[Haskell-cafe] Using tiny (atomic) mutables between multiple threads
Hello, Haskell Cafe!
I used an MVar to signalize to many threads, when it's time to finish their
business (I called it a LoopBreaker). Recently I realized, that it might be
too expensive (to use MVar) for cases when threads are many and all of them
read my LoopBreaker intensively. This assumption appeared in a case, where I
widely (in many threads) used my stopableThreadDelay, which checks
LoopBreaker every d = 100 milliseconds.
So I decided that I don't really need all the great features, that MVar
provides, and that a simpler memory usage concept might be applied here. In
a most (machinely) reduced view, all I need is a mutable byte. It would be
thread safe, since reading and writing are atomic operations. I then wrote a
simple experimental module (my first experience with Ptr in Haskell):
-
import Control.Monad
import Foreign.Marshal.Utils
import Foreign.Ptr
import Foreign.Storable
newtype MyVar a = MyVar { mvPtr :: Ptr a }
newMyVar :: Storable a = a - IO (MyVar a)
newMyVar val = MyVar `liftM` new val
readMyVar :: Storable a = (MyVar a) - IO a
readMyVar val = peek $ mvPtr val
writeMyVar :: Storable a = (MyVar a) - a - IO ()
writeMyVar var val = poke (mvPtr var) val
-
Now, please, help me to answer few questions about all it:
1. Might readMVar really be computationally expensive under heavy load,
(with all it's wonderful blocking features)? How much (approximately) more
expensive, comparing to a assembler's mov?
2. Are the above readMyVar and writeMyVar really atomic? Or are they atomic
only if I apply them to MyVar Word8 type?
3. Are the above readMyVar and writeMyVar safe against asynchronous
exceptions? Or again, only if I use MyVar Word8 type?
Belka
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Re: [Haskell-cafe] Using tiny (atomic) mutables between multiple threads
Thank you, Bulat, for both your suggestions! 1. Since Haskell uses 1 byte for Bool (I confidently guess) and it's safe, it would also be safe to use IORef Word8. Moreover, I found http://hackage.haskell.org/packages/archive/ArrayRef/0.1.3.1/doc/html/Data-Ref-Unboxed.html#v%3AmodifyIOURef your module and http://www.haskell.org/haskellwiki/Library/ArrayRef the corresponding article in HaskellWiki , so I plan to use IOURef Word8. I wonder, however, what's the difference between Foreign.Ptr Word8 and IORef Word8 (or IOURef Word8)? 2. As for architecture, I'm not sure that understood the whole suggestion, but got inspired for new ideas for sure! :) My thread's iterations mostly are to acquire resource from load-balancers' chans, and then to react on outer world state changes - networking and DB. I put all the blocking operations to be stoppable by LoopBreaker. There's no real need in job production/execution separation (in most cases) for now (I guess my architecture is not yet mature enough to consist of generalized workers and small business-concept-specific initiative sources; my threads still are very specific to what they are meant to), but I am in need of good resources production/utilization separation. Now in a better architecture I could exchange [stopableThreadDelays between iterations of threads] on [timely sending the LoopBreaker through Chans alone or together with resources (like network handle or the load balancer's permission)]... This way I would definitely minimize some repeating patterns in code, minimize load on LoopBreaker itself, centralize my timing and configuration application management and simplify some resource management processes (like acquiring network handle, when it's required). Added in a ToDo list for next version!.. =) Thanks again! Belka -- View this message in context: http://www.nabble.com/Using-tiny-%28atomic%29-mutables-between-multiple-threads-tp25420972p25430039.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking for an extention (functional incapsulation)
Exponentially? Now I'm missing something... I meant: in as-is version you have 3 declarations (data, sdtField2 :: ..., sdtField2 = ...), but in a proposed one - only one, with subdeclarations. My perception is more oriented on that compositional criterion, than calculates char counts. Besides, syntactically proposed version sticks together entities that are very closely related. -- View this message in context: http://www.nabble.com/Seeking-for-an-extention-%28functional-incapsulation%29-tp24856249p24861049.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Seeking for an extention (functional incapsulation)
Belka wrote: Exponentially? Now I'm missing something... I meant: in as-is version you have 3 declarations (data, sdtField2 :: ..., sdtField2 = ...), but in a proposed one - only one, with subdeclarations. My perception is more oriented on that compositional criterion, than calculates char counts. Besides, syntactically proposed version sticks together entities that are very closely related. I guess, I was too fast calling it (growth of code units with LOC in as-is version against proposed one) exponential. :) It is not. Proportional. But that's not that important. -- View this message in context: http://www.nabble.com/Seeking-for-an-extention-%28functional-incapsulation%29-tp24856249p24861154.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Seeking for an extention (functional incapsulation)
Hello, cafe visitors! :)
This is a double topic:
1. Can't find any good informative resource with descriptions of Haskell
extensions. Could anybody please share good one if it exists?
The only good one I found:
http://hackage.haskell.org/trac/haskell-prime/wiki/HaskellExtensions
But it's a bit too old and not that full...
