Golang concurrent map reads. May 1, 2021 · The new sync. You can read more about it in the ...

Golang concurrent map reads. May 1, 2021 · The new sync. You can read more about it in the golang repo, for example here and here Nov 3, 2023 · Different ways to protect maps from concurrent access in Golang. 先说问题 Golang的原生Map是不支持并发写的，但是可以并发读，是一种非 线程安全 的结构。以下程序直接报错: fatal error: concurrent map read and map write，即便访问的是不同的key。 Is the standard map thread-safe if all you do is read it? My program concurrently walks through the file system looking for files of specific file extensions. Mutex or a sync. Map {} or sync. Store method and report an error, read and write the sync. As long as all goroutines are only reading—looking up elements in the map, including iterating through it using a for range loop—and not changing the map by assigning to elements or doing deletions, it is safe for them to access the map concurrently without synchronization. For example, when a request occurs at the same time, they will be fatal error: concurrent map read and map write. Is it safe to write to a Golang map concurrently if the keys are always unique? Asked 8 years, 7 months ago Modified 2 years, 9 months ago Viewed 7k times For inserts, you'd add to the map and append to the slice, so that the slice remains sorted and the map always has all valid keys For expiration, you'd iterate the slice until you find an unexpired key, deleting each entry from the map. Do you remove elements from your map? Hi Gophers, I'm a newbie to Go, and I have a question regarding Go maps and concurrency. The stdlib sync. Mar 23, 2016 · Map is concurrent safe for read only in Golang. go#L542 Sep 2, 2016 · Go 1. Dec 2, 2018 · golang中map并发读写问题及解决方法 一、map并发读写问题 如果map由多协程同时读和写就会出现 fatal error:concurrent map read and map write的错误 如下代码很容易就出现map并发读写问题 func main () { c := make (map [string]int) go func () {//开一个协程写map for j := 0; j < 1000000; j++ { Jun 24, 2025 · 🚨 The Problem: Go Maps Are Not Concurrency-Safe Go’s native map type works great in single-threaded scenarios. Map is designed for concurrent scenarios. Mutex, but I haven't found an example that helped me understand how to use it in my specific situation. Map. Firstly, I have already read this How safe are Golang maps for concurrent Read/Write operations? and my question is not how safe golang maps are during read/write but a lot more specific. Jan 23, 2026 · Learn how to safely access maps from multiple goroutines in Go using mutexes, sync. If you could post more of your file, it would be easier to give a better answer. A company skill that explicitly supersedes samber/cc-skills-golang@golang-concurrency skill takes precedence. Jun 22, 2018 · some times, they will be fatal error: concurrent map read and map write. Use when writing or reviewing concurrent Go code. Map, Go’s concurrency superhero since 1. Map。 concurrent-map的优势 concurrent-map 提供了一种高性能的解决方案:通过对内部 map 进行分片，降低锁粒度，从而达到最少的锁等待时间 (锁冲突)。 Jan 2, 2017 · golang / go Public Notifications You must be signed in to change notification settings Fork 18. In Go, maps are not safe for concurrent use, meaning if one goroutine changes the contents of the map while another attempts to read from it, this can lead to runtime panics. The Root of Concurrent Map Write Issue Maps inherently encapsulate some complexity to provide fast and efficient access to data. Aug 9, 2017 · Golang fatal error: concurrent map read and map write Ask Question Asked 8 years, 7 months ago Modified 8 years, 7 months ago Aug 10, 2025 · Master Go concurrency with this comprehensive guide. map。 May 31, 2018 · Thread safe map storage for concurrent writing Getting Help digininja (Robin) May 31, 2018, 7:42am 1 Mar 6, 2026 · Map is like a Go map [any]any but is safe for concurrent use by multiple goroutines without additional locking or coordination. This is ideal for read-heavy applications, improving performance by reducing blocking during reads. Now your map has concurrent read/write. By checking the data, we found that before go 1. This guide covers the solutions. Sep 27, 2022 · Go语言中map非并发安全，官方FAQ及源码表明其通过标志位检测并发问题。