"C" buffer suggestions??

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Re: number-parameterized types and...

Galchin, Vasili

22 Jun 2008 22 Jun '08

2:47 a.m.

Hello, I want to model an I/O read/write buffer in Haskell and marshall down into ANSI C. 1) ByteString? Or Ptr Word8? 2) What are example values of the types in 1)? Kind regards, Vasili

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Basically I want to model POSIX async io "aiocb"( http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in particular the aiocb field "aio_buf"! Kind regards, Vasili On Sun, Jun 22, 2008 at 1:47 AM, Galchin, Vasili wrote:

...

Hello,

I want to model an I/O read/write buffer in Haskell and marshall down into ANSI C.

1) ByteString? Or Ptr Word8?

2) What are example values of the types in 1)?

Kind regards, Vasili

Adam Langley

1:07 p.m.

2008/6/23 Galchin, Vasili :

...

Basically I want to model POSIX async io "aiocb"( http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in particular the aiocb field "aio_buf"!

That's a mutable buffer, so this has to be pretty low level in your wrapping of the AIO interface. I would keep it as a Ptr Word8 at that point. ByteStrings are probably the correct type for the user visible interface, but I would guess not here. Plus, ByteString data lives in the Haskell heap so could get moved about by the collector. Since an AIO interface is probably going to return while the IO is still in progress, you don't want to stop the collector, but nor do you want the data moving because the kernel's pointer isn't going to move with it. AGL -- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

Galchin, Vasili

4:15 p.m.

On Mon, Jun 23, 2008 at 12:07 PM, Adam Langley wrote:

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2008/6/23 Galchin, Vasili :

...
Basically I want to model POSIX async io "aiocb"( http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in particular the aiocb field "aio_buf"!

That's a mutable buffer, so this has to be pretty low level in your wrapping of the AIO interface. I would keep it as a Ptr Word8 at that point. ByteStrings are probably the correct type for the user visible interface, but I would guess not here.

I tried to write a test value of Word8 without success. Can you give an example?

...

Plus, ByteString data lives in the Haskell heap so could get moved about by the collector. Since an AIO interface is probably going to return while the IO is still in progress, you don't want to stop the collector, but nor do you want the data moving because the kernel's pointer isn't going to move with it.

^^ Interesting about moving around in the heap. I cannot use it for AIO.

...

AGL

-- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

Adam Langley

5 p.m.

On Mon, Jun 23, 2008 at 1:15 PM, Galchin, Vasili wrote:

...

I tried to write a test value of Word8 without success. Can you give an example?

I'm not quite sure what you would want in such an example. See [1] for the malloc function. Then you take the result and wrap it with [2]: fp <- mallocBytes nbytes >>= newForeignPtr finalizerFree When you want to use it, use [3] to unwrap fp and get a raw Ptr Word8. You can pass these to foreign functions any place they expect a uint8_t *, char * etc. [1] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.Marshal.Alloc&name=mallocBytes&mode=func [2] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.ForeignPtr&name=newForeignPtr&mode=func [3] http://www.haskell.org/hoogle/hoodoc.cgi?module=Foreign.ForeignPtr&name=withForeignPtr&mode=func -- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

Don Stewart

5:27 p.m.

agl:

...

2008/6/23 Galchin, Vasili :

...
Basically I want to model POSIX async io "aiocb"( http://uw714doc.sco.com/en/man/html.5/aiocb.5.html) in Haskell .. in particular the aiocb field "aio_buf"!

That's a mutable buffer, so this has to be pretty low level in your wrapping of the AIO interface. I would keep it as a Ptr Word8 at that point. ByteStrings are probably the correct type for the user visible interface, but I would guess not here.

Plus, ByteString data lives in the Haskell heap so could get moved about by the collector. Since an AIO interface is probably going to

ByteStrings are allocated into pinned memory, so they're easy to pass to C and back. It uses the fast 'mallocPlainForeignPtr' api, -- GHC notes: 'mallocPlainForeignPtr' has a heavily optimised -- implementation in GHC. It uses pinned memory in the garbage -- collected heap, as for mallocForeignPtr. So heap allocated and collected, but not moved.

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return while the IO is still in progress, you don't want to stop the collector, but nor do you want the data moving because the kernel's pointer isn't going to move with it.

-- Don

Adam Langley

7:13 p.m.

On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart wrote:

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So heap allocated and collected, but not moved.

My bad. In that case, you might want to work with ByteStrings all the way since it might make building the visible interface (which probably should use ByteStrings) easier. AGL -- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

Galchin, Vasili

9:13 p.m.

ok ..... 1) how do I marshall from ByteString to char * (poke)?? 2) how do I write let x =??? :: Word8 3) how do I write let y = ??? ::ByteString Kind regards, Vasili On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley wrote:

...

On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart wrote:

...
So heap allocated and collected, but not moved.

My bad. In that case, you might want to work with ByteStrings all the way since it might make building the visible interface (which probably should use ByteStrings) easier.

AGL

-- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

Galchin, Vasili

9:18 p.m.

e.g. on Word8 ..... let aiocb = AIOCB{ aioFd=fd, aioLioOpcode=0, aioReqPrio=0, aioOffset=0, aioBuf=??, <<<<<<<<<<<<<<<<<<<<< Ptr Word8 aioBytes=128, aioSigevent=event} ??? Kind regards, Vasili On Mon, Jun 23, 2008 at 8:13 PM, Galchin, Vasili wrote:

...

ok .....

1) how do I marshall from ByteString to char * (poke)??

2) how do I write

let x =??? :: Word8

3) how do I write

let y = ??? ::ByteString

Kind regards, Vasili

On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley wrote:

...
On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart wrote:

...
So heap allocated and collected, but not moved.

My bad. In that case, you might want to work with ByteStrings all the way since it might make building the visible interface (which probably should use ByteStrings) easier.

AGL

-- Adam Langley agl@imperialviolet.org http://www.imperialviolet.org

David Roundy

9:32 p.m.

See the Data.ByteString.Internal docs: http://www.haskell.org/ghc/docs/latest/html/libraries/bytestring/Data-ByteSt... Of course, you'd better not write to the contents of that pointer, or bad things could happen... David On Mon, Jun 23, 2008 at 08:18:23PM -0500, Galchin, Vasili wrote:

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e.g. on Word8 .....

let aiocb = AIOCB{ aioFd=fd, aioLioOpcode=0, aioReqPrio=0, aioOffset=0, aioBuf=??, <<<<<<<<<<<<<<<<<<<<< Ptr Word8 aioBytes=128, aioSigevent=event}

???

Kind regards, Vasili

On Mon, Jun 23, 2008 at 8:13 PM, Galchin, Vasili wrote:

...
ok .....

1) how do I marshall from ByteString to char * (poke)??

2) how do I write

let x =??? :: Word8

3) how do I write

let y = ??? ::ByteString

Kind regards, Vasili

On Mon, Jun 23, 2008 at 6:13 PM, Adam Langley wrote:

...
On Mon, Jun 23, 2008 at 2:27 PM, Don Stewart wrote:

...
So heap allocated and collected, but not moved.

My bad. In that case, you might want to work with ByteStrings all the way since it might make building the visible interface (which probably should use ByteStrings) easier.

AGL

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Adam Langley
David Roundy
Don Stewart
Galchin, Vasili