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Sorry if this bug is not related to ghc, but it seems to me that it might be.

Originally I reported it against hedis package, you can find description in it's bug tracker https://github.com/informatikr/hedis/issues/15

Short recap: one specific operation against redis database (zrangebyscoreLimit against big ZSET), program behaves differently. For me, most of the time it would hang, sometimes it succeeds, sometimes outputs "ConnectionLost" twice and dies. My environments are: Ubuntu 12.04/14.04, redis versions tested are 2.2 through 2.8 (latest in each even branch).

Under GHC 7.6 and profiling enabled, strace would end up showing an infinite loop of these operations:

--- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_pid=0, si_uid=0, si_value=0} ---
rt_sigreturn() = -1 EINTR (Interrupted system call)
select(4, [3], [], NULL, NULL) = ? ERESTARTNOHAND (To be restarted if no handler)

Under 7.8.2 profiling enabled, it would also loop, but in few seconds it would hang, produring these last lines of output (plus result of Ctrl+C):

select(4, [3], [], NULL, NULL)          = ? ERESTARTNOHAND (To be restarted if no handler)
--- SIGVTALRM {si_signo=SIGVTALRM, si_code=SI_TIMER, si_pid=0, si_uid=0, si_value=0} ---
timer_settime(0, 0, {it_interval={0, 0}, it_value={0, 0}}, NULL) = 0
rt_sigreturn()                          = -1 EINTR (Interrupted system call)
select(4, [3], [], NULL, NULL^CProcess 16483 detached
 <detached ...>

With profiling disabled on 7.8.2 it would sometimes hang same way as with profiling, but sometimes it would finish with outputting "ConnectionLost" errors (you can find links to full strace output in github hedis issue page linked above).

Sorry again if it's not related to GHC, meanwhile I'll try to investigate further.

Thank you.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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