I wrote a program that uses a timed thread to collect data from a C producer (using FFI). The number of threads in C producer are fixed (and created at init). One haskell timer thread uses threadDelay to run itself on timed interval. When I look at RTS output after killing the program after couple of timer iterations, I see number of worker tasks increasing with time.<div>
<br></div><div> For example, below is an output after 20 iterations of timer event:<div><br></div><div><div><div>                      MUT time (elapsed)       GC time  (elapsed)</div><div>  Task  0 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)</div>
<div>  Task  1 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)</div><div>  .......output until task 37 snipped as it is same as task 1.......</div><div>  Task 38 (worker) :    0.07s    (  0.09s)       0.00s    (  0.00s)</div>
<div>  Task 39 (worker) :    0.07s    (  0.09s)       0.00s    (  0.00s)</div><div>  Task 40 (worker) :    0.18s    ( 10.20s)       0.00s    (  0.00s)</div><div>  Task 41 (worker) :    0.18s    ( 10.20s)       0.00s    (  0.00s)</div>
<div>  Task 42 (worker) :    0.18s    ( 10.20s)       0.00s    (  0.00s)</div><div>  Task 43 (worker) :    0.18s    ( 10.20s)       0.00s    (  0.00s)</div><div>  Task 44 (worker) :    0.52s    ( 10.74s)       0.00s    (  0.00s)</div>
<div>  Task 45 (worker) :    0.52s    ( 10.75s)       0.00s    (  0.00s)</div><div>  Task 46 (worker) :    0.52s    ( 10.75s)       0.00s    (  0.00s)</div><div>  Task 47 (bound)  :    0.00s    (  0.00s)       0.00s    (  0.00s)</div>
</div></div><div><br></div><div><br></div><div>After two iterations of timer event:</div><div><br></div><div><div>                       MUT time (elapsed)       GC time  (elapsed)</div><div>  Task  0 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)</div>
<div>  Task  1 (worker) :    0.00s    (  0.00s)       0.00s    (  0.00s)</div><div>  Task  2 (worker) :    0.07s    (  0.09s)       0.00s    (  0.00s)</div><div>  Task  3 (worker) :    0.07s    (  0.09s)       0.00s    (  0.00s)</div>
<div>  Task  4 (worker) :    0.16s    (  1.21s)       0.00s    (  0.00s)</div><div>  Task  5 (worker) :    0.16s    (  1.21s)       0.00s    (  0.00s)</div><div>  Task  6 (worker) :    0.16s    (  1.21s)       0.00s    (  0.00s)</div>
<div>  Task  7 (worker) :    0.16s    (  1.21s)       0.00s    (  0.00s)</div><div>  Task  8 (worker) :    0.48s    (  1.80s)       0.00s    (  0.00s)</div><div>  Task  9 (worker) :    0.48s    (  1.81s)       0.00s    (  0.00s)</div>
<div>  Task 10 (worker) :    0.48s    (  1.81s)       0.00s    (  0.00s)</div><div>  Task 11 (bound)  :    0.00s    (  0.00s)       0.00s    (  0.00s)</div></div><div><br></div><div><br></div><div>Haskell code has one forkIO call to kick off C FFI - C FFI creates 8 threads. Runtime options are &quot;-N3 +RTS -s&quot;. timer event is kicked off after forkIO. It is for the form (pseudo-code):</div>
<div><br></div><div>timerevent &lt;other arguments&gt; time = run where run = do threadDelay time &gt;&gt; do some work &gt;&gt; run where &lt;other variables defined for run function&gt;</div><div><br></div></div><div>I also wrote a simpler code using just timer event (fork one timer event, and run another timer event after that), but didn&#39;t see any tasks in RTS output. </div>
<div><br></div><div>I tried searching GHC page for documentation on RTS output, but didn&#39;t find anything that could help me debug above issue. I suspect that timer event is the root cause of increasing number of tasks (with all but last 9 tasks idle -  I guess 8 tasks belong to C FFI, and one task to timerevent thread), and hence, memory leak. </div>
<div><br></div><div>I will appreciate pointers on how to debug it. The timerevent does forkIO a call to send collected data from C FFI to a db server, but disabling that fork still results in the issue of increasing number of tasks. So, it seems strongly correlated with timer event though I am unable to reproduce it with a simpler version of timer event (which removes mvar sync/callback from C FFI).</div>