I undestand, that Haskell is kind of boiling language, in a sense of being
neverending experiment. It develops all the time, extensions show up and
drop out. So it's not that easy to support community with a fresh
information about them. But on the other side, the property (of being
boiling language) makes such information really important for community
members... I think. :)
2. Consider situation:
---
data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 ::
SDT_Field2Type}
sdtField3 :: SomeDataType - SDT_Field3Type
sdtField3 sdt = f (sdtField1 sdt) (sdtField2 sdt)
---
I induced recently, that it would be very comfortable if I could perform in
a way like this:
---
data SomeDataType = SomeDataType { sdtField1 :: SDT_Field1Type, sdtField2 ::
SDT_Field2Type, sdtField3 :: SDT_Field2Type, sdtField3 = f sdtField1
sdtField2}
---
The situation is not that rare, when dealing with nonprimitive data
constructions. Moreover would be really comfortable to reduce
---
data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type,
sdtField2 :: SDT_Field2Type} | SomeDataType_222 { sdtField1 ::
SDT_Field1Type, sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type}
sdtField3 :: SomeDataType - SDT_Field3Type
sdtField3 sdt = case sdt of {SomeDataType_111 - f (sdtField1 sdt)
(sdtField2 sdt) ; SomeDataType_222 - g (sdtField1 sdt) (sdtField2 sdt)
(sdtField5 sdt)}
\/ \/ \/ \/ \/ \/ \/ \/ \/ \/
data SomeDataType = SomeDataType_111 { sdtField1 :: SDT_Field1Type,
sdtField2 :: SDT_Field2Type, sdtField3 :: SDT_Field3Type, sdtField3 = f
sdtField1 sdtField2} | SomeDataType_222 { sdtField1 :: SDT_Field1Type,
sdtField2 :: SDT_Field2Type, sdtField5 :: SDT_Field5Type, sdtField3 ::
SDT_Field3Type, sdtField3 = g sdtField1 sdtField2 sdtField5}
---
Usable mechanics for realization would be:
1. Funtion similar to Data.Function.on (example: (*) `on` f = \x y - f x *
f y), but opposite - I called it under.
t `under` f = \x y - (x f) `t` (y f)
2. currying and uncurrying
Is there any such extension?
Belka
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Re: [Haskell-cafe] Seeking for an extention (functional incapsulation)
Thank you, for your reply, Dan! :) You don't really need this inline in the record syntax, do you? In fact, that was the point. To enclose direct functional dependants into the record declaration. To achieve better pithiness - it's valuable, and the value grows exponentially with LOC (lines of code) count. :) sdtField3 sdt = f $ sdtField1 * sdtField2 Doesn't look much better than my under function (t `under` f = \x y - (x f) `t` (y f)). What did I miss? I believe, there are good reasons to use Control.Applicative for lots purposes, but unfortunately, yet haven't had time to try it in my practice. Belka -- View this message in context: http://www.nabble.com/Seeking-for-an-extention-%28functional-incapsulation%29-tp24856249p24856983.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] typeclasses comprehension problems: situation classes?
Hello, cafe visitors!
I'm trying to learn Haskell typeclasses, - about how to use them, - but
can't handle some conceptiual problems, which confuses me a lot. I took one
real problem (ErrorInfo gragual gathering), to tackle it in my studies: I
have a class of situations: there is an object, and it gets cumulatively
filled (or updated) with content. The code is in the end - it consists of 3
versions:
1. My first try. Fast written, based on intuitive understanding. Failed.
2. The second try - exploring an open world assumption. I hoped this would
set me on the right path. Failure.
3. Surrendered to compiler - statisfied all it's requirements. This code
looks absurd to me: parameter-never-to-be-used, unwanted-defaults. Compiler
accepted this one though.
Problems:
1. How to define *fillerRole* correctly, so that it depends on the
type-value of src_t?
2. How to define *initFillable* correctly, so that it depends only on the
type-value filled_t, which is specified by the context of evaluation?
3. What are my misconcepts in the use of Haskell typeclasses here?
4. Maybe I should distinguish *situation class* (as this one), as something
unavailable in Haskell? This assumption is the last one to make... I'd
rather belive, that there is something I'm not aware of (for a considerably
long time already) in Haskell. A lack of some programming technique
Please, Help!
