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1
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+import Control.Concurrent
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2
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+import Control.Concurrent.STM
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3
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+import Control.Exception
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4
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+import Control.Monad
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5
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+
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6
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+-- | Test to make sure that deadlock detection works even when there are other
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7
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+-- unrelated threads that are blocked on I\/O or timeouts.
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8
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+-- Historically however this did affect things in the non-threaded RTS which
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9
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+-- would only do deadlock detection if there were no runnable threads /and/
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10
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+-- no pending I\/O. See <https://gitlab.haskell.org/ghc/ghc/-/issues/26408>
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11
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+main :: IO ()
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12
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+main = do
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13
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+
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14
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+ -- Set up two threads that are deadlocked on each other
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15
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+ aDone <- newTVarIO False
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16
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+ bDone <- newTVarIO False
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17
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+ let blockingThread theirDone ourDone =
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18
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+ atomically $ do
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19
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+ done <- readTVar theirDone
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20
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+ guard done
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21
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+ writeTVar ourDone True
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22
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+ _ <- forkIO (blockingThread bDone aDone)
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23
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+ _ <- forkIO (blockingThread aDone bDone)
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24
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+
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25
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+ -- Set up another thread that is blocked on a long timeout.
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26
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+ --
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+ -- We use a timeout rather than I/O as it's more portable, whereas I/O waits
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28
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+ -- are different between posix and windows I/O managers.
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29
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+ --
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30
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+ -- One gotcha is that when the timeout completes then the deadlock will be
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31
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+ -- detected again (since the bug is about I/O or timeouts masking deadlock
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32
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+ -- detection). So for a reliable test the timeout used here must be longer
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33
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+ -- than the test framework's own timeout. So we use maxBound, and we adjust
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34
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+ -- the test framework's timeout to be short (see run_timeout_multiplier).
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35
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+ _ <- forkIO (threadDelay maxBound)
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36
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+
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37
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+ -- Wait on the deadlocked threads to terminate. We now expect that the threads
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38
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+ -- that are deadlocked are detected as such and an exception is raised.
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39
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+ -- Note that if this fails, the test itself will effectively deadlock and
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40
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+ -- will rely on the test framework's timeout.
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41
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+ atomically $ do
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42
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+ status <- mapM readTVar [aDone, bDone]
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43
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+ guard (or status) |