diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,10 @@ +# Revision history for lazy-cache + +## 0.2.0.0 -- 2022-02-06 + + * use clock for managing time periods instead of thyme; + * remove extra dependencies; + +## 0.1.0.0 -- 2020-11-15 + +* Initial layout diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,373 @@ +Mozilla Public License Version 2.0 +================================== + +1. Definitions +-------------- + +1.1. "Contributor" + means each individual or legal entity that creates, contributes to + the creation of, or owns Covered Software. + +1.2. "Contributor Version" + means the combination of the Contributions of others (if any) used + by a Contributor and that particular Contributor's Contribution. + +1.3. "Contribution" + means Covered Software of a particular Contributor. + +1.4. "Covered Software" + means Source Code Form to which the initial Contributor has attached + the notice in Exhibit A, the Executable Form of such Source Code + Form, and Modifications of such Source Code Form, in each case + including portions thereof. + +1.5. "Incompatible With Secondary Licenses" + means + + (a) that the initial Contributor has attached the notice described + in Exhibit B to the Covered Software; or + + (b) that the Covered Software was made available under the terms of + version 1.1 or earlier of the License, but not also under the + terms of a Secondary License. + +1.6. "Executable Form" + means any form of the work other than Source Code Form. + +1.7. "Larger Work" + means a work that combines Covered Software with other material, in + a separate file or files, that is not Covered Software. + +1.8. "License" + means this document. + +1.9. "Licensable" + means having the right to grant, to the maximum extent possible, + whether at the time of the initial grant or subsequently, any and + all of the rights conveyed by this License. + +1.10. "Modifications" + means any of the following: + + (a) any file in Source Code Form that results from an addition to, + deletion from, or modification of the contents of Covered + Software; or + + (b) any new file in Source Code Form that contains any Covered + Software. + +1.11. "Patent Claims" of a Contributor + means any patent claim(s), including without limitation, method, + process, and apparatus claims, in any patent Licensable by such + Contributor that would be infringed, but for the grant of the + License, by the making, using, selling, offering for sale, having + made, import, or transfer of either its Contributions or its + Contributor Version. + +1.12. "Secondary License" + means either the GNU General Public License, Version 2.0, the GNU + Lesser General Public License, Version 2.1, the GNU Affero General + Public License, Version 3.0, or any later versions of those + licenses. + +1.13. "Source Code Form" + means the form of the work preferred for making modifications. + +1.14. "You" (or "Your") + means an individual or a legal entity exercising rights under this + License. For legal entities, "You" includes any entity that + controls, is controlled by, or is under common control with You. For + purposes of this definition, "control" means (a) the power, direct + or indirect, to cause the direction or management of such entity, + whether by contract or otherwise, or (b) ownership of more than + fifty percent (50%) of the outstanding shares or beneficial + ownership of such entity. + +2. License Grants and Conditions +-------------------------------- + +2.1. Grants + +Each Contributor hereby grants You a world-wide, royalty-free, +non-exclusive license: + +(a) under intellectual property rights (other than patent or trademark) + Licensable by such Contributor to use, reproduce, make available, + modify, display, perform, distribute, and otherwise exploit its + Contributions, either on an unmodified basis, with Modifications, or + as part of a Larger Work; and + +(b) under Patent Claims of such Contributor to make, use, sell, offer + for sale, have made, import, and otherwise transfer either its + Contributions or its Contributor Version. + +2.2. Effective Date + +The licenses granted in Section 2.1 with respect to any Contribution +become effective for each Contribution on the date the Contributor first +distributes such Contribution. + +2.3. Limitations on Grant Scope + +The licenses granted in this Section 2 are the only rights granted under +this License. No additional rights or licenses will be implied from the +distribution or licensing of Covered Software under this License. +Notwithstanding Section 2.1(b) above, no patent license is granted by a +Contributor: + +(a) for any code that a Contributor has removed from Covered Software; + or + +(b) for infringements caused by: (i) Your and any other third party's + modifications of Covered Software, or (ii) the combination of its + Contributions with other software (except as part of its Contributor + Version); or + +(c) under Patent Claims infringed by Covered Software in the absence of + its Contributions. + +This License does not grant any rights in the trademarks, service marks, +or logos of any Contributor (except as may be necessary to comply with +the notice requirements in Section 3.4). + +2.4. Subsequent Licenses + +No Contributor makes additional grants as a result of Your choice to +distribute the Covered Software under a subsequent version of this +License (see Section 10.2) or under the terms of a Secondary License (if +permitted under the terms of Section 3.3). + +2.5. Representation + +Each Contributor represents that the Contributor believes its +Contributions are its original creation(s) or it has sufficient rights +to grant the rights to its Contributions conveyed by this License. + +2.6. Fair Use + +This License is not intended to limit any rights You have under +applicable copyright doctrines of fair use, fair dealing, or other +equivalents. + +2.7. Conditions + +Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted +in Section 2.1. + +3. Responsibilities +------------------- + +3.1. Distribution of Source Form + +All distribution of Covered Software in Source Code Form, including any +Modifications that You create or to which You contribute, must be under +the terms of this License. You must inform recipients that the Source +Code Form of the Covered Software is governed by the terms of this +License, and how they can obtain a copy of this License. You may not +attempt to alter or restrict the recipients' rights in the Source Code +Form. + +3.2. Distribution of Executable Form + +If You distribute Covered Software in Executable Form then: + +(a) such Covered Software must also be made available in Source Code + Form, as described in Section 3.1, and You must inform recipients of + the Executable Form how they can obtain a copy of such Source Code + Form by reasonable means in a timely manner, at a charge no more + than the cost of distribution to the recipient; and + +(b) You may distribute such Executable Form under the terms of this + License, or sublicense it under different terms, provided that the + license for the Executable Form does not attempt to limit or alter + the recipients' rights in the Source Code Form under this License. + +3.3. Distribution of a Larger Work + +You may create and distribute a Larger Work under terms of Your choice, +provided that You also comply with the requirements of this License for +the Covered Software. If the Larger Work is a combination of Covered +Software with a work governed by one or more Secondary Licenses, and the +Covered Software is not Incompatible With Secondary Licenses, this +License permits You to additionally distribute such Covered Software +under the terms of such Secondary License(s), so that the recipient of +the Larger Work may, at their option, further distribute the Covered +Software under the terms of either this License or such Secondary +License(s). + +3.4. Notices + +You may not remove or alter the substance of any license notices +(including copyright notices, patent notices, disclaimers of warranty, +or limitations of liability) contained within the Source Code Form of +the Covered Software, except that You may alter any license notices to +the extent required to remedy known factual inaccuracies. + +3.5. Application of Additional Terms + +You may choose to offer, and to charge a fee for, warranty, support, +indemnity or liability obligations to one or more recipients of Covered +Software. However, You may do so only on Your own behalf, and not on +behalf of any Contributor. You must make it absolutely clear that any +such warranty, support, indemnity, or liability obligation is offered by +You alone, and You hereby agree to indemnify every Contributor for any +liability incurred by such Contributor as a result of warranty, support, +indemnity or liability terms You offer. You may include additional +disclaimers of warranty and limitations of liability specific to any +jurisdiction. + +4. Inability to Comply Due to Statute or Regulation +--------------------------------------------------- + +If it is impossible for You to comply with any of the terms of this +License with respect to some or all of the Covered Software due to +statute, judicial order, or regulation then You must: (a) comply with +the terms of this License to the maximum extent possible; and (b) +describe the limitations and the code they affect. Such description must +be placed in a text file included with all distributions of the Covered +Software under this License. Except to the extent prohibited by statute +or regulation, such description must be