Regards,
Belka
==TRY=1===DOESN'T=COMPILE==
{-# LANGUAGE MultiParamTypeClasses #-}
class FillsConsideringRoles src_t filled_t role_t where
initFillable :: filled_t
fillerRole :: role_t
fill :: src_t - filled_t - filled_t
data Role = Role1 | Role2 deriving (Show)
data FillableObject = FillableObject
{ foData1 :: Maybe (Int, Role)
, foData2 :: Maybe (Int, Role)
} deriving (Show)
newEmptyFillableObject :: FillableObject
newEmptyFillableObject = FillableObject Nothing Nothing
data Constructor1 = Constructor1 Int
data Constructor2 = Constructor2 Int
instance FillsConsideringRoles Constructor1 FillableObject Role where
initFillable = newEmptyFillableObject
fillerRole = Role1
fill c fo = let (Constructor1 i) = c in fo { foData1 = Just (i,
fillerRole) }
instance FillsConsideringRoles Constructor2 FillableObject Role where
initFillable = newEmptyFillableObject
fillerRole = Role2
fill c fo = let (Constructor2 i) = c in fo { foData2 = Just (i,
fillerRole) }
main = putStrLn $ show $ fill c2 $ fill c1 initFillable
where
c1 = Constructor1 76
c2 = Constructor2 43
==TRY=1==[END]===
==TRY=2===DOESN'T=COMPILE
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverlappingInstances #-}
class FillsConsideringRoles src_t filled_t role_t where
initFillable :: filled_t
fillerRole :: role_t
fill :: src_t - filled_t - filled_t
--
data Role = DefaultRole | Role1 | Role2 deriving (Show)
data FillableObject = FillableObject
{ foData1 :: Maybe (Int, Role)
, foData2 :: Maybe (Int, Role)
} deriving (Show)
newEmptyFillableObject :: FillableObject
newEmptyFillableObject = FillableObject Nothing Nothing
data Constructor1 = Constructor1 Int
data Constructor2 = Constructor2 Int
instance FillsConsideringRoles filler_t filled_t Role where
fillerRole = DefaultRole
instance FillsConsideringRoles Constructor2 filled_t Role where
fillerRole = Role2
instance FillsConsideringRoles Constructor1 filled_t Role where
fillerRole = Role1
instance FillsConsideringRoles filler_t FillableObject role_t where
initFillable = newEmptyFillableObject
instance FillsConsideringRoles Constructor1 FillableObject Role where
fill c fo = let (Constructor1 i) = c in fo { foData1 = Just (i,
fillerRole) }
instance FillsConsideringRoles Constructor2 FillableObject Role where
fill c fo = let (Constructor2 i) = c in fo { foData2 = Just (i,
fillerRole) }
main = putStrLn $ show $ fill c2 $ fill c1 initFillable
where
c1 = Constructor1 76
c2 = Constructor2 43
==TRY=2==[END]===
==TRY=3===WORKS=
{-# LANGUAGE MultiParamTypeClasses #-}
class FillsConsideringRoles src_t filled_t role_t where
initFillable :: ((),src_t, role_t) - filled_t
fillerRole :: ((),src_t, filled_t) - role_t
fill :: ((),role_t) - src_t - filled_t - filled_t
data Role = DefaultRole | Role1 | Role2 deriving (Show)
data FillableObject = FillableObject
[Haskell-cafe] Classes: functional dependency (type - value)
Hello, communion people! I seek for your advice in a matter, where it's really hard for me to determine a good programming style. Here's the problem. I'm generalizing multiple authorization procedures to one, using class definition. (if of any interest, the code is in the end.) The problem essense is folowing: data SomeRole = Role1 | Role2 | Role3 class SomeClass a b c | a - b, c where f1 :: ... f2 :: ... ... fn :: ... role :: SomeRole -- -- here is the problem I want to have a fuctional dependency from a type a on a value of *role*, so that I could easily inspect the *role* from within any other class members. Is it possible? Or do I rougly violate some style traditions? Some real code using wished feature: --- data AuthentificationPurpose = JustValidateInput | JustGenerateForOutput | ValidateInputAndGenerateForOutput type AuthSucceded = Bool class AuthentificationStructure t_env t_realInput t_assumption t_keySet | t_realInput - t_assumptionInput, t_keySet where authentificationPurpose :: AuthentificationPurpose makeAssumption :: t_env - t_realInput - IO (Either ErrorMessage t_assumption) makeFinalKeySet :: (t_realInput, t_assumption) - t_keySet validateRealKeySet_with_Assumed :: t_realInput - t_keySet - Maybe ErrorMessage tryLogTheValidKey :: t_env - (t_realInput, t_assumption) - IO (Maybe ErrorMessage) tryLogTheAuthTry :: t_env - (t_realInput, t_assumption, AuthSucceded) - IO (Maybe ErrorMessage) authentificate :: AuthentificationStructure t_env t_realInput t_assumptionInput t_keySet = t_env - t_businessInput - IO (Either ErrorMessage (t_assumption, t_keySet)) authentificate env realInput = do err_or_assumption - makeAssumption env realInput case err_or_assumption of Left err_msg - return $ Left Error! Assumption maker failed. Lower level error message: ++ err_msg Just assumption - do key_set - makeFinalKeySet (realInput, assumption) err_or_keyset1 - case authentificationPurpose of JustGenerateForOutput - return $ Right key_set JustValidateInput - do mb_failure - validateRealKeySet_with_Assumed t_realInput key_set case mb_failure of Just err_msg - return $ Left Error! Invalid set of auth keys. Lower level error message: ++ err_msg Nothing - return $ Right key_set ValidateInputAndGenerateForOutput err_or_keyset2 - case err_or_keyset1 of Left err_msg - return err_or_keyset1 Right key_set - do mb_failure - tryLogTheValidKey env (realInput, assumption) case mb_failure of Just err_msg - return $ Left Error! Could not log valid key. Lower level error message: ++ err_msg Nothing - return err_or_keyset1 mb_failure - tryLogTheAuthTry env (realInput, assumption, isRight err_or_keyset2) case mb_failure of Just err_msg1 - case err_or_keyset2 of Left err_msg2 - return $ Left (1. ++ err_msg2 ++ \n2. ++ err_msg1) Right _ - return $ Left err_msg1 Nothing - case err_or_keyset2 of Left err_msg - return $ Left err_msg Right key_set - return $ Right (assumption, key_set) - Best regards, Belka -- View this message in context: http://www.nabble.com
Re: [Haskell-cafe] using haskell for a project
Welcome to Haskell! =)
But now I don't know how to dynamically add new spells (new spells can be
created in my gameplay). Since I can't assign a new value to the `spells'
variable (Data.Map.insert returns a new map), I just don't know where to
go.