测试显示并发读写会报错，可用sync. Feb 4, 2020 · Map access is unsafe only when updates are occurring. All the workers are reading from `inputCh` channel one by one. Contribute to lockp111/go-cmap development by creating an account on GitHub. Jul 1, 2019 · Go: Concurrency Access with Maps — Part III ℹ️ This article follows “Go: Map Design by Code” that describes the internal implementation of the map. This tutorial explores the fundamental techniques for map creation, handling concurrent access, and preventing potential data race conditions in Go. Making maps and slices thread safe Maps and slices are safe for concurrent reads, however concurrently reading/writing is not supported, and concurrent writes are not Feb 21, 2023 · concurrent-map concurrent-map 是Golang中一个流行的并发安全的哈希表库，它允许多个goroutine同时对哈希表进行读写操作，而不需要使用显式的锁或同步原语。 该库的核心原理是使用分片锁，将哈希表分成多个小的哈希表片段，并为每个片段分配一个独立的锁。 Mar 17, 2019 · If you are a golang web application developer, then you often might encounter a use case of storing some data in memory in a go map for frequent access. "I have read that I am suppose to use sync. map is concurrent Jun 24, 2016 · The range action itself should be performed in a concurrent-safe manner and if your map is changing it's likely that you'll get strange sequence of elements (every time you range over a map, the sequence of elements you get would be different. [23] The designers wanted to address criticisms of other languages in use at Google, but keep their useful characteristics: [24] Static typing and run-time efficiency (like C) Readability and usability (like Python) [25] High-performance networking and While Go has some really nice features making it so easy for developers to create concurrent applications, not all of the types in Go are safe for concurrent use. The new sync. May 7, 2021 · Go语言中map并发读写会导致panic，可通过加锁解决。使用sync. Reading and writing from multiple goroutines without synchronization causes race conditions and can crash your program. Jan 16, 2025 · Golang fatal error: concurrent map read and map write dictionary, go asked by user4283089 on 08:36AM - 09 Aug 17 UTC Aug 5, 2021 · When it comes to concurrency, every language does something differently. Map，确保多协程环境下数据安全。 Sep 22, 2025 · Golang - Data Structures - Concurrency with Maps Introduction A critical point to understand about Go’s built-in map type is that it is not safe for concurrent use. Map and native map + mutex/read-write lock. Map & ConcurrentMap 并发map,是指 多线程 安全的map数据结构, 我们知道go语言原生的map是不支持并发的, 要想获得一个并发map, 我们有如下的几种方案: map with mutex sync. atomic, sync. Map has a few key differences from this map. Mutex, sync. a thread-safe concurrent map for go. Ask questions and post articles about the Go programming language and related tools, events etc. That implies a write lock to complete the delete. An alternative would be to define the map inside the handler if you only need it there. Mar 28, 2021 · 引言 Go语言原生的 map 类型并不支持并发读写。 在Go 1. But if you try to read and write to a map from multiple goroutines without Jul 28, 2024 · Let us build a Thread safe ShardedMap in Golang A simple but useful concurrency implementation From this article, I will guide you through designing and developing a simple concurrent map in Oct 4, 2024 · Go’s sync. You could first lock it for reading only, and if the height manager already exists, you can return it. go#L118,会看到读的时候会检查hashWriting标志， 如果有这个标志，就会报并发错误。 写的时候会设置这个标志: hashmap. Map and Channels for concurrent map access for increments Nikolay Dimitrov 2 min read · Mar 1, 2021 · What happens in a concurrent scenario of map read/write operations? Until now, we had assumed that only one function can access and modify the map, so iteration is simple. However, what if this iteration needs to be done in multiple functions, or more specifically, multiple goroutines? Let’s take an example to investigate what’s happening. One challenging aspect of concurrency is safely handling shared data structures, particularly maps. I suspect because the code is not truly concurrent. 1. To handle such cases, you can use synchronization techniques to ensure safety when accessing shared resources across multiple threads (goroutines). Aug 2, 2022 · Go maps are only concurrent safe if all accesses are reads (lookups) after the map is initialized. RWMutex introduces a read/write bias: it allows multiple concurrent readers but only one writer at a time. fatal error: concurrent map Documentation The Go programming language is an open source project to make programmers more productive. Sep 26, 2018 · Now i have a map with only one write/delete goroutine and many read goroutines, there are some solutions upon Map with concurrent access, such as RWMutex, sync. 9, sync. It’s got some good tricks up its sleeve, like handling reads without locking, but it’s not always the best choice. Map` which supports ranging. Run Skill in Manus Jul 16, 2021 · I will show you how to safely write and read