Posted to libraries@haskell.org, by Lauri Alanko
[la@iki.fi]:
The following program gets stuck in ghci, and when
compiled with ghc and
run, fails with "Fail: thread blocked indefinitely".
import Data.Array.Diff
main = print (a // [((a ! 0, 1))] ! 0)
where a = array (0,0) [(0,0)] :: DiffArray Int Int
When DiffArray is replaced with Array, it just prints
out "1" as it
should.
Apparently there is some kind of a deadlock internally,
with the update
operation holding the lock already before the lookup
operation is
evaluated.
I think the solution is to evaluate all the indices in
the argument to
replaceDiffArray _before_ obtaining the lock. Changing
a single line in
Diff.hs gives a partial quick fix:
@@ -287 +287 @@
-a `replaceDiffArray` ies = do
+a `replaceDiffArray` ies = sum (map fst ies) `seq` do
However, in DiffUArray, when the underlying imperative
array is unboxed,
the operation is strict also in the elements, and then
(and _only_ then)
the elements, too, need to be evaluated before the MVar
is taken, or
otherwise their evaluation may lead to a deadlock.
I'm not really sure what would be the neatest solution.
Lauri Alanko
la@iki.fi
Trac metadata
| Trac field |
Value |
| Version |
6.2.1 |
| Type |
Bug |
| TypeOfFailure |
OtherFailure |
| Priority |
low |
| Resolution |
ResolvedFixed |
| Component |
libraries/base |
| Test case |
|
| Differential revisions |
|
| BlockedBy |
|
| Related |
|
| Blocking |
|
| CC |
|
| Operating system |
|
| Architecture |
|