Do distinguish *pure function* concept and *action with side effects*
concept.
The default in FP (Funct. Progr.) paradigm usualy is *pure function*, if
*action with side effects* is avoidable. Pure functions deal with immutable
memory objects. So in your case, whenever you add a new spell, you get a
new character (since your chacter's essence is a spell list). That way
after calculating *addNewSpell* you will have 2 versions of character: a new
one (with spells list bigger), an the original one. Since old one usualy
drop out of the scope (while program evaluation progresses) it gets *garbage
collected* (note: garbage collection showed up in FP already in 1960s).
addNewSpell :: Character - Spell - Character
addNewSpell char_old_version spell_to_add = ...
main = let char_new_version = addNewSpell char_old_version new_spell in
putStrLn $ show char_new_version
where char_old_version = Charcter {...}
new_spell = Spell { }
Have luck, with the brain rewriting! =)
Belka
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Re: [Haskell-cafe] [tryReadAdvChan :: AdvChan a - IO (Maybe a)] problems
Thanks, Niel. :) You actually motivated me to determine/specify defense requirements - that I should have done long before writing here. Now I'm not experienced in DDoSs defending, so my reasoning here might be a bit voulnerable. Few basic requirements: 1. Server has services that shouldn't be endangered by computational resource starvation. That is why I use load balancing for SAR (Services under Attack Risk). I even use 2 types of load controls: one per each SAR, and the second - above all ARSes. 2. Even when under attack SAR should be able to serve. Of course, it's effective input capability becomes much lower, but requirement here is to provide possible maximum of effectiveness. That is why 2.1. identification of bad request should be fast, and 2.2. request processing should be fair (without starvation on acceptance time). After projecting this /\ specification on architecture plan, the need in *good* tryReadChan is now less sharp. However, it still would be very useful - I also have other applications for it. The *good* tryReadChan would be atomic, immediate, and with determinate result (of type Maybe)... -- By the way, for Actually, am I wrong thinking, that it can't be helped - and the degradation from cute concurency synchronization model of Chan is unavoidable? I have an idea of such solution (without getting down to lower level programming), - called it fishing: one should complicate the flow unit (FlowUnit), that is being passed in the Channel. The FlowUnit diversifies to real bizness data, and service data. That way I now may gain control over blocking But this solution is not simple and lightweight. If anybody is interested, I could describe the concept in more details. Belka Neil Davies-2 wrote: Belka You've described what you don't want - what do you want? Given that the fundamental premise of a DDoS attack is to saturate resources so that legitimate activity is curtailed - ultimately the only response has to be to discard load, preferably not the legitimate load (and therein lies the nub of the problem). What are you trying to achieve here - a guarantee of progress for the system? a guarantee of a fairness property? (e.g. some legitimate traffic will get processed) or, given that the DDoS load can be identified given some initial computation, guarantee to progress legitimate load up to some level of DDoS attack? Neil -- View this message in context: http://www.nabble.com/-tryReadAdvChan-%3A%3A-AdvChan-a--%3E-IO-%28Maybe-a%29--problems-tp23328237p23343213.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [tryReadAdvChan :: AdvChan a - IO (Maybe a)] problems
Hi!
I need this function with requirement of heavy reads, *possibly under DDoS
attack*.
Was trying to write such function, but discovered some serious problems of
** possible racings,
** possible starvations
** unbalance: readAdvChan users may get better service than ones of
tryReadAdvChan
These are totally unacceptible for my case of DDoS risk.
Actually, am I wrong thinking, that it can't be helped - and the degradation
from cute concurency synchronization model of Chan is unavoidable?
My (untested) code:
---
---
module AdvChan ( AdvChan
, newAdvChan
, readAdvChan
, writeAdvChan
, writeList2AdvChan
, advChan2StrictList
, withResourceFromAdvChan
, tryReadAdvChan
, isEmptyAdvChan
) where
import Control.Concurrent.Chan
import Control.Concurrent.MVar
data AdvChan a = AdvChan {
acInst:: MVar Chan a
, acWrite :: a - IO ()
, acIsEmpty :: IO Bool
}
newAdvChan :: IO AdvChan a
newAdvChan = do ch- newChan
mv_ch - newMVar ch
return AdvChan {
acInst= mv_ch
, acWrite = writeChan ch
, acIsEmpty = isEmptyChan ch
}
readAdvChan :: AdvChan a - IO a
readAdvChan ach = modifyMVar (acInst ach)
(\ ch - do a - readChan ch
return (ch, a)
)
writeAdvChan :: AdvChan a - a - IO ()
writeAdvChan = acWrite
writeList2AdvChan :: AdvChan a - [a] - IO ()
writeList2AdvChan ach[] = return ()
writeList2AdvChan ach (h:t) = writeAdvChan ach h writeList2AdvChan ach t
advChan2StrictList :: AdvChan a - IO [a]
advChan2StrictList ach = modifyMVar (acInst ach)
(\ ch - let readLoop = do emp -
isEmptyChan ch
case emp of
True -
return []
False -
do _head - readChan ch
_rest - readLoop
return (_head : _rest)
in liftTuple (return ch,
readLoop)
)
withResourceFromAdvChan :: AdvChan a - (\ a - IO (a, b)) - IO b
withResourceFromAdvChan ach f = do res - readAdvChan ach
(res_processed, result) - f res
writeAdvChan ach res_processed
return result
isEmptyAdvChan :: AdvChan a - IO Bool
isEmptyAdvChan = acIsEmpty
microDelta = 50
tryReadAdvChan :: AdvChan a - IO (Maybe a)
tryReadAdvChan ach = emp2Maybeness $ do mb_inst - tryTakeMVar (acInst ach)
case mb_inst of
Nothing - emp2Maybeness
(threadDelay microDelta tryReadAdvChan ach)
Just chan - do emp -
isEmptyChan ch
result - case
emp of
True - return Nothing
False - Just `liftM` readChan ch
putMVar (acInst
ach) chan
return result
where emp2Maybeness f = do emp - isEmptyAdvChan ach
case emp of
True - return Nothing
False - f
---
---
Later after writing my own code, and understanding the problem I checked
Hackage. Found synchronous-channels package there
(http://hackage.haskell.org/cgi-bin/hackage-scripts/package/synchronous-channels),
but it isn't any further in solving my the unbalacedness problems.
