From 767bc028e5f001351feb498acef9a87c123093d6 Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Fri, 24 Mar 2017 19:27:22 -0300 Subject: [PATCH] Allow DSM segments to be created as pinned dsm_create and dsm_attach assumed that a current resource owner was always in place. Exploration with the API show that this is inconvenient: sometimes one must create a dummy resowner, create/attach the DSM, only to pin the mapping later, which is wasteful. Change create/attach so that if there is no current resowner, the dsm is effectively pinned right from the start. Discussion: https://postgr.es/m/20170324232710.32acsfsvjqfgc6ud@alvherre.pgsql Reviewed by Thomas Munro. --- src/backend/storage/ipc/dsm.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c index 54378bcea9..b65b63b721 100644 --- a/src/backend/storage/ipc/dsm.c +++ b/src/backend/storage/ipc/dsm.c @@ -453,6 +453,13 @@ dsm_set_control_handle(dsm_handle h) /* * Create a new dynamic shared memory segment. + * + * If there is a non-NULL CurrentResourceOwner, the new segment is associated + * with it and must be detached before the resource owner releases, or a + * warning will be logged. If CurrentResourceOwner is NULL, the segment + * remains attached until explicitely detached or the session ends. + * Creating with a NULL CurrentResourceOwner is equivalent to creating + * with a non-NULL CurrentResourceOwner and then calling dsm_pin_mapping. */ dsm_segment * dsm_create(Size size, int flags) @@ -544,6 +551,11 @@ dsm_create(Size size, int flags) * This can happen if we're asked to attach the segment, but then everyone * else detaches it (causing it to be destroyed) before we get around to * attaching it. + * + * If there is a non-NULL CurrentResourceOwner, the attached segment is + * associated with it and must be detached before the resource owner releases, + * or a warning will be logged. Otherwise the segment remains attached until + * explicitely detached or the session ends. See the note atop dsm_create(). */ dsm_segment * dsm_attach(dsm_handle h) @@ -1095,7 +1107,8 @@ dsm_create_descriptor(void) { dsm_segment *seg; - ResourceOwnerEnlargeDSMs(CurrentResourceOwner); + if (CurrentResourceOwner) + ResourceOwnerEnlargeDSMs(CurrentResourceOwner); seg = MemoryContextAlloc(TopMemoryContext, sizeof(dsm_segment)); dlist_push_head(&dsm_segment_list, &seg->node); @@ -1107,7 +1120,8 @@ dsm_create_descriptor(void) seg->mapped_size = 0; seg->resowner = CurrentResourceOwner; - ResourceOwnerRememberDSM(CurrentResourceOwner, seg); + if (CurrentResourceOwner) + ResourceOwnerRememberDSM(CurrentResourceOwner, seg); slist_init(&seg->on_detach);