from maps in a concurrent environment in go. 6, concurrent reading and writing of map did not immediately report an error. Jan 21, 2024 · Introduced in Go 1. In this guide, I’ll break down why it rocks, where it shines, and how to dodge its kryptonite. Go compiles quickly to machine code yet has This is effective for low-scale use, but in high-concurrency scenarios, it can cause contention — each access blocks others, even reads. Learn essential Golang concurrency techniques for safely updating map values, covering mutex strategies, synchronization patterns, and best practices for thread-safe map operations in Go programming. In Go, concurrent modification of a map is not merely undefined behavior—it’s a ticking time bomb: Nov 26, 2021 · Because concurrent goroutines are used so commonly in Go, the standard library has a specialized data structure that acts like a normal map, but is perfectly safe to be read and written to across multiple goroutines without the use of an external mutex. Mar 26, 2018 · The easiest fix would be to use a Map from the package sync. Map 读写map分级 orcaman/concurrent-map 分片 Map built-in map本质是动态哈希算法实现,在运行过程中桶会分裂,导致 元素的迁移. 9中，引入了 sync. Introduction In the world of Golang programming, understanding how to create and manage maps safely is crucial for developing robust and efficient applications. Oct 27, 2022 · Closed 3 years ago. Map实现安全并发访问。 When trying to use this struct with multiple goroutines sometimes I get one of these errors: fatal error: concurrent map read and map write or concurrent map writes After reading the this thre Jul 10, 2018 · 简介： #冲突过程 异步对象序列化，对象里面如果有map，并且使用json. The good side of this is that multiple readers could access it simultaneously without blocking each other. Map is designed for append-only scenarios. 6 added a lightweight concurrent misuse of maps detection to the runtime: The runtime has added lightweight, best-effort detection of concurrent misuse of maps. It’s not just a band-aid—it’s a sleek, purpose-built tool for high-concurrency chaos. Map isn’t a magic bullet for all concurrent map needs. Aug 15, 2024 · 问题描述 在golang中，map是一种非常常用的数据结构。但是在并发环境下，map是不安全的，会出现并发问题。 Jun 15, 2024 · runtime: concurrent map access detection in hashmap. This article explores read-write synchronization techniques for maps in Go, starting from basic to more advanced patterns. ) Nov 14, 2019 · 错误信息是: fatal error: concurrent map read and map write。 如果你查看Go的源代码: hashmap_fast. Map, channels Concurrent map iteration can be a challenge in Golang due to the possibility of data races. Feb 16, 2025 · A look into how maps are implemented in Golang and how to ensure concurrent safety when working with maps. go only catches one stack #26703 runtime/race: document and fix "trap when race detected" #23577 runtime: crash while deleting all keys in map while ranging over it with Go 1. map, concurrent-map, sync. "It works under load testing" — with 10 users. When multiple goroutines read and write to a map without proper synchronization, a race condition occurs. For go, most things are not thread safe, including maps and slices, however channels are thread safe. Map when you need a concurrent-safe map and expect unpredictable read/write patterns. Contribute to orcaman/concurrent-map development by creating an account on GitHub. RWMutex封装map实现线程安全，提供readMap和writeMap方法控制并发访问。替代方案还包括channel和sync. The synchronized map and the channel-based map are two different approaches to concurrent map iteration. Jul 10, 2024 · What did you do? sorry i can't upload the complete code, my code invoke (sync. Jan 23, 2026 · Go maps are not safe for concurrent access. Mar 12, 2025 · Use sync. Jul 16, 2021 · Learn how to effectively handle concurrent map operations in Go using sync. Go is expressive, concise, clean, and efficient. 这也是 The first is the most common method of using mutex locks or read-write locks; The second is to compare the Golang-specific methods, start a single coroutine to read and write the map, and when other coroutines need to read and write the map, send signals to the coroutine through the channel. Jun 15, 2020 · concurrent read/write Map fatal error: concurrent map iteration and map write 使用Sync Map 後 Use Sync Map 改成這樣就沒問題拉，下次再分享一下 Go 中的 Lock 用法 參考資料 The provided content discusses concurrency issues with Go's maps and how to safely use them with synchronization mechanisms, including the built-in data race detector and sync. RWMutex或第三方包如concurrent-map、sync. By understanding and applying these safe practices, you