├── go.mod ├── go.sum ├── pkg ├── variable.go ├── context.go └── atomic.go ├── internal ├── clock.go └── lock.go ├── .gitignore ├── README.md └── LICENSE /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/kashmir 2 | 3 | go 1.13 4 | 5 | require github.com/pkg/errors v0.9.1 6 | -------------------------------------------------------------------------------- /go.sum: -------------------------------------------------------------------------------- 1 | github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4= 2 | github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0= 3 | -------------------------------------------------------------------------------- /pkg/variable.go: -------------------------------------------------------------------------------- 1 | package pkg 2 | 3 | import ( 4 | "github.com/kashmir/internal" 5 | "sync/atomic" 6 | ) 7 | 8 | type StmVariable struct { 9 | val atomic.Value 10 | lock internal.VersionedLock 11 | } 12 | 13 | func NewStmVariable(value interface{}) *StmVariable { 14 | stmVariable := &StmVariable{ 15 | val: atomic.Value{}, 16 | lock: 0, 17 | } 18 | stmVariable.val.Store(value) 19 | return stmVariable 20 | } 21 | -------------------------------------------------------------------------------- /internal/clock.go: -------------------------------------------------------------------------------- 1 | package internal 2 | 3 | import "sync/atomic" 4 | 5 | // VersionClock represents a global inter-transactional clock. 6 | type VersionClock uint64 7 | 8 | // Atomically increments clock and retrieves new value. 9 | func (vc *VersionClock) Increment() uint64 { 10 | return atomic.AddUint64((*uint64)(vc), 1) 11 | } 12 | 13 | // Atomically retrieves current clock value. 14 | func (vc *VersionClock) Load() uint64 { 15 | return atomic.LoadUint64((*uint64)(vc)) 16 | } 17 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | # Compiled Object files, Static and Dynamic libs (Shared Objects) 2 | *.o 3 | *.a 4 | *.so 5 | 6 | # Folders 7 | _obj 8 | _test 9 | 10 | # Architecture specific extensions/prefixes 11 | *.[568vq] 12 | [568vq].out 13 | 14 | *.cgo1.go 15 | *.cgo2.c 16 | _cgo_defun.c 17 | _cgo_gotypes.go 18 | _cgo_export.* 19 | 20 | _testmain.go 21 | 22 | # Vim files https://github.com/github/gitignore/blob/master/Global/Vim.gitignore 23 | # swap 24 | [._]*.s[a-w][a-z] 25 | [._]s[a-w][a-z] 26 | # session 27 | Session.vim 28 | # temporary 29 | .netrwhist 30 | *~ 31 | # auto-generated tag files 32 | tags 33 | 34 | *.exe 35 | cobra.test 36 | bin 37 | 38 | .idea/ 39 | *.iml 40 | -------------------------------------------------------------------------------- /pkg/context.go: -------------------------------------------------------------------------------- 1 | package pkg 2 | 3 | type StmContext struct { 4 | readLog map[*StmVariable]interface{} 5 | writeLog map[*StmVariable]interface{} 6 | restart bool 7 | readVersion uint64 8 | writeVersion uint64 9 | } 10 | 11 | func (sc *StmContext) Write(stmVariable *StmVariable, newVal interface{}) { 12 | sc.writeLog[stmVariable] = newVal 13 | } 14 | 15 | func (sc *StmContext) Read(stmVariable *StmVariable) interface{} { 16 | if newVal, foundInWriteLog := sc.writeLog[stmVariable]; foundInWriteLog { // Short road to success... 17 | return newVal 18 | } 19 | 20 | _, preReadVersion, _ := stmVariable.lock.Sample() 21 | readVal := stmVariable.val.Load() 22 | locked, postReadVersion, _ := stmVariable.lock.Sample() 23 | 24 | // Fail transaction if: 25 | // 1. Variable is currently being changed by some other goroutine; or if 26 | // 2. Variable was changed before/after being read; or if 27 | // 3. Variable is too new meaning our read version is outdated 28 | sc.restart = locked || preReadVersion != postReadVersion || preReadVersion > sc.readVersion 29 | 30 | return readVal 31 | } 32 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | ## Kashmir 2 | Transactional Locking II (TL2)-inspired STM library for Go, with a slight touch. 3 | On commit time, this library locks the read-set in addition to the write-set in order to prevent potential 4 | data races in the current TL2 algorithm. 5 | 6 | See: https://www.talhoffman.com/software-transactional-memory/ 7 | 8 | ### Example 9 | An example for solving the ATM problem of lack of composability: 10 | ```golang 11 | func main() { 12 | accountA := pkg.NewStmVariable(100) 13 | accountB := pkg.NewStmVariable(0) 14 | 15 | // Transfer 20 from Alice's account to Bob's one. 16 | transfer := func(ctx *pkg.StmContext) interface{} { 17 | currA := ctx.Read(accountA).(int) 18 | currB := ctx.Read(accountB).(int) 19 | 20 | ctx.Write(accountA, currA-20) 21 | ctx.Write(accountB, currB+20) 22 | 23 | return nil 24 | } 25 | pkg.StmAtomic(transfer) 26 | 27 | // Check the balance of accounts of Alice and Bob. 28 | inquiries := func(ctx *pkg.StmContext) interface{} { 29 | balance := make(map[*pkg.StmVariable]int) 30 | balance[accountA] = ctx.Read(accountA).(int) 31 | balance[accountB] = ctx.Read(accountB).(int) 32 | return balance 33 | } 34 | balance := pkg.StmAtomic(inquiries).(map[*pkg.StmVariable]int) 35 | fmt.Printf("The account of Alice holds %v.\nThe account of Bob holds %v.", 36 | balance[accountA], balance[accountB]) 37 | } 38 | ``` 39 | 40 | ### Caveats 41 | Please be careful when dealing with pointers (including channels, maps, and slices!) and 42 | use STM variables instead. 43 | 44 | In addition, Golang's type system forces us to use `interface{}` and type assertions. 45 | 46 | ### Contributions 47 | Contributions are always welcome! :heart: 48 | 49 | Feel free to open a Pull Request featuring improvements and fixes you see fit. 50 | 51 | ### License 52 | Unless otherwise noted, the Kashmir source files are distributed under the Apache Version 2.0 license found in the LICENSE file. 53 | -------------------------------------------------------------------------------- /internal/lock.go: -------------------------------------------------------------------------------- 1 | package internal 2 | 3 | import ( 4 | "github.com/pkg/errors" 5 | "sync/atomic" 6 | ) 7 | 8 | const versionOffset = 63 9 | 10 | var ( 11 | ErrLockModified = errors.New("lock has been modified") 12 | ErrAlreadyLocked = errors.New("lock is already locked") 13 | ErrAlreadyReleased = errors.New("lock is already released") 14 | ErrVersionOverflow = errors.New("version number cannot be larger than (2^63)-1") 15 | ) 16 | 17 | // VersionedLock consists of a lock bit and a version number. 18 | // Note that this lock doesn't enforce ownership! 19 | type VersionedLock uint64 20 | 21 | // Tries to acquire lock. 22 | // Non-blocking. 23 | func (vl *VersionedLock) TryAcquire() error { 24 | currentlyLocked, currentVersion, currentLock := vl.Sample() 25 | if currentlyLocked { 26 | return ErrAlreadyLocked 27 | } 28 | 29 | // Lock = true; Version = current 30 | return vl.tryCompareAndSwap(true, currentVersion, currentLock) 31 | } 32 | 33 | // Releases lock. 34 | func (vl *VersionedLock) Release() error { 35 | currentlyLocked, currentVersion, currentLock := vl.Sample() 36 | if !currentlyLocked { 37 | return ErrAlreadyReleased 38 | } 39 | 40 | // Lock = false; Version = current 41 | return vl.tryCompareAndSwap(false, currentVersion, currentLock) 42 | } 43 | 44 | // Atomically updates lock version and releases it. 45 | func (vl *VersionedLock) VersionedRelease(newVersion uint64) error { 46 | currentlyLocked, _, currentLock := vl.Sample() 47 | if !currentlyLocked { 48 | return ErrAlreadyReleased 49 | } 50 | 51 | // Lock = false; Version = new 52 | return vl.tryCompareAndSwap(false, newVersion, currentLock) 53 | } 54 | 55 | // Retrieves lock state - whether it is locked, its version, and its raw form. 56 | func (vl *VersionedLock) Sample() (bool, uint64, uint64) { 57 | current := atomic.LoadUint64((*uint64)(vl)) 58 | locked, version := vl.parse(current) 59 | return locked, version, current 60 | } 61 | 62 | func (vl *VersionedLock) tryCompareAndSwap(doLock bool, desiredVersion uint64, compareTo uint64) error { 63 | newLock, err := vl.serialize(doLock, desiredVersion) 64 | if err != nil { 65 | return errors.WithMessage(err, "try compare and swap") 66 | } 67 | 68 | if swapped := atomic.CompareAndSwapUint64((*uint64)(vl), compareTo, newLock); !swapped { 69 | return ErrLockModified 70 | } 71 | return nil 72 | } 73 | 74 | func (vl *VersionedLock) serialize(locked bool, version uint64) (uint64, error) { 75 | if (version >> versionOffset) == 1 { // Version mustn't override our lock bit. 76 | return 0, ErrVersionOverflow 77 | } 78 | 79 | if locked { 80 | return (1 << versionOffset) | version, nil 81 | } 82 | return version, nil 83 | } 84 | 85 | func (vl *VersionedLock) parse(serialized uint64) (bool, uint64) { 86 | version := (1<> versionOffset 88 | return lockedBit == 1, version 89 | } 90 | -------------------------------------------------------------------------------- /pkg/atomic.go: -------------------------------------------------------------------------------- 1 | package pkg 2 | 3 | import ( 4 | "github.com/kashmir/internal" 5 | "github.com/pkg/errors" 6 | ) 7 | 8 | var versionClock internal.VersionClock 9 | 10 | func StmAtomic(block func(*StmContext) interface{}) interface{} { 11 | for { 12 | ctx := &StmContext{ 13 | readLog: make(map[*StmVariable]interface{}, 0), 14 | writeLog: make(map[*StmVariable]interface{}, 0), 15 | restart: false, 16 | readVersion: versionClock.Load(), 17 | writeVersion: 0, 18 | } 19 | 20 | retVal := block(ctx) 21 | if ctx.restart { 22 | continue 23 | } 24 | 25 | // "And she's buying a stairway to heaven..." 26 | if len(ctx.writeLog) == 0 { 27 | return retVal 28 | } 29 | 30 | lockSet := make(map[*StmVariable]int, 0) 31 | if err := tryAcquireSets(ctx, lockSet); err != nil { 32 | if fatal := isFatalAcquireErr(err); fatal { // Avoid a panic if lock is already acquired. 33 | panic(fatal) 34 | } 35 | continue 36 | } 37 | 38 | ctx.writeVersion = versionClock.Increment() 39 | 40 | // Now that our read and write sets are locked, we need to ensure that nothing has changed in terms of our 41 | // read set, in-between running the user's code and locking everything. 42 | // However, if no other concurrent actors were involved (readVersion == writeVersion - 1), there is no need to 43 | // validate anything cause we were all alone. 44 | if ctx.readVersion != ctx.writeVersion-1 { 45 | if validated := validateReadSet(ctx, lockSet); !validated { 46 | continue 47 | } 48 | } 49 | 50 | commitTransaction(ctx, lockSet) 51 | 52 | return retVal 53 | } 54 | } 55 | 56 | func tryAcquireSets(ctx *StmContext, lockSet map[*StmVariable]int) error { 57 | for writeVar := range ctx.writeLog { 58 | if err := writeVar.lock.TryAcquire(); err != nil { 59 | releaseLockSet(lockSet) 60 | return errors.WithMessage(err, "try acquire write log") 61 | } 62 | 63 | lockSet[writeVar] = 1 64 | } 65 | 66 | for readVar := range ctx.readLog { 67 | // Avoid locking a variable which was already locked by us (either by previously being read 68 | // or by being part of the write log). 69 | if _, alreadyLocked := lockSet[readVar]; alreadyLocked { 70 | continue 71 | } 72 | 73 | if err := readVar.lock.TryAcquire(); err != nil { 74 | releaseLockSet(lockSet) 75 | return errors.WithMessage(err, "try acquire read log") 76 | } 77 | 78 | lockSet[readVar] = 1 79 | } 80 | return nil 81 | } 82 | 83 | func releaseLockSet(writeLockSet map[*StmVariable]int) { 84 | for alreadyLocked := range writeLockSet { 85 | if err := alreadyLocked.lock.Release(); err != nil { 86 | panic(err) 87 | } 88 | } 89 | } 90 | 91 | func validateReadSet(ctx *StmContext, lockSet map[*StmVariable]int) bool { 92 | for readVar := range ctx.readLog { 93 | locked, version, _ := readVar.lock.Sample() 94 | _, lockedByUs := lockSet[readVar] 95 | if (locked && !lockedByUs) || version > ctx.readVersion { 96 | return false 97 | } 98 | } 99 | 100 | return true 101 | } 102 | 103 | func commitTransaction(ctx *StmContext, lockSet map[*StmVariable]int) { 104 | releasedSet := make(map[*StmVariable]int, len(lockSet)) 105 | 106 | for writeVar, writeVal := range ctx.writeLog { 107 | oldVal := writeVar.val.Load() 108 | writeVar.val.Store(writeVal) 109 | 110 | if err := writeVar.lock.VersionedRelease(ctx.writeVersion); err != nil { 111 | writeVar.val.Store(oldVal) // Just in case a recover is used up the latter. 112 | panic(err) 113 | } 114 | 115 | releasedSet[writeVar] = 1 116 | } 117 | 118 | for readVar := range ctx.readLog { 119 | // Avoid releasing a variable which was already released by us (either by previously being read 120 | // or by being part of the write log). 121 | if _, alreadyReleased := releasedSet[readVar]; alreadyReleased { 122 | continue 123 | } 124 | 125 | if err := readVar.lock.Release(); err != nil { 126 | panic(err) 127 | } 128 | 129 | releasedSet[readVar] = 1 130 | } 131 | } 132 | 133 | func isFatalAcquireErr(err error) bool { 134 | switch errors.Cause(err) { 135 | case internal.ErrLockModified, internal.ErrVersionOverflow: 136 | return true 137 | default: 138 | return false 139 | } 140 | } 141 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | 2 | Apache License 3 | Version 2.0, January 2004 4 | http://www.apache.org/licenses/ 5 | 6 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 7 | 8 | 1. Definitions. 9 | 10 | "License" shall mean the terms and conditions for use, reproduction, 11 | and distribution as defined by Sections 1 through 9 of this document. 12 | 13 | "Licensor" shall mean the copyright owner or entity authorized by 14 | the copyright owner that is granting the License. 15 | 16 | "Legal Entity" shall mean the union of the acting entity and all 17 | other entities that control, are controlled by, or are under common 18 | control with that entity. For the purposes of this definition, 19 | "control" means (i) the power, direct or indirect, to cause the 20 | direction or management of such entity, whether by contract or 21 | otherwise, or (ii) ownership of fifty percent (50%) or more of the 22 | outstanding shares, or (iii) beneficial ownership of such entity. 23 | 24 | "You" (or "Your") shall mean an individual or Legal Entity 25 | exercising permissions granted by this License. 26 | 27 | "Source" form shall mean the preferred form for making modifications, 28 | including but not limited to software source code, documentation 29 | source, and configuration files. 30 | 31 | "Object" form shall mean any form resulting from mechanical 32 | transformation or translation of a Source form, including but 33 | not limited to compiled object code, generated documentation, 34 | and conversions to other media types. 35 | 36 | "Work" shall mean the work of authorship, whether in Source or 37 | Object form, made available under the License, as indicated by a 38 | copyright notice that is included in or attached to the work 39 | (an example is provided in the Appendix below). 40 | 41 | "Derivative Works" shall mean any work, whether in Source or Object 42 | form, that is based on (or derived from) the Work and for which the 43 | editorial revisions, annotations, elaborations, or other modifications 44 | represent, as a whole, an original work of authorship. For the purposes 45 | of this License, Derivative Works shall not include works that remain 46 | separable from, or merely link (or bind by name) to the interfaces of, 47 | the Work and Derivative Works thereof. 48 | 49 | "Contribution" shall mean any work of authorship, including 50 | the original version of the Work and any modifications or additions 51 | to that Work or Derivative Works thereof, that is intentionally 52 | submitted to Licensor for inclusion in the Work by the copyright owner 53 | or by an individual or Legal Entity authorized to submit on behalf of 54 | the copyright owner. For the purposes of this definition, "submitted" 55 | means any form of electronic, verbal, or written communication sent 56 | to the Licensor or its representatives, including but not limited to 57 | communication on electronic mailing lists, source code control systems, 58 | and issue tracking systems that are managed by, or on behalf of, the 59 | Licensor for the purpose of discussing and improving the Work, but 60 | excluding communication that is conspicuously marked or otherwise 61 | designated in writing by the copyright owner as "Not a Contribution." 62 | 63 | "Contributor" shall mean Licensor and any individual or Legal Entity 64 | on behalf of whom a Contribution has been received by Licensor and 65 | subsequently incorporated within the Work. 66 | 67 | 2. Grant of Copyright License. Subject to the terms and conditions of 68 | this License, each Contributor hereby grants to You a perpetual, 69 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 70 | copyright license to reproduce, prepare Derivative Works of, 71 | publicly display, publicly perform, sublicense, and distribute the 72 | Work and such Derivative Works in Source or Object form. 73 | 74 | 3. Grant of Patent License. Subject to the terms and conditions of 75 | this License, each Contributor hereby grants to You a perpetual, 76 | worldwide, non-exclusive, no-charge, royalty-free, irrevocable 77 | (except as stated in this section) patent license to make, have made, 78 | use, offer to sell, sell, import, and otherwise transfer the Work, 79 | where such license applies only to those patent claims licensable 80 | by such Contributor that are necessarily infringed by their 81 | Contribution(s) alone or by combination of their Contribution(s) 82 | with the Work to which such Contribution(s) was submitted. If You 83 | institute patent litigation against any entity (including a 84 | cross-claim or counterclaim in a lawsuit) alleging that the Work 85 | or a Contribution incorporated within the Work constitutes direct 86 | or contributory patent infringement, then any patent licenses 87 | granted to You under this License for that Work shall terminate 88 | as of the date such litigation is filed. 89 | 90 | 4. Redistribution. You may reproduce and distribute copies of the 91 | Work or Derivative Works thereof in any medium, with or without 92 | modifications, and in Source or Object form, provided that You 93 | meet the following conditions: 94 | 95 | (a) You must give any other recipients of the Work or 96 | Derivative Works a copy of this License; and 97 | 98 | (b) You must cause any modified files to carry prominent notices 99 | stating that You changed the files; and 100 | 101 | (c) You must retain, in the Source form of any Derivative Works 102 | that You distribute, all copyright, patent, trademark, and 103 | attribution notices from the Source form of the Work, 104 | excluding those notices that do not pertain to any part of 105 | the Derivative Works; and 106 | 107 | (d) If the Work includes a "NOTICE" text file as part of its 108 | distribution, then any Derivative Works that You distribute must 109 | include a readable copy of the attribution notices contained 110 | within such NOTICE file, excluding those notices that do not 111 | pertain to any part of the Derivative Works, in at least one 112 | of the following places: within a NOTICE text file distributed 113 | as part of the Derivative Works; within the Source form or 114 | documentation, if provided along with the Derivative Works; or, 115 | within a display generated by the Derivative Works, if and 116 | wherever such third-party notices normally appear. The contents 117 | of the NOTICE file are for informational purposes only and 118 | do not modify the License. You may add Your own attribution 119 | notices within Derivative Works that You distribute, alongside 120 | or as an addendum to the NOTICE text from the Work, provided 121 | that such additional attribution notices cannot be construed 122 | as modifying the License. 123 | 124 | You may add Your own copyright statement to Your modifications and 125 | may provide additional or different license terms and conditions 126 | for use, reproduction, or distribution of Your modifications, or 127 | for any such Derivative Works as a whole, provided Your use, 128 | reproduction, and distribution of the Work otherwise complies with 129 | the conditions stated in this License. 130 | 131 | 5. Submission of Contributions. Unless You explicitly state otherwise, 132 | any Contribution intentionally submitted for inclusion in the Work 133 | by You to the Licensor shall be under the terms and conditions of 134 | this License, without any additional terms or conditions. 