I am trying to come up with a detailed definition of what a thread safe Go
program is (and is not). One that a (go) tool could check by analyzing the
code for me.
Here is what I got so far:
-
If there are no go statements, then the program is single threaded and
thus thread safe. I assume that we are only using go built in
concurrency primitives.
Otherwise:
-
A program is globals safe if any of this is true:
-
There are no global variables.
-
Globals are read only.
-
Globals are only ever modified by the same goroutine.
-
Globals are only accessed under the same mutex.
-
A program is thread-safe when it is globals safe AND any of these is
also true:
-
Goroutines only ever get variables, as arguments or from channels,
passed by copy.
-
After a reference is passed to another goroutine, the caller/sender
goroutine never access that reference again (it transferred “ownership”
of
it).
- Passed references are only accessed under the same mutex.
Of course, whether it is possible for a tool to check all this rules hold
or not is the real work.
But for now I just want to make sure I start with a complete and correct
definition of "thread safety in go".
Did I miss any possible source of races here?
Note that this kind of rule analysis is only possible for complete
programs, for which we know the whole set of code and can compute all
possible goroutine and mutex scopes.
Although my initial goal is for the tool to tell me definite answers
(thread safe or not), if that is not possible or too complex, I would also
think it's useful to have a tool that highlights risks (you might have not
noticed).
That way, you can decide to fix or let them be at development time, BEFORE
the dynamic race detector might flag real issues to you, probably already
in production!
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