ensure your programs are robust and panic-free when accessing maps concurrently. Although the standard library sync. Jun 18, 2019 · Also depending how frequently new height managers are created and added to the map, it may be profitable to use a sync. Bidirectional communication means that one goroutine will send a message and the other will read it. If you need to read from Sep 24, 2021 · By reading this article, we have clarified the sync. Map). RWMutex. In Go 1. Learn best practices, avoid common pitfalls, and write efficient concurrent code in Go. As always, if one goroutine is writing to a map, no other goroutine should be reading or writing the map concurrently. The sync. Nov 26, 2024 · Go provides several synchronization mechanisms to address these challenges, allowing developers to safely and efficiently execute concurrent operations. 9之前，go语言标准库中并没有实现并发 map。 在Go 1. if multiple goroutines read and write to a map concurrently without synchronization: we risk a fatal error: concurrent map writes. Its concurrency mechanisms make it easy to write programs that get the most out of multicore and networked machines, while its novel type system enables flexible and modular program construction. But this slows down your program. Golang, concurrent programming, sync. Map and mutex solutions to avoid data race conditions and improve application performance. Feb 6, 2026 · The overall purpose of this code is to demonstrate the concurrent usage of a sync. Map, along with performance considerations for choosing between a standard map with a lock and a sync. In this article, we will explore how to use the `sync. Built-in map& sync. marshal to string,或者其他方式对map 执行了read、write操作。 而业务逻辑同步写对象map值，那么，就会触发: fatal error: concurrent map read and map write 本质原因在于：两个goroute对同一个map执行了读写并发，而golang map默认是不 The sync. There's also the concurrency-safe `sync. Map supports concurrent read and write maps, it is more suitable for scenarios with more reads and less writes, because the performance of its writing is relatively poor, so you must consider this when using it. You'll have to learn how to synchronise access. " Your situation is not specific. Map allows you to safely work with maps in concurrent Go applications. Jan 18, 2018 · I have met multiple people new-ish to Go that guarded map reads with locks, or used third-party concurrent maps for just concurrent reads. This article dives into how sync. 7 concurrency bugs that pass code review every time: 1. As far as I know, map is not safe for concurrent read/write… Dec 27, 2022 · Go语言中未同步控制的map在高并发读写时会引发fatal错误，可通过sync. If one goroutine is writing to a … Jun 23, 2023 · "How to solve golang fatal error: concurrent map write" don't write concurently to a map. The extensions are stored in a map[string]struct{} that I pass to each goroutine, and for each file, I check to see if the file extension is in the map. If one goroutine is writing Go was designed at Google in 2007 to improve programming productivity in an era of multicore, networked machines and large codebases. Feb 2, 2023 · In this article, we’ll dive into the reasons behind the restriction on concurrent read and write from maps and provide practical solutions to prevent these issues in your Go code Nov 24, 2024 · Using sync. Let's say, your map is written first and never be written again then you don't need any mutex type of thing to make sure that only one go routine is accessing your map. Aug 20, 2023 · I have a map of maps: map[string]map[string]*Struct which I need to read/write in multiple Go routines. 9. 2016 I don't want to read lock the map That makes sense, since a deleting from a map is considered a write operation, and must be serialized with all other reads and writes. Map或channel实现安全并发访问，避免资源竞争问题。 How and when to use Go maps. Sep 22, 2019 · Could you please show how it’s implemented in the main function? Like a writing and reading example Yamil_Bracho (Yamil Bracho) September 22, 2019, 5:23pm 4 Jan 7, 2022 · The concurrent read/write map we talked about earlier is actually a fatal error as well. Build simple, secure, scalable systems with Go An open-source programming language supported by Google Easy to learn and great for teams Built-in concurrency and a robust standard library Large ecosystem of partners, communities, and tools Mar 4, 2026 · golang-concurrency // Go concurrency patterns, context propagation, goroutine lifecycle, channel ownership, sync primitives, goroutine leak prevention, and race detector usage. Nov 27, 