Can Concurrent Reads and Writes to Go Structs Work Without Locks, and Why Is It Risky?

Golang Struct Concurrent Read and Write Without Lock: Why Possible but Risky

It has been observed that concurrent read and write operations on a struct in Go can operate without a lock and still function without apparent issues. This is exemplified by the concurrentStruct() function provided, which involves two goroutines continuously altering a shared struct's field. Despite warnings indicating potential data races, the code executes successfully.

This behavior arises from Go's memory model and the fact that structs are passed by reference, meaning that all goroutines are working on the same instance of the struct. As long as the individual field accesses are atomic, there is no guarantee of data corruption.

However, such behavior is highly discouraged and can lead to unpredictable outcomes. Unsynchronized concurrent access to any variable from multiple goroutines, where at least one is a write, is considered undefined behavior in Go. It could result in incorrect results, crashes, or other unexpected consequences.

Contrast with Protected Access

In contrast, the concurrentStructWithMuLock() function uses a read-write mutex to synchronize access to the struct. This eliminates the possibility of data races and ensures consistent behavior, as evidenced by the absence of race condition warnings.

Map Concurrency Issues

The concurrentMap() function highlights a different issue related to concurrency. Go 1.6 introduced lightweight detection of concurrent misuse of maps. If multiple goroutines attempt to concurrently read or write to the same map without proper synchronization, the runtime intentionally crashes the program to prevent undefined behavior. This behavior is triggered by the race detector and underscores the importance of using synchronization mechanisms for concurrent map operations.

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