Any suggestions on the fresh matter are welcome.
Belka.
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Re: [Haskell-cafe] controlling timeout for Network.Socket.connect - how?
Thanks, Manlio! What system? ArchLinux (2.6.27) Is the timeout the same with a plain C program? Didn't try yet... ^__^ I know that controlling timeout is somehow connected to select(2) Yes. The only working method is to set the socket to non blocking mode, and use select (or poll/epoll/kqueue). Thanks, now I'm confident, that am on the right way! ^__^ I wonder, if *select* really blocks the whole process... or blocks just the green thread, that called it?.. It doesn't depend from being safe/unsafe FFI-ed, does it? Belka -- View this message in context: http://www.nabble.com/controlling-timeout-for-Network.Socket.connect---how--tp22139581p22235312.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] controlling timeout for Network.Socket.connect - how?
Thanks, Manlio! What system? A r c h Linux (2.6.27) Is the timeout the same with a plain C program? Didn't try yet... ^__^ I know that controlling timeout is somehow connected to select(2) Yes. The only working method is to set the socket to non blocking mode, and use select (or poll/epoll/kqueue). Thanks, now I'm confident, that am on the right way! ^__^ I wonder, if *select* really blocks the whole process... or blocks just the green thread, that called it?.. It doesn't depend from being safe/unsafe FFI-ed, does it? Belka -- View this message in context: http://www.nabble.com/controlling-timeout-for-Network.Socket.connect---how--tp22139581p22236279.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] controlling timeout for Network.Socket.connect - how?
It's hard to belive, that nobody ever tackled/solved the subj. problem. I
still can delay a bit solving it, in hope somebody would share experience.
Regards,
Belka
Belka wrote:
Hello, communion people!
I have a problem and ask for an advice.
I'm dealing with sockets on *Linux* platform (Network.Socket). The problem
is that I can't fully control timeout for (connect :: Socket - SockAddr
- IO ()) operation.
On my system the timeout is - 3 seconds - I want to be able to change that
in run-time. Well I managed to find out how to make it LESS THAN 3 seconds
- using System.Timeout. But how to make timeout bigger (for example 9
seconds) is a mystery.
(Notice: in order to achieve 9 seconds timeout - just repeating *connect*
3 times won't be effective for long-slow-way-connections. So it's not a
solution.)
The source code of Network.Socket.connect, taken from darcs:
-
-- Connecting a socket
--
-- Make a connection to an already opened socket on a given machine
-- and port. assumes that we have already called createSocket,
-- otherwise it will fail.
--
-- This is the dual to $bindSocket$. The {\em server} process will
-- usually bind to a port number, the {\em client} will then connect
-- to the same port number. Port numbers of user applications are
-- normally agreed in advance, otherwise we must rely on some meta
-- protocol for telling the other side what port number we have been
-- allocated.
connect :: Socket -- Unconnected Socket
- SockAddr -- Socket address stuff
- IO ()
connect sock@(MkSocket s _family _stype _protocol socketStatus) addr = do
modifyMVar_ socketStatus $ \currentStatus - do
if currentStatus /= NotConnected
then
ioError (userError (connect: can't peform connect on socket in status
++
show currentStatus))
else do
withSockAddr addr $ \p_addr sz - do
let connectLoop = do
r - c_connect s p_addr (fromIntegral sz)
if r == -1
then do
rc - c_getLastError
case rc of
10093 - do -- WSANOTINITIALISED
withSocketsDo (return ())
r - c_connect s p_addr (fromIntegral sz)
if r == -1
then (c_getLastError = throwSocketError connect)
else return r
_ - throwSocketError connect rc
else return r
connectBlocked = do
#if !defined(__HUGS__)
threadWaitWrite (fromIntegral s)
#endif
err - getSocketOption sock SoError
if (err == 0)
then return 0
else do ioError (errnoToIOError connect
(Errno (fromIntegral err))
Nothing Nothing)
connectLoop
return Connected
-
I know that controlling timeout is somehow connected to select(2) (I'm
currently investigating this matter...), but it's not in the Network or
Network.Socket libs (but in the libs that they FFI with).