sufficiently detailed for a +recipient of ordinary skill to be able to understand it. + +5. Termination +-------------- + +5.1. The rights granted under this License will terminate automatically +if You fail to comply with any of its terms. However, if You become +compliant, then the rights granted under this License from a particular +Contributor are reinstated (a) provisionally, unless and until such +Contributor explicitly and finally terminates Your grants, and (b) on an +ongoing basis, if such Contributor fails to notify You of the +non-compliance by some reasonable means prior to 60 days after You have +come back into compliance. Moreover, Your grants from a particular +Contributor are reinstated on an ongoing basis if such Contributor +notifies You of the non-compliance by some reasonable means, this is the +first time You have received notice of non-compliance with this License +from such Contributor, and You become compliant prior to 30 days after +Your receipt of the notice. + +5.2. If You initiate litigation against any entity by asserting a patent +infringement claim (excluding declaratory judgment actions, +counter-claims, and cross-claims) alleging that a Contributor Version +directly or indirectly infringes any patent, then the rights granted to +You by any and all Contributors for the Covered Software under Section +2.1 of this License shall terminate. + +5.3. In the event of termination under Sections 5.1 or 5.2 above, all +end user license agreements (excluding distributors and resellers) which +have been validly granted by You or Your distributors under this License +prior to termination shall survive termination. + +************************************************************************ +* * +* 6. Disclaimer of Warranty * +* ------------------------- * +* * +* Covered Software is provided under this License on an "as is" * +* basis, without warranty of any kind, either expressed, implied, or * +* statutory, including, without limitation, warranties that the * +* Covered Software is free of defects, merchantable, fit for a * +* particular purpose or non-infringing. The entire risk as to the * +* quality and performance of the Covered Software is with You. * +* Should any Covered Software prove defective in any respect, You * +* (not any Contributor) assume the cost of any necessary servicing, * +* repair, or correction. This disclaimer of warranty constitutes an * +* essential part of this License. No use of any Covered Software is * +* authorized under this License except under this disclaimer. * +* * +************************************************************************ + +************************************************************************ +* * +* 7. Limitation of Liability * +* -------------------------- * +* * +* Under no circumstances and under no legal theory, whether tort * +* (including negligence), contract, or otherwise, shall any * +* Contributor, or anyone who distributes Covered Software as * +* permitted above, be liable to You for any direct, indirect, * +* special, incidental, or consequential damages of any character * +* including, without limitation, damages for lost profits, loss of * +* goodwill, work stoppage, computer failure or malfunction, or any * +* and all other commercial damages or losses, even if such party * +* shall have been informed of the possibility of such damages. This * +* limitation of liability shall not apply to liability for death or * +* personal injury resulting from such party's negligence to the * +* extent applicable law prohibits such limitation. Some * +* jurisdictions do not allow the exclusion or limitation of * +* incidental or consequential damages, so this exclusion and * +* limitation may not apply to You. * +* * +************************************************************************ + +8. Litigation +------------- + +Any litigation relating to this License may be brought only in the +courts of a jurisdiction where the defendant maintains its principal +place of business and such litigation shall be governed by laws of that +jurisdiction, without reference to its conflict-of-law provisions. +Nothing in this Section shall prevent a party's ability to bring +cross-claims or counter-claims. + +9. Miscellaneous +---------------- + +This License represents the complete agreement concerning the subject +matter hereof. If any provision of this License is held to be +unenforceable, such provision shall be reformed only to the extent +necessary to make it enforceable. Any law or regulation which provides +that the language of a contract shall be construed against the drafter +shall not be used to construe this License against a Contributor. + +10. Versions of the License +--------------------------- + +10.1. New Versions + +Mozilla Foundation is