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{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnliftedFFITypes #-}
import GHC.Prim (StackSnapshot#, ThreadId#)
import GHC.Conc.Sync (ThreadId(..))
import GHC.Stack.CloneStack
import Control.Concurrent
import GHC.Conc
import System.Mem
foreign import ccall "expectStacksToBeEqual" expectStacksToBeEqual:: StackSnapshot# -> ThreadId# -> IO ()
foreign import ccall "expectStackToBeNotDirty" expectStackToBeNotDirty:: StackSnapshot# -> IO ()
-- | Clone the stack of another thread and check it's snapshot for being equal
-- with the live stack.
-- In the meanwhile enforce a garbage collection to ensure that the stack
-- snapshot is still valid afterwards (is not gc'ed while in use).
main :: IO ()
main = do
mVarToBeBlockedOn <- newEmptyMVar
threadId <- forkIO $ immediatelyBlocking mVarToBeBlockedOn
waitUntilBlocked threadId
stackSnapshot <- cloneThreadStack threadId
performMajorGC
let (StackSnapshot stack) = stackSnapshot
let (ThreadId tid#) = threadId
expectStacksToBeEqual stack tid#
expectStackToBeNotDirty stack
immediatelyBlocking :: MVar Int -> IO ()
immediatelyBlocking mVarToBeBlockedOn = do
takeMVar mVarToBeBlockedOn
return ()
waitUntilBlocked :: ThreadId -> IO ()
waitUntilBlocked tid = do
blocked <- isBlocked tid
if blocked then
return ()
else
do
threadDelay 100000
waitUntilBlocked tid
isBlocked:: ThreadId -> IO Bool
isBlocked = fmap isThreadStatusBlocked . threadStatus
isThreadStatusBlocked :: ThreadStatus -> Bool
isThreadStatusBlocked (ThreadBlocked _) = True
isThreadStatusBlocked _ = False
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