Hope I won't have to rewrite these low-level functions __
Could anybody, please share some experience on how to adjust timeout for
*connect*?
Thanks in advance,
Best regards,
Belka
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[Haskell-cafe] controlling timeout for Network.Socket.connect - how?
Hello, communion people!
I have a problem and ask for an advice.
I'm dealing with sockets on *Linux* platform (Network.Socket). The problem
is that I can't fully control timeout for (connect :: Socket - SockAddr -
IO ()) operation.
On my system the timeout is - 3 seconds - I want to be able to change that
in run-time. Well I managed to find out how to make it LESS THAN 3 seconds -
using System.Timeout. But how to make timeout bigger (for example 9 seconds)
is a mystery.
(Notice: in order to achieve 9 seconds timeout - just repeating *connect* 3
times won't be effective for long-slow-way-connections. So it's not a
solution.)
The source code of Network.Socket.connect, taken from darcs:
-
-- Connecting a socket
--
-- Make a connection to an already opened socket on a given machine
-- and port. assumes that we have already called createSocket,
-- otherwise it will fail.
--
-- This is the dual to $bindSocket$. The {\em server} process will
-- usually bind to a port number, the {\em client} will then connect
-- to the same port number. Port numbers of user applications are
-- normally agreed in advance, otherwise we must rely on some meta
-- protocol for telling the other side what port number we have been
-- allocated.
connect :: Socket -- Unconnected Socket
- SockAddr -- Socket address stuff
- IO ()
connect sock@(MkSocket s _family _stype _protocol socketStatus) addr = do
modifyMVar_ socketStatus $ \currentStatus - do
if currentStatus /= NotConnected
then
ioError (userError (connect: can't peform connect on socket in status
++
show currentStatus))
else do
withSockAddr addr $ \p_addr sz - do
let connectLoop = do
r - c_connect s p_addr (fromIntegral sz)
if r == -1
then do
rc - c_getLastError
case rc of
10093 - do -- WSANOTINITIALISED
withSocketsDo (return ())
r - c_connect s p_addr (fromIntegral sz)
if r == -1
then (c_getLastError = throwSocketError connect)
else return r
_ - throwSocketError connect rc
else return r
connectBlocked = do
#if !defined(__HUGS__)
threadWaitWrite (fromIntegral s)
#endif
err - getSocketOption sock SoError
if (err == 0)
then return 0
else do ioError (errnoToIOError connect
(Errno (fromIntegral err))
Nothing Nothing)
connectLoop
return Connected
-
I know that controlling timeout is somehow connected to select(2) (I'm
currently investigating this matter...), but it's not in the Network or
Network.Socket libs (but in the libs that they FFI with).
Hope I won't have to rewrite these low-level functions __
Could anybody, please share some experience on how to adjust timeout for
*connect*?
Thanks in advance,
Best regards,
Belka
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[Haskell-cafe] estimating the speed of operation
Hello, communion people! I have a little problem and ask for an advice. I'm trying to estimate the performance speed of one pure function, but get some strange results. - import qualified module Data.ByteString.Lazy.Char8 as L8 import module Data.Digest.Pure.MD5 import module System.IO.Unsafe import module System.Time import module System.Random import module Data.Char clockTime2Tuple (TOD sec pic) = (sec, pic) getClockTimeTuple = getClockTime = (\ x - return $ clockTime2Tuple x) subTimeTuples (s2,ps2) (s1,ps1) = let dps = ps2-ps1 in let (s,ps) = (s2-s1-(if dps0 then 1 else 0), if dps0 then dps+(10^12) else dps) in (s, (div) ps (10^6)) test_md5 test_input n = flip mapM test_input ( \ input_row - do t1 - getClockTimeTuple sequence_ (replicate n (return $ md5 input_row)) t2 - getClockTimeTuple dt - subTimeTuples t2 t1 return (dt) ) test_list = [ pack Hello world!] ++ [L8.replicate 100 ':'] - The results are (iterations_count, microseconds): (1000, [105,105]) (+/- 10) (1, [1000,950]) (+/- 50) (10, [9050,9000]) (+/- 50) (100, [89200,89150]) (+/- 100) - I suspect following problems, which make the results non-objective: 1. I cant get out of laziness 2. I don't turn off GHC internal optimizers So, perhaps, GHC evaluates the MD5 once, but cycles on something else?.. For now I can only guess. Could anybody, please clarify and maybe suggest configuration, which would allow objective speed estimation? Thanks in advance, Best regards, Belka -- View this message in context: http://www.nabble.com/estimating-the-speed-of-operation-tp22075843p22075843.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] estimating the speed of operation