the license steward. Except as provided in Section +10.3, no one other than the license steward has the right to modify or +publish new versions of this License. Each version will be given a +distinguishing version number. + +10.2. Effect of New Versions + +You may distribute the Covered Software under the terms of the version +of the License under which You originally received the Covered Software, +or under the terms of any subsequent version published by the license +steward. + +10.3. Modified Versions + +If you create software not governed by this License, and you want to +create a new license for such software, you may create and use a +modified version of this License if you rename the license and remove +any references to the name of the license steward (except to note that +such modified license differs from this License). + +10.4. Distributing Source Code Form that is Incompatible With Secondary +Licenses + +If You choose to distribute Source Code Form that is Incompatible With +Secondary Licenses under the terms of this version of the License, the +notice described in Exhibit B of this License must be attached. + +Exhibit A - Source Code Form License Notice +------------------------------------------- + + This Source Code Form is subject to the terms of the Mozilla Public + License, v. 2.0. If a copy of the MPL was not distributed with this + file, You can obtain one at http://mozilla.org/MPL/2.0/. + +If it is not possible or desirable to put the notice in a particular +file, then You may include the notice in a location (such as a LICENSE +file in a relevant directory) where a recipient would be likely to look +for such a notice. + +You may add additional accurate notices of copyright ownership. + +Exhibit B - "Incompatible With Secondary Licenses" Notice +--------------------------------------------------------- + + This Source Code Form is "Incompatible With Secondary Licenses", as + defined by the Mozilla Public License, v. 2.0. diff --git a/Readme.md b/Readme.md new file mode 100644 --- /dev/null +++ b/Readme.md @@ -0,0 +1,54 @@ +# Library for caching values. + +The library allows to cache result of an asynchronous computation for +no longer than a given period of time. + +# How to use + +In order to use the package you should add the package to the dependency +section of the cabal file of your package. + +In order to use the cache you should create a 'Handle' + +```haskell +{-# LANGUAGE ImportQualifiedPost #-} +{-# LANGUAGE NumericUnderscores #-} +{-# LANGUAGE BlockArguments #-} +import Control.Concurrent + +import System.Cache qualified as Cache +import System.Cache.Impl.Ghc qualified as Cache.Ghc +import System.Clock.Seconds + +main :: IO () +main = do + cache <- Cache.Ghc.new do + Cache.mkConfig 60 Monotonic + -- we create a cached version of computation + -- in order to hide implementation + let cachedTimeout input = Cache.requestOr cache input \i -> do + threadDelay $ i * 1_000_000 + pure i + -- We use our cached function + print (cachedTimeout 1) + print (cachedTimeout 1) + print (cachedTimeout 2) +``` + +``` +sh-3.2$ runhaskell local.hs | ts -S +00:00:03 2 +00:00:03 2 +00:00:06 3 +``` + +When running the program first we wait for 2 seconds, the next call returns immediately. +The third one is long as it uses a new input value. + + +# Developing the package + +``` +cabal configure +cabal build +``` diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,2 @@ +import Distribution.Simple +main = defaultMain diff --git a/lazy-cache.cabal b/lazy-cache.cabal new file mode 100644 --- /dev/null +++ b/lazy-cache.cabal @@ -0,0 +1,99 @@ +cabal-version: >=1.10 +name: lazy-cache +synopsis: Library for caching IO action that leverages on GHC RTS implementation +version: 0.2.0.0 +author: Alexander Vershilov +maintainer: backend-dev@sirius.online +copyright: 2019-2022 (C) Фонд "Талант и Успех" +license: MPL-2.0 +license-file: LICENSE +build-type: Simple +category: System +description: The library provides an interface for caching the results of IO actions. + This library relies on a blackholing — mechanism that is used to implement lazy + evaluation for avoiding concurrent runs of the action + (this is where the name of the library comes from). + . + The library provides caching mechanismsl with the following properties: + . + 1. when the function is called the successful result is cached by no more than a provided time; + 2. if the function ends with an exception, it will be rethrown, and the result will not be cached; + 3. if the function will be called with the same input value it immediately gets cached + result; + 4. if functions are called concurrently with the different input values they will not + block each other; + 5. if functions will be called concurrently with the same argument then only one will + act, others will wait until the first one is finished and will either return the + result once it's received, or will rethrow an exception if the first one + exits with an exception; + 6. outdated values are cleared only on accesses to the cache, so if no action is called + the data will not be cleared. + . + The main entry point of the library is "System.Cache" module, it explains how to + use the library and provides the public API, that does not depend on the actual + store implementation. + . + The library provides an interface for caching, and three implementations: + . + 1. "System.Cache.Impl.Ghc" — the main one based on GHC system; + + 2. "System.Cache.Impl.MVar" — implementation based on library functions; + + 3. "System.Cache.Impl.NoCache" — implementation that disables caching, but keeps the same interface + . + If you want to implement your own caching mechanism, or use internal API, you + can refer to the "System.Cache.Internal.Interface" module for an additional documentation. +extra-source-files: + CHANGELOG.md + Readme.md + +tested-with: + GHC == 9.2.2 + || == 8.10.7 + +source-repository head + type: git + location: https://github.com/cheopslab/lazy-cache + +library + exposed-modules: + System.Cache + System.Cache.Impl.Ghc + System.Cache.Impl.MVar + System.Cache.Impl.NoCache + System.Cache.Internal.Interface + other-extensions: + RecursiveDo + TemplateHaskell + build-depends: + base >=4.12 && <5, + hashable >=1.1.2.3 && <1.5, + psqueues >=0.2 && <0.3, + clock >= 0.8 + hs-source-dirs: src + ghc-options: -Wall + default-language: Haskell2010 + default-extensions: + LambdaCase + NumericUnderscores + OverloadedStrings + RecordWildCards + ScopedTypeVariables + +test-suite spec + type: exitcode-stdio-1.0 + main-is: Spec.hs + other-modules: + Cheops.Cache.CacheSpec + hs-source-dirs: + test + ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N + build-tool-depends: hspec-discover:hspec-discover + build-depends: + HUnit + , base >=4.7 && <5 + , lazy-cache + , hashable + , hspec + , clock + default-language: Haskell2010 diff --git a/src/System/Cache.hs b/src/System/Cache.hs new file mode 100644 --- /dev/null +++ b/src/System/Cache.hs @@ -0,0 +1,150 @@ +{-# LANGUAGE RecursiveDo #-} +{-# LANGUAGE TemplateHaskell #-} +-- | +-- General interface for the cache. This module is intended to be used +-- in th user code. +-- +-- __TLDR__ +-- +-- @ +-- {-# LANGUAGE ImportQualifiedPost #-} +-- {-# LANGUAGE NumericUnderscores #-} +-- {-# LANGUAGE BlockArguments #-} +-- import Control.Concurrent +-- +-- import "System.Cache" qualified as Cache +-- import "System.Cache.Impl.Ghc" qualified as Cache.Ghc +-- import System.Clock.Seconds +-- +-- main :: IO () +-- main = do +-- -- we create a new cache handle that acts as a storage for +-- -- cached values +-- cache <- Cache.Ghc.'System.Cache.Impl.Ghc.new' do +-- Cache.'System.Cache.mkConfig' 60 'System.Clock.Seconds.MonotonicCoarse' +-- -- we create a cached version of computation +-- -- in order to hide implementation +-- let cachedTimeout = Cache.'System.Cache.mkCached' @cache@ \i -> do +-- threadDelay $ i * 1_000_000 +-- pure i +-- -- We use our cached function +-- print (cachedTimeout 1) +-- @ +-- +module System.Cache + ( -- * API + -- ** Create + -- $api1 + Handle + -- $api2 + , Config + , mkConfig + -- ** Use + -- $api3 + , requestOr + -- $api4 + , cacheIO + -- * Helpers + -- $helpers + , new + , mkCached + ) where + +import Data.Functor +import Data.Hashable +import System.Clock.Seconds + +import System.Cache.Internal.Interface +import qualified System.Cache.Impl.Ghc as Ghc +import qualified System.Cache.Impl.MVar as MVar +import System.Environment +import System.IO.Unsafe + +-- $api1 +-- +-- In order to use this library you first need to explicitly create a storage +-- for the values. This storage is implemented by the abstract type 'Handle' that +-- provides only a public function interface but hides an actual implementation. +-- You can find full description of the 'Handle' in the "System.Cache.Internal.Interface" +-- module. + +-- $api2 +-- +-- In order to create a 'Handle' you'll need to call appropiate function from the +-- @System.Cache.Impl.\*.new@ module. This way you can chose an actual implementation. +-- Alternatively you can use 'System.Cache.new' function that will make a choise for you, or +-- create your own implementation. +-- +-- Each of those functions take a 'Config' as a parameter + +-- $api3 +-- +-- Once the storage is created you can use it for caching values via 'requestOr' method. + +-- $api4 +-- +-- The API of the method is not safe enough because you can for example ignore input +-- value in the funciton, or pass different function in different invocations with the +-- same storage. One the one hand we do not want to prevent such usages as may be done +-- for a purpose, but in order to provide additional safety we provide more safe methods: + +-- | Helper to create a config. +mkConfig + :: Int -- ^ Max time that the value can be cached (in seconds). + -> Clock -- ^ Type of the clock that the cache will use. + -> Config +mkConfig n clock = Config + { configLongestAge = fromNanoSecs (fromIntegral n * 1_000_000_000) + , configClock = clock + } + + +-- | Perform a request. +requestOr + :: Handle a b + -> a -- ^ Input parameters + -> (a -> IO b) -- ^ Function to cache. + -> IO b -- ^ Result. +requestOr Handle {..} k f = do + tm <- getClockTime + requestOrInternal tm k f + +-- | Wraps an IO action and returns a cached version of that method. +cacheIO + :: Handle a b -- ^ Values storage + -> (a -> IO b) -- ^ Action to cache + -> (a -> IO b) -- ^ A version that caches the result +cacheIO handle f = \k -> requestOr handle k f + +-- | Set default cache implementation. This method perfers to use +-- "System.Cache.Impl.Ghc" implementation unless @GHC_CACHE_IMPL@ environment value +-- has value @MVAR@ in this case "System.Cache.Impl.MVar" is used. +-- +-- This method is useful as a default one because it prefers a faster and stabler +-- implementation, but in case of emergency it allows to switch to the conservative +-- implementation without program recompilation. +-- +-- __N.B.__ this methos uses 'unsafePerformIO'. +new + :: (Show a, Hashable a, Ord a) + => Config + -> IO (Handle a b) +{-# NOINLINE new #-} +new = unsafePerformIO $ do + lookupEnv "GHC_CACHE_IMPL" >>= \case + Just "MVAR" -> pure $ MVar.new + _ -> pure $ Ghc.new + +-- | Wrapper for creatio cached values. This wrapper does not expose raw 'Handle', +-- so it will not be possible to unexpectedly reuse between different methods. +-- +-- @ +-- cachedIO <- 'mkCached' 'System.Cache.Impl.Ghc.new' config io +-- @ +mkCached + :: (Config -> IO (Handle a b)) -- ^ Create handle function + -> Config -- ^ Config for caching + -> (a -> IO b) -- ^ Action to cache + -> IO (a -> IO b) -- ^ Version that caches the result +mkCached mk config f = + mk config <&> \handle -> cacheIO handle f diff --git a/src/System/Cache/Impl/Ghc.hs b/src/System/Cache/Impl/Ghc.hs new file mode 100644 --- /dev/null +++ b/src/System/Cache/Impl/Ghc.hs @@ -0,0 +1,86 @@ +{-# LANGUAGE RecursiveDo #-} +-- | Caching based on the GHC heap object properties and relies on lazyness implementation +-- in the GHC RTS. This approach does it's best effort for avoiding the duplicated work, +-- however it the pathological cases it's possible that two theads will run the computation +-- on the same input concurrently. We have not observed this case in practice, but in the +-- case if you need strict guarantees on this property you should use "System.Cache.Impl.MVar" +-- instead. +-- +-- This is battle-tested implementation. That fits all the properties that are required by the +-- interface. +-- +module System.Cache.Impl.Ghc + ( new + ) where + +import Control.Exception +import Data.Hashable +import Data.HashPSQ as PSQ +import Data.IORef +import Data.Tuple +import Control.Monad +import System.Clock.Seconds + +import System.Cache.Internal.Interface + +-- | We need our internal values to be even more lazy, in order +-- to prevent early evaluation and deadlock. +data Lazy a = Lazy { getLazy :: a} + +-- | Creates new cache Handle. Keeps priotity queue from @psqueues@ package inside. +-- +-- Properties: +-- +-- * if multiple threads are running an IO action with the same input +-- concurrently then only one (with the best effort) will run, all +-- the rest will wait for that action and will either return a value, +-- or throw an exception depending on the the result of the first one +-- * storage is cleared only during access, it will remove redundant work +-- but may lead to the situation when cached values are stored in memory +-- for a longer period that it was expected +-- * psqueue structure uses both 'Hashable' and 'Ord' constraints and is +-- not vulnerable to the hash collision attacks. +-- +new + :: (Show a, Hashable a, Ord a) + => Config + -> IO (Handle a b) +new Config {..