[PATCH 4/4] Only attempt to ftxwake in sempost if there might be a waiter.
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- Subject: [PATCH 4/4] Only attempt to ftxwake in sempost if there might be a waiter.
- From: iriri <iri@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Reply-to: myrddin-dev@xxxxxxxxxxxxxx
- Date: Sat, 11 Aug 2018 19:15:59 -0700
- To: "myrddin-dev" <myrddin-dev@xxxxxxxxxxxxxx>
--- lib/thread/sem+futex.myr | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/lib/thread/sem+futex.myr b/lib/thread/sem+futex.myr index 434e195d..711dcf93 100644 --- a/lib/thread/sem+futex.myr +++ b/lib/thread/sem+futex.myr @@ -5,13 +5,14 @@ use "futex" pkg thread = type sem = struct - _val : ftxtag + _val : ftxtag + _nwaiters : uint32 ;; - const mksem : (v : uint32 -> sem) - const semwait : (s : sem# -> void) + const mksem : (v : uint32 -> sem) + const semwait : (s : sem# -> void) const semtrywait : (s : sem# -> bool) - const sempost : (s : sem# -> void) + const sempost : (s : sem# -> void) ;; const mksem = {v @@ -21,9 +22,11 @@ const mksem = {v const semwait = {s var v = 0 + xadd(&s._nwaiters, 1) for ; ; while (v = s._val) > 0 if xcas(&s._val, v, v - 1) == v + xadd(&s._nwaiters, -1) -> void ;; ;; @@ -47,6 +50,7 @@ const semtrywait = {s const sempost = {s std.assert((xadd(&s._val, 1) : uint32) != ~0x0, "error: semaphore overflowed\n") - /* Unconditionally wake one waiter */ - ftxwake(&s._val) + if xget(&s._nwaiters) > 0 + ftxwake(&s._val) + ;; } -- 2.18.0
Re: [PATCH 4/4] Only attempt to ftxwake in sempost if there might be a waiter. | Ori Bernstein <ori@xxxxxxxxxxxxxx> |
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