Thanks alot, Bulat! New results are much better: --- test_list = [L8.pack Hello world!] ++ [L8.replicate 100 ':'] --- The results are (iterations_count, microseconds): (1000, [300 +/- 200 , 18400 +/- 100]) (1, [1030 +/- 10 , 19950 +/- 50 ]) (10, [9100 +/- 100 , 55000 +/- 15000]) (100, [89850 +/- 500 ,185000 +/- 500 ]) I also played a bit with bang patterns, to make input stricter, but this gave the same result. --- For the first test string time grow almost linearly, what can't be said about the second string. I still wonder if (and how) GHC optimizes the process. Belka -- View this message in context: http://www.nabble.com/estimating-the-speed-of-operation-tp22075843p22078560.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[Haskell-cafe] cursive referencing
Great thanks, Ryan and Yevgeny! 1. For sumAA 10 $ f 1 2 and for sumAA 1000 $ f 1 2 - does the used memory amounts differ? 2. Does it create in memory only 2 data objects, or creates 10s and 1000s and garbage collects unneeded? -- Also consider fix (\p - (AA somedata1 $ snd p, BB somedata2 $ fst p)) and my mod (added some_very_expensive_f) fix (\p - (AA (some_very_expensive_f somedata1) $ snd p, BB (some_very_expensive_f somedata2) $ fst p)) 2. Does the sumAA evaluates this some_very_expensive_f every iteration of recursion, or is it evaluated only once? Belka Your definition with fix isn't lazy enough, so it goes into an infinite loop. You need to match lazily on the pair; here's a better body for fix: fix (\p - (AA somedata1 $ snd p, BB somedata2 $ fst p)) To prove that the structure really turns out cyclic, you can use Debug.Trace: import Debug.Trace (trace) import Data.Function (fix) data AA = AA Int BB deriving Show data BB = BB Int AA deriving Show f = \data1 data2 - fst $ fix $ \p - (trace eval_aa $ AA data1 $ snd p, trace eval_bb $ BB data2 $ fst p) sumAA 0 _ = 0 sumAA n (AA v bb) = trace sumAA (v + sumBB (n-1) bb) sumBB 0 _ = 0 sumBB n (BB v aa) = trace sumBB (v + sumAA (n-1) aa) main = print $ sumAA 10 $ f 1 2 *Main main eval_aa sumAA eval_bb sumBB sumAA sumBB sumAA sumBB sumAA sumBB sumAA sumBB 15 -- View this message in context: http://www.nabble.com/Recursive-referencing-tp21722002p21756221.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[Haskell-cafe] cursive referencing
Yes. f somedata1 somedata2 = aa where aa = AA somedata1 bb bb = BB somedata2 aa Spasibo, Yevgeny! Originally I was thinking theoretically about a single plain lambda-expression, like (\ somedata1 somedata2 - (\ aa bb - aa (bb aa)) (\ b - AA somedata1 b) (\ a - BB somedata2 a) ) But in the code aa (bb aa) last aa stays lacking an argument, of course, if we don't consider 1st application aa ( as having a side effect on aa. And that's where separate and rule shows up it's power (speaking about where and namespacing in general). =) Belka -- View this message in context: http://www.nabble.com/Recursive-referencing-tp21722002p21722503.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[Haskell-cafe] cursive referencing
Hello!
I'm puzzled, if in Haskell it's possible to create a (pure) data structure,
consisting of 2 substructures referencing each other:
-
data AA = AA {
someData1 :: SomeData1
bb :: BB
}
data BB = BB {
someData2 :: SomeData2
aa :: AA
}
f :: SomeData1 - SomeData2 - AA
f somedata1 somedata2 = ??
-- Always True:
ghci f == aa $ bb f
True
-
Any ideas?
Belka
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Re: [Haskell-cafe] how to implement daemon start and stop directives?
If you want a normal daemon, you want to look at System.Posix.Process to create a proper daemon (forkProcess, createSession; don't forget to close stdOutput (and, errr, Haskell library types: stdin and stderr are where? not System.Posix.IO with stdOutput) and reopen them on / dev/null, at least if they're ttys as determined by System.Posix.Terminal.queryTerminal). You also want to write out a pidfile (/var/run/programname.pid) for use by startproc / killproc, and you want to install a handler for sigTERM (System.Posix.Signals.installHandler) which sets the exit flag (TVar, MVar, IORef, Chan, take your pick). Ideally you also catch sigHUP and reload your state. Thanks for the guide, Brandon !! By the way, I found a piece of code with function (daemonize :: IO () - IO ()) (http://sneakymustard.com/2008/12/11/haskell-daemons), which is close to the subject. I guess now I'm ready to implement my own daemon! Thanks for your help, everyboby!! =) -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp21598690p21647723.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to implement daemon start and stop directives?
You can abstract this pattern: -- runs its argument in an infinite loop, and returns an action that stops the loop daemon :: IO () - IO (IO ()) daemon action = do stopvar - atomically $ newTVar False let run = do stop - atomically $ readTVar stopvar if stop then return () else (action run) forkIO run return (atomically $ writeTVar stopvar True) TVars are overkill here, actually, an IORef would be just fine, I think. Luke Thanks, Luke! Why do you write return (atomically $ writeTVar stopvar True) in the end? Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe... Belka -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp21598690p21599567.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] how to implement daemon start and stop directives?