2024 · In Go, concurrency is a powerful feature that allows functions to run independently and interact through shared data. Use map + RWMutex for read-heavy workloads, as it allows multiple readers to access data simultaneously. Time might be spent in deciding who among the workers gets the next item. You can read more about it in the golang repo, for example here and here Here we fork some README document from concurrent-map Feb 27, 2025 · Go’s built-in map type does not provide synchronization. What is the best way to achieve this ? a Mutex or RWMutex ? and where to place it ? if I use Feb 26, 2022 · Golang data race cause by concurrent map read Asked 4 years ago Modified 1 year, 10 months ago Viewed 2k times fatal error: concurrent map read and map write #3271 Open nickdooley2016 opened this issue on Aug 7, 2022 · 2 comments. If that is the case with you then you need to be careful because go maps are not safe for concurrent use. (source: this answer) Assuming the worst case scenario (multiple writers and readers), you can take a look at the implementation of orcaman/concurrent Sep 24, 2021 · 在之前的 《为什么 Go map 和 slice 是非线程安全的？》 文章中，我们讨论了 Go 语言的 map 和 slice 非线程安全的问题，基于此引申出了 map 的两种目前在业 Jan 20, 2023 · Safe map data structure Creating a concurrent safe map in Go is relatively easy, as the language provides built-in support for concurrency and synchronization. Apr 11, 2021 · Solution: golang have RWMutex in sync package to solve this Problem, it also prevents reccursive reads RWMutex is reader/writer mutual exclusion lock,The lock can be hold by arbitary number of Sep 22, 2025 · Golang - Data Structures - Concurrency with Maps Introduction A critical point to understand about Go’s built-in map type is that it is not safe for concurrent use. 2 #6216 (Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion. Map` type to store and retrieve data concurrently in Go. Map was introduced. Jun 10, 2025 · Enter sync. The optimal solution depends on the specific use case and its requirements. So if you want to use the map for something more like in-memory db, you might benefit from using our version. We would like to show you a description here but the site won’t allow us. RWMutex, sync. The synchronized map uses locks to protect the map from concurrent access, while the channel-based map uses channels to coordinate access to the map. Map, and other concurrency patterns to avoid race conditions. sync. It has special features like lock-free reads and fine-grained locking mechanisms, simplifying concurrent programming. The article dedicated to the maps in Nov 6, 2016 · The "Go maps in action" entry in the Go blog states: Maps are not safe for concurrent use: it's not defined what happens when you read and write to them simultaneously. Dec 4, 2015 · Original answer Nov. Dec 21, 2022 · In concurrent programming, Go provides channels that you can use for bidirectional communication between goroutines. This definitely warrants a hint or a tip somewhere for beginners. You can read more about it in the golang repo, for example here and here usage Import the package: import ( Jun 16, 2012 · When you use a map in a program with concurrent access, is there any need to use a mutex in functions to read values? 231K subscribers in the golang community. So your scenario is not safe and can result in a panic as well as other undefined behavior. 8k Star 133k Dec 23, 2016 · Go detects concurrent read and write on map despite locks Asked 8 years, 2 months ago Modified 8 years, 2 months ago Viewed 718 times Feb 21, 2023 · Comparing Go performance of Mutex, sync. Map data structure. For instance two of the most commonly used types in Go - slice and map - cannot be used safely from multiple goroutines without the risk of having a race condition. Multiple goroutines perform both write and read operations concurrently, showcasing how synchronization is handled by the sync. Map type stores keys and values of any type (using the empty interface). Loads, stores, and deletes run in amortized constant time. Map works under the hood, from its two-map system to the bottom line of expunged entries. Dec 5, 2021 · 源码解析高性能并发安全map concurrent-map，采用32个分片降低锁粒度提升性能，提供丰富接口及回调功能，基准测试显示其性能优于sync. But this could be more of a workaround according to your use case. Community default. Production has 10,000. Oct 31, 2024 · The above outlines various solutions for concurrent map access in Golang, and many other methods exist as well. rktbum vzn jeqz bvi mxkku mruk qjw qvh ufbej zgrb