Re: [Haskell-cafe] Re: Threads with high CPU usage

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 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 :

...

On Mon, Dec 22, 2008 at 04:28:03PM -0000, Bayley, Alistair wrote:

...

...

From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@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

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe