Haskell:线程在STM事务中无限期地被阻塞

Question

有没有办法增加一个时间间隔,在此基础上RTS决定该线程在STM事务中无限期地被阻塞？这是我的代码:

import Control.Concurrent (ThreadId)
import Control.Concurrent.MVar (MVar,newMVar,withMVar)
import Control.Concurrent.STM
import qualified Control.Concurrent.ThreadManager as TM

data ThreadManager = ThreadManager { tmCounter::TVar Int, tmTM::MVar TM.ThreadManager }

data Settings = Settings {
    maxThreadsCount::Int }

createThreadManager :: Settings -> IO ThreadManager
createThreadManager s = do
    counter <- atomically $ newTVar (maxThreadsCount s)
    tm <- TM.make >>= newMVar
    return $ ThreadManager counter tm

forkManaged :: ThreadManager -> IO () -> IO ThreadId
forkManaged tm fn = do
    atomically $ do
        counter <- readTVar $ tmCounter tm
        check $ counter > 0
        writeTVar (tmCounter tm) (counter - 1)
    withMVar (tmTM tm) $ \thrdmgr -> TM.fork thrdmgr $ do
        fn
        atomically $ do
            counter <- readTVar $ tmCounter tm
            writeTVar (tmCounter tm) (counter + 1)

forkManaged确保同时运行的托管线程数量不超过maxThreadsCount.它工作正常,直到重负荷.在重负载下,RTS抛出异常.我认为在繁重的负载下,在资源的硬并发竞争中,一些线程没有时间访问STM上下文.所以我认为,当RTS决定抛出此异常时,增加时间间隔可以解决问题.

Answer 1

丹尼尔瓦格纳是对的.该决定不是超时决定.rts中的相关代码在Schedule.c

请参阅resurrectThreads函数以了解抛出异常的位置.该评论描述了这只被抛出到GC之后被发现是垃圾的线程.ezyang描述了这对mvars有何用处:http://blog.ezyang.com/2011/07/blockedindefinitelyonmvar/

[ check当我检查它的来源并且意识到它只是一个简单的警卫/重试并且没有在之前的论文中描述的时候删除了关于删除的糟糕猜测- 哎呀!我现在怀疑Daniel Wagner在这里也是正确的,而且问题是计数器没有增加.]