} = do + ref <- newIORef PSQ.empty + pure $ Handle + { requestOrInternal = \tm k f -> mdo + mbox <- + atomicModifyIORef ref + $ swap + . PSQ.alter + (\case + Just (p, ~v) | p >= diffTimeSpec tm configLongestAge -> + (Just v, Just (p, v)) + _ -> (Nothing, Just (tm, Lazy eresult)) + ) + k + eresult <- try $ maybe + (f k) + (\r -> do + evaluate (getLazy r) >>= \case + Left s -> throwIO s + Right x -> pure x + ) + mbox + result <- case eresult of + Left (s::SomeException) -> do + atomicModifyIORef' ref $ \v -> (PSQ.delete k v, ()) + throwIO s + Right x -> pure x + atomicModifyIORef' ref $ swap . PSQ.alterMin + (\case + Nothing -> ((), Nothing) + Just (kk, p, v) + | p < diffTimeSpec tm configLongestAge -> ((), Nothing) + | otherwise -> ((), Just (kk, p, v)) + ) + pure result + , remove = \k -> do + void $ atomicModifyIORef ref $ swap . PSQ.alter (const ((), Nothing)) k + , getClockTime = getTime configClock + } diff --git a/src/System/Cache/Impl/MVar.hs b/src/System/Cache/Impl/MVar.hs new file mode 100644 --- /dev/null +++ b/src/System/Cache/Impl/MVar.hs @@ -0,0 +1,118 @@ +-- | Safer cache version that is implemented totally +-- on the user level. Using 'MVar' as a synchronization +-- primitive. +-- +-- While this implementation is slower in general case it may +-- be more resilient to changes in GHC and RTS. This implementation +-- is mostly used in order to sanity check the GHC one, and in order +-- to be able to switch to this one without program recompilation. +-- +-- However if you need strict guarantees that the only one action with +-- the same input is run concurrently you should prefer this implementation. +module System.Cache.Impl.MVar + ( new + ) where + +import Control.Concurrent +import Control.Exception +import Control.Monad +import Data.HashPSQ as PSQ +import Data.Hashable +import Data.IORef +import Data.Tuple +import System.Clock.Seconds + +import System.Cache.Internal.Interface + +-- | Create new cache handle. Keeps priority queue from psqueues package inside. +-- +-- Properties: +-- +-- * if multiple threads are running an IO action with the same input +-- concurrently then only one will run, all the rest will wait for that +-- action and will either return a value, or throw an exception depending +-- on the the result of the first one +-- * storage is cleared only during access, it will remove redundant work +-- but may lead to the situation when cached values are stored in memory +-- for a longer period that it was expected +-- * psqueue structure uses both 'Hashable' and 'Ord' constraints and is +-- not vulnerable to the hash collision attacks. +-- +new + :: (Show a, Hashable a, Ord a) + => Config + -> IO (Handle a b) +new cfg@Config {..} = do + ref <- newIORef PSQ.empty + pure $ Handle + { requestOrInternal = \tm k f -> do + queue <- readIORef ref + result + <- case PSQ.lookup k queue of + Nothing -> insertElement cfg ref tm k f + Just (p, (r, lock)) -> do + readIORef r >>= \case + Nothing + -> updateLock cfg ref lock r tm k f + Just v + | p >= tm - configLongestAge -> pure v + | otherwise -> updateLock cfg ref lock r tm k f + atomicModifyIORef' ref $ swap . PSQ.alterMin + (\case + Nothing -> ((), Nothing) + Just (kk, p, v) + | p < tm - configLongestAge -> ((), Nothing) + | otherwise -> ((), Just (kk, p, v)) + ) + pure result + , remove = \k -> do + void $ atomicModifyIORef ref $ swap . PSQ.alter (const ((), Nothing)) k + , getClockTime = getTime configClock + } + +-- | There is no value in the queue, but someone may already trying to create a lock, +-- so we need to register a lock, verifying that it was registered concurrently. +insertElement :: (Hashable k, Ord k) + => Config + -> IORef (HashPSQ k Seconds (IORef (Maybe z), MVar (Maybe (Seconds, z)))) + -> Seconds + -> k + -> (k -> IO z) + -> IO z +insertElement cfg ref tm k f = newEmptyMVar >>= \x -> go x `onException` (tryPutMVar x Nothing) where + go our_lock = do + result_box <- newIORef Nothing + update_result + <- atomicModifyIORef ref $ swap . + PSQ.alter + (\case + Just x@(_, their_lock) -> (Just their_lock, Just x) + Nothing -> (Nothing, Just (tm, (result_box, our_lock))) + ) k + case update_result of + Just (r, their_lock) + -> updateLock cfg ref their_lock r tm k f -- Someone else managed to insert the lock, first. + Nothing -> do + -- We are holding a lock, so we need to evaluate value and register it + value <- f k + putMVar our_lock (Just (tm, value)) + writeIORef result_box (Just value) + pure value + +updateLock :: (Hashable k, Ord k) + => Config + -> IORef (HashPSQ k Seconds (IORef (Maybe z), MVar (Maybe (Seconds, z)))) + -> MVar (Maybe (Seconds, z)) + -> IORef (Maybe z) + -> Seconds + -> k + -> (k -> IO z) + -> IO z +updateLock Config{..} ref lock inner tm k f = modifyMVar lock $ \case + Just x@(p, v) -- Result exists and is valid, we can just return it + | p >= tm - configLongestAge -> pure (Just x, v) + _ -> do -- There is no result or it's outdated, we can update it. + value <- f k + writeIORef inner (Just value) + atomicModifyIORef ref (\queue -> (PSQ.insert k tm (inner,lock) queue, ())) + pure (Just (tm, value), value) diff --git a/src/System/Cache/Impl/NoCache.hs b/src/System/Cache/Impl/NoCache.hs new file mode 100644 --- /dev/null +++ b/src/System/Cache/Impl/NoCache.hs @@ -0,0 +1,20 @@ +{-# LANGUAGE RecursiveDo #-} +-- | Implementation that provides no caching at all. +-- Can be useful in order to disable caching without changing +-- the code at the use sites. +module System.Cache.Impl.NoCache + ( new + ) where + +import System.Cache.Internal.Interface +import System.Clock.Seconds + +-- | Creates an implementation that does not cache anything. +-- All actions runs as-is without locking. +new :: Config -> IO (Handle a b) +new Config{..