>From 0dfa542f457ebd71640830a993e3a428720b4179 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Wed, 24 Jul 2013 19:34:10 +0200 Subject: [PATCH 1/2] Add slist_delete_current() --- src/backend/lib/ilist.c | 2 +- src/backend/postmaster/bgworker.c | 5 ++++- src/backend/postmaster/postmaster.c | 4 ++-- src/include/lib/ilist.h | 32 +++++++++++++++++++++++++---- src/include/postmaster/bgworker_internals.h | 2 +- 5 files changed, 36 insertions(+), 9 deletions(-) diff --git a/src/backend/lib/ilist.c b/src/backend/lib/ilist.c index 957a118..dddb6eb 100644 --- a/src/backend/lib/ilist.c +++ b/src/backend/lib/ilist.c @@ -28,7 +28,7 @@ * * It is not allowed to delete a 'node' which is is not in the list 'head' * - * Caution: this is O(n) + * Caution: this is O(n), use slist_delete_current() while iterating. */ void slist_delete(slist_head *head, slist_node *node) diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c index ada24e9..9967b69 100644 --- a/src/backend/postmaster/bgworker.c +++ b/src/backend/postmaster/bgworker.c @@ -272,10 +272,13 @@ BackgroundWorkerStateChange(void) * the postmaster. */ void -ForgetBackgroundWorker(RegisteredBgWorker *rw) +ForgetBackgroundWorker(slist_mutable_iter *cur) { + RegisteredBgWorker *rw; BackgroundWorkerSlot *slot; + rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur); + Assert(rw->rw_shmem_slot < max_worker_processes); slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot]; slot->in_use = false; diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index b6b8111..0342be7 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -1452,7 +1452,7 @@ DetermineSleepTime(struct timeval * timeout) if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART) { - ForgetBackgroundWorker(rw); + ForgetBackgroundWorker(&siter); continue; } @@ -5643,7 +5643,7 @@ StartOneBackgroundWorker(void) { if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART) { - ForgetBackgroundWorker(rw); + ForgetBackgroundWorker(&iter); continue; } diff --git a/src/include/lib/ilist.h b/src/include/lib/ilist.h index 73f4115..f8f0458 100644 --- a/src/include/lib/ilist.h +++ b/src/include/lib/ilist.h @@ -211,7 +211,9 @@ typedef struct slist_head * Used as state in slist_foreach(). To get the current element of the * iteration use the 'cur' member. * - * Do *not* manipulate the list while iterating! + * It's allowed to modify the list while iterating, with the sole exception of + * deleting the iterator's current node which may not be deleted unless the + * iteration is not continued afterwards. * * NB: this wouldn't really need to be an extra struct, we could use a * slist_node * directly. We prefer a separate type for consistency. @@ -226,11 +228,12 @@ typedef struct slist_iter * * Used as state in slist_foreach_modify(). * - * Iterations using this are allowed to remove the current node and to add - * more nodes ahead of the current node. + * The only modification allowed while iterating is to remove the current node + * either via slist_delete() or slist_delete_current(). */ typedef struct slist_mutable_iter { + slist_node *prev; /* prev node, for deletions */ slist_node *cur; /* current element */ slist_node *next; /* next node we'll iterate to */ } slist_mutable_iter; @@ -243,7 +246,7 @@ typedef struct slist_mutable_iter /* Prototypes for functions too big to be inline */ -/* Caution: this is O(n) */ +/* Caution: this is O(n), use slist_delete_current() while iterating */ extern void slist_delete(slist_head *head, slist_node *node); #ifdef ILIST_DEBUG @@ -578,6 +581,7 @@ extern slist_node *slist_pop_head_node(slist_head *head); extern bool slist_has_next(slist_head *head, slist_node *node); extern slist_node *slist_next_node(slist_head *head, slist_node *node); extern slist_node *slist_head_node(slist_head *head); +extern void slist_delete_current(slist_mutable_iter *cur); /* slist macro support function */ extern void *slist_head_element_off(slist_head *head, size_t off); @@ -679,6 +683,22 @@ slist_head_node(slist_head *head) { return (slist_node *) slist_head_element_off(head, 0); } + +/* + * Delete the iterator's current element while preserving integrity of the + * underlying list. + */ +STATIC_IF_INLINE void +slist_delete_current(slist_mutable_iter *cur) +{ + /* + * cur->prev will point to the slist_head's 'head' field when the iteration + * is at the first element of the list allowing us to treat perform + * deletion of the first element without a special case. + */ + cur->prev->next = cur->next; +} + #endif /* PG_USE_INLINE || ILIST_INCLUDE_DEFINITIONS */ /* @@ -726,9 +746,13 @@ slist_head_node(slist_head *head) #define slist_foreach_modify(iter, lhead) \ for (AssertVariableIsOfTypeMacro(iter, slist_mutable_iter), \ AssertVariableIsOfTypeMacro(lhead, slist_head *), \ + (iter).prev = &(lhead)->head, \ (iter).cur = (lhead)->head.next, \ (iter).next = (iter).cur ? (iter).cur->next : NULL; \ + \ (iter).cur != NULL; \ + \ + (iter).prev = (iter).cur, \ (iter).cur = (iter).next, \ (iter).next = (iter).next ? (iter).next->next : NULL) diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h index 6484cfb..478a1ff 100644 --- a/src/include/postmaster/bgworker_internals.h +++ b/src/include/postmaster/bgworker_internals.h @@ -39,7 +39,7 @@ extern slist_head BackgroundWorkerList; extern Size BackgroundWorkerShmemSize(void); extern void BackgroundWorkerShmemInit(void); extern void BackgroundWorkerStateChange(void); -extern void ForgetBackgroundWorker(RegisteredBgWorker *); +extern void ForgetBackgroundWorker(slist_mutable_iter *cur); #ifdef EXEC_BACKEND extern BackgroundWorker *BackgroundWorkerEntry(int slotno); -- 1.8.3.251.g1462b67