Is Concurrent Printing to Stdout in Go Safe?

Multiple Goroutines Printing to Stdout: Safety Concerns

In Go concurrency, it's tempting to have multiple goroutines print messages directly to stdout using fmt.Println without implementing any synchronization. However, this approach raises the question: "Is it safe?"

Unsafe Intermixing

The answer is a resolute no. Printing to stdout is not inherently thread-safe in Go. Without proper synchronization, it's possible for data from different goroutines to get intermixed, resulting in corrupted output.

According to the fmt package documentation, the package does attempt to provide safe printing to stdout. However, this safety is not guaranteed, and data may still be corrupted in certain circumstances.

Concurrent Access Rule

This issue highlights a fundamental rule in Go: things are only safe for concurrent access when explicitly stated or when it's obvious from the context. In the case of printing to stdout, neither of these conditions applies.

Safe Printing Alternative

To ensure safe printing in concurrent programs, it's recommended to use the log package instead of fmt. The log package provides a buffered logging mechanism that serializes and writes messages in a thread-safe manner. By setting up a global logger and utilizing its thread-safe methods, you can achieve safe logging in your concurrent programs.

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