Allow parent's WaitEventSets to be freed after fork().

An epoll fd belonging to the parent should be closed in the child.  A
kqueue fd is automatically closed by fork(), but we should still adjust
our counter.  For poll and Windows systems, nothing special is required.
On all systems we free the memory.

No caller yet, but we'll need this if we start using WaitEventSet in the
postmaster as planned.

Reviewed-by: Andres Freund <[email protected]>
Discussion: https://postgr.es/m/CA%2BhUKG%2BZ-HpOj1JsO9eWUP%2Bar7npSVinsC_npxSy%2BjdOMsx%3DGg%40mail.gmail.com

2 files changed, 18 insertions, 0 deletions

diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index b32c96b63d3..de4fbcdfb94 100644
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -869,6 +869,23 @@ FreeWaitEventSet(WaitEventSet *set)
 	pfree(set);
 }
 
+/*
+ * Free a previously created WaitEventSet in a child process after a fork().
+ */
+void
+FreeWaitEventSetAfterFork(WaitEventSet *set)
+{
+#if defined(WAIT_USE_EPOLL)
+	close(set->epoll_fd);
+	ReleaseExternalFD();
+#elif defined(WAIT_USE_KQUEUE)
+	/* kqueues are not normally inherited by child processes */
+	ReleaseExternalFD();
+#endif
+
+	pfree(set);
+}
+
 /* ---
  * Add an event to the set. Possible events are:
  * - WL_LATCH_SET: Wait for the latch to be set
diff --git a/src/include/storage/latch.h b/src/include/storage/latch.h
index c55838db607..63a1fc440c4 100644
--- a/src/include/storage/latch.h
+++ b/src/include/storage/latch.h
@@ -175,6 +175,7 @@ extern void ShutdownLatchSupport(void);
 
 extern WaitEventSet *CreateWaitEventSet(MemoryContext context, int nevents);
 extern void FreeWaitEventSet(WaitEventSet *set);
+extern void FreeWaitEventSetAfterFork(WaitEventSet *set);
 extern int	AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd,
 							  Latch *latch, void *user_data);
 extern void ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch);