atomic and persistent collections for thread safety #143

devcrocod · 2025-07-07T21:31:57Z

#117

Motivation and Context

Using atomic and persistent collections for thread safety and optimal performance. And to preserve the current API

How Has This Been Tested?

locally

Breaking Changes

No

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

There were several solutions to this problem:

using a mutex, but that would require changing the current functions to suspend, which was problematic for some functions and would introduce breaking changes
using internal ConcurrentMap from ktor, which is not recommended for use
using atomic and kotlinx-collections-immutable. However, kotlinx-collections-immutable is in alpha, which also introduces risks for usage

…stent collections for thread safety

Copilot

Pull Request Overview

This PR replaces mutable maps with atomic persistent collections to improve thread-safety while preserving the existing public API.

Swapped all handler, tool, prompt, resource, and root maps to AtomicRef<PersistentMap> and updated registration/removal to atomic operations.
Adjusted handler lookup in Protocol, Server, and Client to use the new backing fields.
Added kotlinx-atomicfu and kotlinx-collections-immutable dependencies.

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

File	Description
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt	Replaced mutable handler maps with `AtomicRef<PersistentMap>` and updated all accesses to atomic ops.
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt	Migrated `tools`, `prompts`, and `resources` maps to atomic persistent maps and updated logic.
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/client/Client.kt	Migrated `roots` map to an atomic persistent map and updated add/remove methods.
gradle/libs.versions.toml	Added versions and library entries for `atomicfu` and `kotlinx-collections-immutable`.

Comments suppressed due to low confidence (2)

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt:125

Consider adding unit or integration tests to verify concurrent modifications of request, notification, response, and progress handler maps under multithreaded scenarios.

    private val _requestHandlers: AtomicRef<PersistentMap<String, suspend (JSONRPCRequest, RequestHandlerExtra) -> RequestResult?>> =

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt:267

For bulk removal of keys, consider using a batch operation (e.g., current.minusAll(toolNames)) if available to reduce repeated map rebuilds.

            toolNames.fold(current) { map, name ->

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt

e5l

The change is fine, but the reasoning is not clear. Could you add a test or provide an example of why it is needed?

devcrocod · 2025-07-08T10:18:53Z

This was a user request: #117
These changes make interactions with internal maps thread-safe

With a MutableMap, we can get a ConcurrentModificationException when one thread is iterating over the map while another thread inserts or removes an entry

| Package | Type | Package file | Manager | Update | Change | |---|---|---|---|---|---| | [io.modelcontextprotocol:kotlin-sdk](https://github.com/modelcontextprotocol/kotlin-sdk) | dependencies | misk/gradle/libs.versions.toml | gradle | minor | `0.5.0` -> `0.6.0` | | [org.jetbrains.kotlinx:kotlinx-serialization-json](https://github.com/Kotlin/kotlinx.serialization) | dependencies | misk/gradle/libs.versions.toml | gradle | minor | `1.7.3` -> `1.9.0` | | [org.jetbrains.kotlinx:kotlinx-serialization-core](https://github.com/Kotlin/kotlinx.serialization) | dependencies | misk/gradle/libs.versions.toml | gradle | minor | `1.7.3` -> `1.9.0` | | [com.google.apis:google-api-services-storage](http://nexus.sonatype.org/oss-repository-hosting.html) ([source](http://svn.sonatype.org/spice/tags/oss-parent-7)) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `v1-rev20250718-2.0.0` -> `v1-rev20250814-2.0.0` | | [software.amazon.awssdk:sdk-core](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:sqs](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:regions](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:dynamodb-enhanced](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:dynamodb](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:aws-core](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:bom](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | | [software.amazon.awssdk:auth](https://aws.amazon.com/sdkforjava) | dependencies | misk/gradle/libs.versions.toml | gradle | patch | `2.32.23` -> `2.32.24` | --- ### Release Notes <details> <summary>modelcontextprotocol/kotlin-sdk (io.modelcontextprotocol:kotlin-sdk)</summary> ### [`v0.6.0`](https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.6.0) [Compare Source](modelcontextprotocol/kotlin-sdk@0.5.0...0.6.0) #### What's Changed - Update jreleaser to fix publication issue by [@e5l](https://github.com/e5l) in modelcontextprotocol/kotlin-sdk#91 - Disable configuration cache to fix jreleaser issue by [@e5l](https://github.com/e5l) in modelcontextprotocol/kotlin-sdk#92 - feat: Add audio type according to 2025-03-26 spec by [@SeanChinJunKai](https://github.com/SeanChinJunKai) in modelcontextprotocol/kotlin-sdk#68 - fix(client): serialize inputSchema as input\_schema by [@shiqicao](https://github.com/shiqicao) in modelcontextprotocol/kotlin-sdk#97 - fix(client) add encodeDefault for field with non spec default value by [@shiqicao](https://github.com/shiqicao) in modelcontextprotocol/kotlin-sdk#99 - Make McpJson public to allow flexible protocol development by [@parnurzeal](https://github.com/parnurzeal) in modelcontextprotocol/kotlin-sdk#103 - fix: apply `requestBuilder` headers when sending rpc messages by [@dead8309](https://github.com/dead8309) in modelcontextprotocol/kotlin-sdk#96 - fix: Remove [@SerialName](https://github.com/SerialName) annotation for inputSchema by [@adamglin0](https://github.com/adamglin0) in modelcontextprotocol/kotlin-sdk#105 - add ios and wasm targets by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#81 - Add dependabot by [@StefMa](https://github.com/StefMa) in modelcontextprotocol/kotlin-sdk#121 - Bump org.jetbrains.kotlinx:kotlinx-serialization-json from 1.7.3 to 1.8.1 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#127 - Bump io.github.oshai:kotlin-logging from 7.0.0 to 7.0.7 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#126 - Bump org.jetbrains.kotlinx.binary-compatibility-validator from 0.17.0 to 0.18.0 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#125 - update kotlin to 2.2.0 and ktor to 3.1.3 by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#120 - Add client roots addition/removal API and listRoots handler by [@ptitjes](https://github.com/ptitjes) in modelcontextprotocol/kotlin-sdk#118 - Bump org.slf4j:slf4j-simple from 2.0.16 to 2.0.17 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#131 - Bump org.jetbrains.kotlinx:kotlinx-serialization-json from 1.8.1 to 1.9.0 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#132 - Bump io.mockk:mockk from 1.13.13 to 1.14.4 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#133 - Remove fixed suffix /sse by [@adamglin0](https://github.com/adamglin0) in modelcontextprotocol/kotlin-sdk#108 - sse server does not process endpoint correctly when sse path is not a directory by [@shendaxia-sm](https://github.com/shendaxia-sm) in modelcontextprotocol/kotlin-sdk#43 - Add labels to dependabot configuration for Kotlin and GitHub Actions by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#135 - feat: add tool annotations according to 2025-03-26 spec by [@SeanChinJunKai](https://github.com/SeanChinJunKai) in modelcontextprotocol/kotlin-sdk#71 - Bump ktor from 3.1.3 to 3.2.1 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#140 - Bump gradle/actions from 4.0.0 to 4.4.1 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#122 - Bump org.jreleaser from 1.17.0 to 1.19.0 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#141 - refactor `SseClientTransport` by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#142 - atomic and persistent collections for thread safety by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#143 - Bump org.gradle.toolchains.foojay-resolver-convention from 0.8.0 to 1.0.0 by [@dependabot](https://github.com/dependabot)\[bot] in modelcontextprotocol/kotlin-sdk#130 - Add support for elicitation by [@ptitjes](https://github.com/ptitjes) in modelcontextprotocol/kotlin-sdk#138 - Add support for tool structured content and output schema by [@ptitjes](https://github.com/ptitjes) in modelcontextprotocol/kotlin-sdk#146 - Add streamable http client transport by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#147 - Refactor JSON processing to exclude "method" in serialization by [@devcrocod](https://github.com/devcrocod) in [#157](modelcontextprotocol/kotlin-sdk#157) - Release 0.6.0 by [@devcrocod](https://github.com/devcrocod) in modelcontextprotocol/kotlin-sdk#149 #### New Contributors - [@shiqicao](https://github.com/shiqicao) made their first contribution in modelcontextprotocol/kotlin-sdk#97 - [@parnurzeal](https://github.com/parnurzeal) made their first contribution in modelcontextprotocol/kotlin-sdk#103 - [@dead8309](https://github.com/dead8309) made their first contribution in modelcontextprotocol/kotlin-sdk#96 - [@adamglin0](https://github.com/adamglin0) made their first contribution in modelcontextprotocol/kotlin-sdk#105 - [@StefMa](https://github.com/StefMa) made their first contribution in modelcontextprotocol/kotlin-sdk#121 - [@dependabot](https://github.com/dependabot)\[bot] made their first contribution in modelcontextprotocol/kotlin-sdk#127 - [@ptitjes](https://github.com/ptitjes) made their first contribution in modelcontextprotocol/kotlin-sdk#118 - [@shendaxia-sm](https://github.com/shendaxia-sm) made their first contribution in modelcontextprotocol/kotlin-sdk#43 **Full Changelog**: modelcontextprotocol/kotlin-sdk@0.5.0...0.6.0 </details> <details> <summary>Kotlin/kotlinx.serialization (org.jetbrains.kotlinx:kotlinx-serialization-json)</summary> ### [`v1.9.0`](https://github.com/Kotlin/kotlinx.serialization/blob/HEAD/CHANGELOG.md#190--2025-06-27) \================== This release updates Kotlin version to 2.2.0, includes several bugfixes and provides serializers for kotlin.time.Instant. #### Add kotlin.time.Instant serializers Instant class was moved from kotlinx-datetime library to Kotlin standard library. As a result, kotlinx-datetime 0.7.0 no longer has serializers for the Instant class. To use new kotlin.time.Instant class in your [@Serializable](https://github.com/Serializable) classes, you can use this 1.9.0 kotlinx-serialization version (Kotlin 2.2 is required). You can choose between default `InstantSerializer` which uses its string representation, or specify `InstantComponentSerializer` that represents instant as its components. See details in the [PR](Kotlin/kotlinx.serialization#2945). #### Other bugfixes - Fix resize in JsonPath ([#2995](Kotlin/kotlinx.serialization#2995)) - Fixed proguard rules for obfuscation to work correctly ([#2983](Kotlin/kotlinx.serialization#2983)) ### [`v1.8.1`](https://github.com/Kotlin/kotlinx.serialization/blob/HEAD/CHANGELOG.md#181--2025-03-31) \================== This release updates Kotlin version to 2.1.20, while also providing several important improvements and bugfixes. #### Improvements - Implemented encoding null in key and value of a map in Protobuf ([#2910](Kotlin/kotlinx.serialization#2910)) - Make type argument in JsonTransformingSerializer nullable ([#2911](Kotlin/kotlinx.serialization#2911)) - Use SPDX identifier in POMs ([#2936](Kotlin/kotlinx.serialization#2936)) (thanks to [Leon Linhart](https://github.com/TheMrMilchmann)) - Add watchosDeviceArm64 to Okio integration module ([#2920](Kotlin/kotlinx.serialization#2920)) (thanks to [Daniel Santiago](https://github.com/danysantiago)) - Update kotlinx-io version to 0.6.0 ([#2933](Kotlin/kotlinx.serialization#2933)) (thanks to [Piotr Krzemiński](https://github.com/krzema12)) #### Bugfixes - Fix incorrect enum coercion during deserialization from JsonElement ([#2962](Kotlin/kotlinx.serialization#2962)) - Supply proper equals(), hashCode(), and toString() for SerialDescriptor() wrapper ([#2942](Kotlin/kotlinx.serialization#2942)) - Do not encode empty packed collections in protobuf ([#2907](Kotlin/kotlinx.serialization#2907)) ### [`v1.8.0`](https://github.com/Kotlin/kotlinx.serialization/blob/HEAD/CHANGELOG.md#180--2025-01-06) \================== This release contains all of the changes from 1.8.0-RC. Kotlin 2.1.0 is used as a default, while upcoming 2.1.10 is also supported. Also added small bugfixes, including speedup of ProtoWireType.from ([#2879](Kotlin/kotlinx.serialization#2879)). </details> --- ### Configuration 📅 **Schedule**: Branch creation - "after 6pm every weekday,before 2am every weekday" in timezone Australia/Melbourne, Automerge - At any time (no schedule defined). 🚦 **Automerge**: Enabled. ♻ **Rebasing**: Never, or you tick the rebase/retry checkbox. 👻 **Immortal**: This PR will be recreated if closed unmerged. Get [config help](https://github.com/renovatebot/renovate/discussions) if that's undesired. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate). GitOrigin-RevId: 40e2f07ecd958e92e64c571d1351e91f96e71ce7

Refactor handlers and collections to use atomic references: use persi…

c5bf418

…stent collections for thread safety

devcrocod requested review from e5l and Copilot July 7, 2025 21:31

Copilot AI reviewed Jul 7, 2025

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src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt Outdated Show resolved Hide resolved

e5l requested changes Jul 8, 2025

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refactor remove and add public tools/roots/prompts for server

d84b342

Merge branch 'main' into devcrocod/thread-safety

d9caa40

e5l approved these changes Jul 9, 2025

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e5l enabled auto-merge (squash) July 9, 2025 06:39

e5l merged commit 2907252 into main Jul 9, 2025
2 of 3 checks passed

e5l deleted the devcrocod/thread-safety branch July 9, 2025 06:43

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atomic and persistent collections for thread safety #143

atomic and persistent collections for thread safety #143

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devcrocod commented Jul 7, 2025

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devcrocod commented Jul 8, 2025

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atomic and persistent collections for thread safety #143

atomic and persistent collections for thread safety #143

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devcrocod commented Jul 7, 2025

Motivation and Context

How Has This Been Tested?

Breaking Changes

Types of changes

Checklist

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devcrocod commented Jul 8, 2025

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