From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org> To: tarantool-patches@freelists.org Cc: kostja@tarantool.org Subject: [tarantool-patches] [PATCH 2/4] swim: fix a dangerous yield in ffi.gc Date: Fri, 28 Jun 2019 01:25:44 +0200 [thread overview] Message-ID: <0b16f1d70660886a21e0e850ff996e3045652fc4.1561677891.git.v.shpilevoy@tarantool.org> (raw) In-Reply-To: <cover.1561677891.git.v.shpilevoy@tarantool.org> FFI can't survive yields. A yield in ffi.C.func() leads to a crash; yield in ffi.gc is not documented as allowed. Yield in any GC function leads to garbage collector stuck until the yield is finished. This patch makes SWIM GC callback non-yielding. Now yielding swim_delete() is called in a separate fiber created in GC callback, but started at the end of event loop only. Follow up #3234 --- src/lua/swim.lua | 18 +++++++++++++++++- test/swim/swim.result | 30 ++++++++++++++++++++++++++++++ test/swim/swim.test.lua | 12 ++++++++++++ 3 files changed, 59 insertions(+), 1 deletion(-) diff --git a/src/lua/swim.lua b/src/lua/swim.lua index bae6c0da6..686c376cc 100644 --- a/src/lua/swim.lua +++ b/src/lua/swim.lua @@ -3,6 +3,7 @@ local uuid = require('uuid') local buffer = require('buffer') local msgpack = require('msgpack') local crypto = require('crypto') +local fiber = require('fiber') local internal = require('swim') ffi.cdef[[ @@ -948,6 +949,21 @@ swim_cfg_not_configured_mt.__call = swim_cfg_first_call -- removed members erasure - GC drops them automatically. local cache_table_mt = { __mode = 'v' } +-- +-- SWIM garbage collection function. It can't delete the SWIM +-- instance immediately, because it is invoked by Lua GC. Firstly, +-- it is not safe to yield in FFI - Jit can't survive a yield. +-- Secondly, it is not safe to yield in any GC function, because +-- it stops garbage collection. Instead, here a new fiber is +-- created without yields, which works at the end of the event +-- loop, and deletes the instance asynchronously. +-- +local function swim_gc(ptr) + fiber.new(function() + internal.swim_delete(ptr) + end) +end + -- -- Create a new SWIM instance, and configure if @a cfg is -- provided. @@ -969,7 +985,7 @@ local function swim_new(cfg) if ptr == nil then return nil, box.error.last() end - ffi.gc(ptr, internal.swim_delete) + ffi.gc(ptr, swim_gc) local s = setmetatable({ ptr = ptr, cfg = setmetatable({index = {}}, swim_cfg_not_configured_mt), diff --git a/test/swim/swim.result b/test/swim/swim.result index 6004971d0..318b4bed9 100644 --- a/test/swim/swim.result +++ b/test/swim/swim.result @@ -1595,6 +1595,36 @@ s --- - [] ... +-- +-- Check that SWIM GC doesn't block nor crash garbage collector. +-- +s = swim.new() +--- +... +allow_gc = false +--- +... +_ = s:on_member_event(function() while not allow_gc do pcall(fiber.sleep, 0.01) end end) +--- +... +s:cfg({uri = 0, uuid = uuid(1)}) +--- +- true +... +s = setmetatable({s}, {__mode = 'v'}) +--- +... +collectgarbage('collect') +--- +- 0 +... +s +--- +- [] +... +allow_gc = true +--- +... test_run:cmd("clear filter") --- - true diff --git a/test/swim/swim.test.lua b/test/swim/swim.test.lua index f1139087c..16b77b602 100644 --- a/test/swim/swim.test.lua +++ b/test/swim/swim.test.lua @@ -545,4 +545,16 @@ s = setmetatable({s}, {__mode = 'v'}) collectgarbage('collect') s +-- +-- Check that SWIM GC doesn't block nor crash garbage collector. +-- +s = swim.new() +allow_gc = false +_ = s:on_member_event(function() while not allow_gc do pcall(fiber.sleep, 0.01) end end) +s:cfg({uri = 0, uuid = uuid(1)}) +s = setmetatable({s}, {__mode = 'v'}) +collectgarbage('collect') +s +allow_gc = true + test_run:cmd("clear filter") -- 2.20.1 (Apple Git-117)
next prev parent reply other threads:[~2019-06-27 23:24 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-27 23:25 [tarantool-patches] [PATCH 0/4] SWIM amendments Vladislav Shpilevoy 2019-06-27 23:25 ` [tarantool-patches] [PATCH 1/4] swim: fix a leak when a trigger is installed Vladislav Shpilevoy 2019-06-27 23:25 ` Vladislav Shpilevoy [this message] 2019-06-27 23:25 ` [tarantool-patches] [PATCH 3/4] swim: fix inability to set generation only Vladislav Shpilevoy 2019-06-27 23:25 ` [tarantool-patches] [PATCH 4/4] swim: default generation is timestamp Vladislav Shpilevoy 2019-06-28 11:25 ` [tarantool-patches] Re: [PATCH 0/4] SWIM amendments Konstantin Osipov 2019-06-28 21:02 ` Vladislav Shpilevoy
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