} = do + pure $ Handle + { requestOrInternal = \_ k f -> f k + , remove = \_ -> pure () + , getClockTime = getTime configClock + } diff --git a/src/System/Cache/Internal/Interface.hs b/src/System/Cache/Internal/Interface.hs new file mode 100644 --- /dev/null +++ b/src/System/Cache/Internal/Interface.hs @@ -0,0 +1,47 @@ +-- | +-- +-- Internal interface for the Cache handle. In general you are not interested in this +-- module and should use public API from the "System.Cache" instead, unless: +-- +-- 1. you need to implement your own handle, +-- 2. you need to use internal functions like 'remove', +-- 3. you need to provide your own 'getClockTime' implementation +-- +-- +module System.Cache.Internal.Interface + ( Handle(..) + , Config(..) + ) where + +import System.Clock.Seconds + +-- | The public interface for the cache values storage. +-- +-- A storage is expected to provide the following properties: +-- +-- 1. If the function return succesfully then the result should be cached for a time period, +-- All later calls should return the cached value. +-- 2. In case of the concurrent actions an implementation should be the best effort to avoid +-- reduntant calls +data Handle a b = Handle + { requestOrInternal :: Seconds -> a -> (a -> IO b) -> IO b + -- ^ runs an action @f@ that takes a parameter @a@ and stores successful + -- result for time no longer than @s@. + , remove :: a -> IO () + -- ^ removes the result cached for input @a@. + , getClockTime :: IO Seconds + -- ^ finds current time. + } + +-- | Configuration for 'Cache' +-- +-- See "System.Cache.Internal.Interface" for all details on the fields. +data Config = Config + { configLongestAge :: Seconds + -- ^ The time that the value can be kept in cache. + , configClock :: Clock + -- ^ Type of the clock that is used by cache, by changing this parameter you can + -- optimize your usage for the different use cases, see "System.Clock.Seconds" + -- documentation for explanation of the choises. + } + diff --git a/test/Cheops/Cache/CacheSpec.hs b/test/Cheops/Cache/CacheSpec.hs new file mode 100644 --- /dev/null +++ b/test/Cheops/Cache/CacheSpec.hs @@ -0,0 +1,64 @@ +{-# LANGUAGE RankNTypes #-} +{-# LANGUAGE RecordWildCards #-} +{-# LANGUAGE NumericUnderscores #-} +module Cheops.Cache.CacheSpec where + +import Control.Exception +import Data.IORef +import System.Clock.Seconds +import Data.Hashable +import Test.Hspec +import Test.HUnit.Base ((@=?)) + +import qualified System.Cache as Cache +import qualified System.Cache.Impl.Ghc as Ghc +import qualified System.Cache.Impl.MVar as MVar +import System.Cache.Internal.Interface as Cache + +spec :: Spec +spec = do + describe "GHC" $ inner (Ghc.new) + describe "MVar" $ inner (MVar.new) + +inner :: (forall a b . (Show a, Hashable a, Ord a) => Cache.Config -> IO (Cache.Handle a b)) -> Spec +inner new = describe "Cache service" $ do + let configClock = Monotonic + let configLongestAge = fromNanoSecs (100 * 1_000_000_000) + it "cache store values" $ do + ch <- new Cache.Config{..} + ir <- newIORef True + let + f _ = do + firstTime <- readIORef ir + if firstTime then writeIORef ir False >> pure 0 else pure 1 + ((0 :: Int) @=?) =<< Cache.requestOr ch () f + ((0 :: Int) @=?) =<< Cache.requestOr ch () f + it "honour input" $ do + ch <- new Cache.Config{..} + let f x = pure x + ((3 :: Int) @=?) =<< Cache.requestOr ch 3 f + ((4 :: Int) @=?) =<< Cache.requestOr ch 4 f + ((3 :: Int) @=?) =<< Cache.requestOr ch 3 f + it "drops caches" $ do + ch <- new Cache.Config{ configLongestAge = fromNanoSecs 0, ..} + ir <- newIORef True + let + f _ = do + firstTime <- readIORef ir + if firstTime then writeIORef ir False >> pure 0 else pure 1 + ((0 :: Int) @=?) + =<< Cache.requestOrInternal ch (fromNanoSecs (0)) () f + ((1 :: Int) @=?) + =<< Cache.requestOrInternal ch (fromNanoSecs (2 * 1_000_000_000)) () f + it "handles exceptions" $ do + ch <- new Cache.Config{..} :: IO (Cache.Handle Int Int) + ((Left (ErrorCall "foo")) @=?) =<< + either (\(ErrorCallWithLocation s _) -> Left (ErrorCall s)) Right + <$> try (Cache.requestOr ch (3::Int) (\_ -> error "foo")) + -- second call is still ok + ((Left (ErrorCall "bar")) @=?) =<< + either (\(ErrorCallWithLocation s _) -> Left (ErrorCall s)) Right + <$> try (Cache.requestOr ch (3::Int) (\_ -> error "bar")) + (Right 4 @=?) =<< + either (\(ErrorCallWithLocation s _) -> Left (ErrorCall s)) Right + <$> try (Cache.requestOr ch (3::Int) (\_ -> pure 4)) diff --git a/test/Spec.hs b/test/Spec.hs new file mode 100644 --- /dev/null +++ b/test/Spec.hs @@ -0,0 +1,1 @@ +{-# OPTIONS_GHC -F -pgmF hspec-discover #-}