Hi! Could somebody please share some experience on how to implement daemon start and stop directives. In theory I need something like this: 1. my_daemon start - starts my app with an infinite loop of serving inside. 2. my_daemon stop - puts in some TVar a value signalizing, that stop is given - infinite loop brakes. 3. ...it on Linux platform. Thanks in advance! -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp21598690p21598690.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Connect to DBMS - what's the cost
Hello, community people! Is anybody aware, what aproximately is the cost for the acquiring connection to DB (and also disconnecting from it)? I guess that may differ from DBMS to DBMS, so I mostly am interested in PostgreSQL case, but for other DBMS it's also good to know. Actually, since all Haskell libraries, that provide interfaces to DBMS, use foreign functions, - the question should be focused on commonly used C libraries. Thanks in advance! -- View this message in context: http://www.nabble.com/Connect-to-DBMS---what%27s-the-cost-tp21275600p21275600.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell, successing crossplatform API standart: first feedback
Thanks everybody for your responses, they helped a lot. And sorry for my misconcept on JSON. ;] Sterling Clover, Nov 30, 2008: These days, however, web services seem to be moving towards a RESTful model with a JSON layer and there are plenty of JSON libraries on hackage, which you could just throw over the fastCGI bindings. Alternately you could try JSON over one of the really lightweight haskell web servers, such as shed [2] or lucu [3]. If you go the atter route, I'd love to hear how it went. So here is my first feedback. I hope that's something like an introduction to my futher feedbacks. 1. I started with HAppS. But found it lacking some good definitions. Moreover, I'm still a newbie and not yet confident with monads, so when I accidently saw this: Author's Note: Due to my inexperience with Monads, these explanations are probably lacking. Feel free to improve them. (HAppS tutorial2, sect. 1.1), I felt myself standing on a risky ground, where the risk is to get Monads wronger than wrong. So I decided to check Lucu and return to HAppS later (when I'm invincible). 2. I loved Lucu, and feel respect to it's developer. The code is nice and tidy, one can feel good style in it. Looks like Lucu author achieved great technique in Haskell, knew, how to use Monads and laziness in full power. However I still didn't understand some aspects (simply becase of lacking experience). I sucessfully managed to write a helloworld which connected to DB and provided simple WEB interface. 3. I also tried shed httpd, which is the most minimalistic WEB server. This looks like the best start for a newbie, who isn't confident with monads yet. I manager a small comparison of Lucu and Shed responce times - Lucu was 2 times faster for 1 simple query, which returned 5 rows from small DB. Now I'm planning 1. To try some modification of Lucu, so it has a DB connection in it's environment and some basic triggering (providing conditioned actions after WEB interaction process). 2. Implement one simple project on it. Regards, Belka -- View this message in context: http://www.nabble.com/Haskell%2C-successing-crossplatform-API-standart-tp20742743p21280480.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell, successing crossplatform API standart
Hello! (1) Is anybody aware of SOA approach being supported in Haskell? Found HAIFA package (SOAP, WEB services), but it seems to be a RIP project (with it's last updated in 2006) - trying to install it is a total mess (for me, a newby). (2) Please, perhaps experienced developers could suggest any better crossplatform (crosslanguage) API standart supported in Haskell? For me the main priority is orientation on being supported everywhere in far future... Thanks in advance -- View this message in context: http://www.nabble.com/Haskell%2C-successing-crossplatform-API-standart-tp20742743p20742743.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Could not find module ... which is hidden problem
Hello! START-- $ sudo runghc Setup configure --user Configuring HCL-1.2... $ sudo runghc Setup build Preprocessing library HCL-1.2... Preprocessing executables for HCL-1.2... Building HCL-1.2... HCL.hs:302:7: Could not find module `System.Random': it is a member of package random-1.0.0.1, which is hidden $ sudo ghc-pkg expose random Saving old package config file... done. Writing new package config file... done. $ sudo runghc Setup configure --user Configuring HCL-1.2... $ sudo runghc Setup build Preprocessing library HCL-1.2... Preprocessing executables for HCL-1.2... Building HCL-1.2... HCL.hs:302:7: Could not find module `System.Random': it is a member of package random-1.0.0.1, which is hidden -THE-END Perhaps, i'm 1000th, who asks how to solve this. Sorry that didn't search better, but it's really tiring for a newby. :-( [ http://www.haskell.org/haskellwiki/Upgrading_packages/Updating_to_GHC_6.8 Here ] found something, which maybe called a gentle explaination of what's going on. I have ghc ver: 6.8.2, base ver: 3.0.1.0. So there are 2 questions of mine: (1) Is there any centralized and well organized Haskell Knowledge Base, where it would be much easier to find solutions for popular problems? Anybody, please, your recommendations. (2) As for the topic: the only option for me would be obtaining older GHC (base?) - is that correct? So that require me reinstalling every Haskell package I have installed so far? Thanks in advance. -- View this message in context: http://www.nabble.com/%22Could-not-find-module-...-which-is-hidden%22-problem-tp20742582p20742582.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What *not* to use Haskell for
(1) Function as a system of N concurrent inputs and 1 output is easy essence. How about function as N concurrent inputs and M concurrent outputs? I think it's not native to lambda calculus. So system's programming (if we ever had such paradigm) would solve this issue, while criticizing all FP. (2) For me, I hope this category (What *not* to use Haskell for) won't include SOA. That's what I'am currently trying to decide. (3) I think if CPU's would be lambda-based, not imperative, and paradigm be stronger, most of the why *not* to use Haskell's would be solved, and imperative would be in opposition instead.. with it's enthusiasts. =) They would have good answers for your question. -- View this message in context: http://www.nabble.com/What-*not*-to-use-Haskell-for-tp20436980p20755239.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
