将多个goroutine打印到stdout是否安全？
I have multiple goroutines in my program, each of which makes calls to fmt.Println without any explicit synchronization. Is this safe (i.e., will each line appear separately without data corruption), or do I need to create another goroutine with synchronization specifically to handle printing?
我的程序中有多个goroutine，每个goroutine都调用 fmt.Println code> 没有任何明确的同步。 这样安全吗（也就是说，每行会单独出现而不会破坏数据），还是我需要创建另一个具有同步功能的goroutine来专门处理打印？ p>
div>
No it's not safe even though you may not sometimes observe any troubles. IIRC, the fmt package tries to be on the safe side, so probably intermixing of some sort may occur but no process crash, hopefully.
This is an instance of a more universal Go documentation rule: Things are not safe for concurrent access unless specified otherwise or where obvious from context.
One can have a safe version of a nice subset of fmt.Print* functionality using the log package with some small initial setup.
Everything fmt does falls back to w.Write() as can be seen here. Because there's no locking around it, everything falls back to the implementation of Write(). As there is still no locking (for Stdout at least), there is no guarantee your output will not be mixed.
I'd recommend using a global log routine.
Furthermore, if you simply want to log data, use the log package, which locks access to the output properly.
See the implementation for reference.
The common methods (fmt.printLine) are not safe. However, there are methods that are.
log.Logger is "goroutine safe": https://golang.org/pkg/log/#Logger
Something like this will create a stdout logger that can be used from any go routine safely.
logger := log.New(os.Stdout, "", 0)