从goroutine写入STDOUT时避免混乱的输出

Question

When writing to stdout or a log, how can I make sure that the output from several goroutines aren't messing up the output?

e.g. make sure the output will be like this

Routine 1 found 1235 entries
Routine 3 found 999 entries
Routine 2 found 24 entries

and NOT like this

Routine 1 fouRoutine 3 found 999 entries
nd 1235 entriRoutine 2 found 24 entries
es

I mean the output from one goroutine is not writing at the same time as another

i.e. is there a library or a standard way to get a semaphore around the output?

Answer 1

Use the log package for logging. From log.Logger:

A Logger represents an active logging object that generates lines of output to an io.Writer. Each logging operation makes a single call to the Writer's Write method. A Logger can be used simultaneously from multiple goroutines; it guarantees to serialize access to the Writer.

The fmt package is generally not safe to use with more than one goroutine.

If time (synchronizing of lock) is of concern, prepend the log statement with go:

go log.Println("some log")

Note however, that the log output then may be (most certainly) delayed.