static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
  * when initializing dynamically with a DSM or when loading the module.
  */
 static void
-injection_point_init_state(void *ptr)
+injection_point_init_state(void *ptr, void *arg)
 {
 	InjectionPointSharedState *state = (InjectionPointSharedState *) ptr;
 
@@ -159,7 +159,7 @@ injection_shmem_startup(void)
 		 * First time through, so initialize.  This is shared with the dynamic
 		 * initialization using a DSM.
 		 */
-		injection_point_init_state(inj_state);
+		injection_point_init_state(inj_state, NULL);
 	}
 
 	LWLockRelease(AddinShmemInitLock);
@@ -179,7 +179,7 @@ injection_init_shmem(void)
 	inj_state = GetNamedDSMSegment("injection_points",
 								   sizeof(InjectionPointSharedState),
 								   injection_point_init_state,
-								   &found);
+								   &found, NULL);
 }
 
 /*
diff --git a/src/test/modules/test_dsa/test_dsa.c b/src/test/modules/test_dsa/test_dsa.c
@@ -21,7 +21,7 @@
 PG_MODULE_MAGIC;
 
 static void
-init_tranche(void *ptr)
+init_tranche(void *ptr, void *arg)
 {
 	int		   *tranche_id = (int *) ptr;
 
@@ -39,7 +39,7 @@ test_dsa_basic(PG_FUNCTION_ARGS)
 	dsa_pointer p[100];
 
 	tranche_id = GetNamedDSMSegment("test_dsa", sizeof(int),
-									init_tranche, &found);
+									init_tranche, &found, NULL);
 
 	a = dsa_create(*tranche_id);
 	for (int i = 0; i < 100; i++)
@@ -80,7 +80,7 @@ test_dsa_resowners(PG_FUNCTION_ARGS)
 	ResourceOwner childowner;
 
 	tranche_id = GetNamedDSMSegment("test_dsa", sizeof(int),
-									init_tranche, &found);
+									init_tranche, &found, NULL);
 
 	/* Create DSA in parent resource owner */
 	a = dsa_create(*tranche_id);
diff --git a/src/test/modules/test_dsm_registry/test_dsm_registry.c b/src/test/modules/test_dsm_registry/test_dsm_registry.c
@@ -44,10 +44,13 @@ static const dshash_parameters dsh_params = {
 };
 
 static void
-init_tdr_dsm(void *ptr)
+init_tdr_dsm(void *ptr, void *arg)
 {
 	TestDSMRegistryStruct *dsm = (TestDSMRegistryStruct *) ptr;
 
+	if ((int) (intptr_t) arg != 5432)
+		elog(ERROR, "unexpected arg value %d", (int) (intptr_t) arg);
+
 	LWLockInitialize(&dsm->lck, LWLockNewTrancheId("test_dsm_registry"));
 	dsm->val = 0;
 }
@@ -60,7 +63,7 @@ tdr_attach_shmem(void)
 	tdr_dsm = GetNamedDSMSegment("test_dsm_registry_dsm",
 								 sizeof(TestDSMRegistryStruct),
 								 init_tdr_dsm,
-								 &found);
+								 &found, (void *) (intptr_t) 5432);
 
 	if (tdr_dsa == NULL)
 		tdr_dsa = GetNamedDSA("test_dsm_registry_dsa", &found);

Original file line number	Diff line number	Diff line change
`@@ -858,7 +858,7 @@ autoprewarm_dump_now(PG_FUNCTION_ARGS)`
`858`	`858`	`}`
`859`	`859`
`860`	`860`	`static void`
`861`		`-apw_init_state(void *ptr)`
	`861`	`+apw_init_state(void ptr, void arg)`
`862`	`862`	`{`
`863`	`863`	`AutoPrewarmSharedState state = (AutoPrewarmSharedState ) ptr;`
`864`	`864`
`@@ -880,7 +880,7 @@ apw_init_shmem(void)`
`880`	`880`	`apw_state = GetNamedDSMSegment("autoprewarm",`
`881`	`881`	`sizeof(AutoPrewarmSharedState),`
`882`	`882`	`apw_init_state,`
`883`		`- &found);`
	`883`	`+ &found, NULL);`
`884`	`884`
`885`	`885`	`return found;`
`886`	`886`	`}`