Hi Ryan,
BINGO!
that did it.
Thanks a lot. It certainly works now, finally, eventhough I don't really
know what the implications are.
Günther
Am 23.12.2008, 02:14 Uhr, schrieb Ryan Ingram <ryani.s...@gmail.com>:
You shouldn't need forkOS, but without -threaded (and related RTS
switches to enable multithreading) I think you are sunk. Without
enabling multithreading support, you are saying that your program
(which might use concurrency features of Haskell) will run on a single
OS thread. During a foreign call that never calls back into Haskell,
then, there's no place for the RTS to pre-empt and switch back to
Haskell code.
It's kind of confusing with multiple things named threads; call a
Haskell thread a "lightweight" thread, and an OS thread a "heavy"
thread. Each heavy thread can either be executing Haskell lightweight
threads, or inside a foreign out-call. Once you jump across to
foreign-land, the heavy thread can't do anything (even for a "safe"
out-call) until the out-call either makes an in-call back into Haskell
code, or returns.
Enabling -threaded allows the Haskell runtime to create more heavy
threads; even without -threaded you can make as many lightweight
threads as you like and the runtime will handle scheduling them for
you; a heavy thread can carry many light threads. But a foreign call
takes a whole heavy thread no matter what.
-- ryan
On Mon, Dec 22, 2008 at 1:12 PM, Günther Schmidt <red...@fedoms.com>
wrote:
Hi guys,
I just tried to forkIO-off the database code to keep the UI responsive
using
Takusen with Sqlite this time.
The problem persists though, the UI freezes.
AFAIK the sqlite-Takusen code does not use unsafe ccall which would
block
the thread, so that might not be the cause of the problem after all.
Before you guys make the effort to "fix" this you might see if you can
reproduce the problem maybe uploading a 50 MB file into an Sqlite
database,
for instance, or something else that will keep the database busy for
some
time in a row.
I did not use -threaded and forkOS though.
Günther
Am 22.12.2008, 21:59 Uhr, schrieb John Goerzen <jgoer...@complete.org>:
On Mon, Dec 22, 2008 at 04:28:03PM -0000, Bayley, Alistair wrote:
> From: haskell-cafe-boun...@haskell.org
> [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Günther
Schmidt
>
> I understand that Takusen does not use "unsafe" calls and
> would like to
> try it with that one then, but haven't find enough docs yet
> on how to use
> Takusen.
Not a lot of detailed examples exist for Takusen. I'm hoping the
documentation for Database.Enumerator is a reasonable place to start.
http://darcs.haskell.org/takusen/doc/html/Database-Enumerator.html
I just reviewed the Takusen code and, for no apparent reason, the ODBC
module specifies unsafe for all of its FFI imports, but the other
modules do
not (so they get the default, which I assume is safe). I also was not
aware
of unsafe calls blocking other threads. I'll change the ODBC imports
to be
safe (or rather, unspecified).
Makes sense. I will make the similar change in all HDBC backends.
-- John
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