From 7888b0999488511e4266f2134053fa3a6505a155 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Thu, 19 Nov 2020 18:09:50 +1300 Subject: [PATCH] Add BarrierArriveAndDetachExceptLast(). Provide a way for one process to continue the remaining phases of a (previously) parallel computation alone. Later patches will use this to extend Parallel Hash Join. Author: Melanie Plageman Reviewed-by: Thomas Munro Discussion: https://postgr.es/m/CA%2BhUKG%2BA6ftXPz4oe92%2Bx8Er%2BxpGZqto70-Q_ERwRaSyA%3DafNg%40mail.gmail.com --- src/backend/storage/ipc/barrier.c | 22 ++++++++++++++++++++++ src/include/storage/barrier.h | 1 + 2 files changed, 23 insertions(+) diff --git a/src/backend/storage/ipc/barrier.c b/src/backend/storage/ipc/barrier.c index 3e200e02cc..69afd58689 100644 --- a/src/backend/storage/ipc/barrier.c +++ b/src/backend/storage/ipc/barrier.c @@ -205,6 +205,28 @@ BarrierArriveAndDetach(Barrier *barrier) return BarrierDetachImpl(barrier, true); } +/* + * Arrive at a barrier, and detach all but the last to arrive. Returns true if + * the caller was the last to arrive, and is therefore still attached. + */ +bool +BarrierArriveAndDetachExceptLast(Barrier *barrier) +{ + SpinLockAcquire(&barrier->mutex); + if (barrier->participants > 1) + { + --barrier->participants; + SpinLockRelease(&barrier->mutex); + + return false; + } + Assert(barrier->participants == 1); + ++barrier->phase; + SpinLockRelease(&barrier->mutex); + + return true; +} + /* * Attach to a barrier. All waiting participants will now wait for this * participant to call BarrierArriveAndWait(), BarrierDetach() or diff --git a/src/include/storage/barrier.h b/src/include/storage/barrier.h index d71927cc2f..e0de24378b 100644 --- a/src/include/storage/barrier.h +++ b/src/include/storage/barrier.h @@ -37,6 +37,7 @@ typedef struct Barrier extern void BarrierInit(Barrier *barrier, int num_workers); extern bool BarrierArriveAndWait(Barrier *barrier, uint32 wait_event_info); extern bool BarrierArriveAndDetach(Barrier *barrier); +extern bool BarrierArriveAndDetachExceptLast(Barrier *barrier); extern int BarrierAttach(Barrier *barrier); extern bool BarrierDetach(Barrier *barrier); extern int BarrierPhase(Barrier *barrier); -- 2.39.5