135 | Notwithstanding the above, nothing herein shall supersede or modify 136 | the terms of any separate license agreement you may have executed 137 | with Licensor regarding such Contributions. 138 | 139 | 6. Trademarks. This License does not grant permission to use the trade 140 | names, trademarks, service marks, or product names of the Licensor, 141 | except as required for reasonable and customary use in describing the 142 | origin of the Work and reproducing the content of the NOTICE file. 143 | 144 | 7. Disclaimer of Warranty. Unless required by applicable law or 145 | agreed to in writing, Licensor provides the Work (and each 146 | Contributor provides its Contributions) on an "AS IS" BASIS, 147 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 148 | implied, including, without limitation, any warranties or conditions 149 | of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A 150 | PARTICULAR PURPOSE. You are solely responsible for determining the 151 | appropriateness of using or redistributing the Work and assume any 152 | risks associated with Your exercise of permissions under this License. 153 | 154 | 8. Limitation of Liability. In no event and under no legal theory, 155 | whether in tort (including negligence), contract, or otherwise, 156 | unless required by applicable law (such as deliberate and grossly 157 | negligent acts) or agreed to in writing, shall any Contributor be 158 | liable to You for damages, including any direct, indirect, special, 159 | incidental, or consequential damages of any character arising as a 160 | result of this License or out of the use or inability to use the 161 | Work (including but not limited to damages for loss of goodwill, 162 | work stoppage, computer failure or malfunction, or any and all 163 | other commercial damages or losses), even if such Contributor 164 | has been advised of the possibility of such damages. 165 | 166 | 9. Accepting Warranty or Additional Liability. While redistributing 167 | the Work or Derivative Works thereof, You may choose to offer, 168 | and charge a fee for, acceptance of support, warranty, indemnity, 169 | or other liability obligations and/or rights consistent with this 170 | License. However, in accepting such obligations, You may act only 171 | on Your own behalf and on Your sole responsibility, not on behalf 172 | of any other Contributor, and only if You agree to indemnify, 173 | defend, and hold each Contributor harmless for any liability 174 | incurred by, or claims asserted against, such Contributor by reason 175 | of your accepting any such warranty or additional liability. 176 | 177 | END OF TERMS AND CONDITIONS 178 | 179 | APPENDIX: How to apply the Apache License to your work. 180 | 181 | To apply the Apache License to your work, attach the following 182 | boilerplate notice, with the fields enclosed by brackets "[]" 183 | replaced with your own identifying information. (Don't include 184 | the brackets!) The text should be enclosed in the appropriate 185 | comment syntax for the file format. We also recommend that a 186 | file or class name and description of purpose be included on the 187 | same "printed page" as the copyright notice for easier 188 | identification within third-party archives. 189 | 190 | Copyright [yyyy] [name of copyright owner] 191 | 192 | Licensed under the Apache License, Version 2.0 (the "License"); 193 | you may not use this file except in compliance with the License. 194 | You may obtain a copy of the License at 195 | 196 | http://www.apache.org/licenses/LICENSE-2.0 197 | 198 | Unless required by applicable law or agreed to in writing, software 199 | distributed under the License is distributed on an "AS IS" BASIS, 200 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 201 | See the License for the specific language governing permissions and 202 | limitations under the License. 203 | --------------------------------------------------------------------------------