apolyakov added inline comments.
================
Comment at: lit/tools/lldb-mi/target/inputs/target-select-so-path.py:8-11
+def get_free_port():
+ s = socket.socket()
+ s.bind(('', 0))
+ return s.getsockname()[1]
----------------
labath wrote:
> apolyakov wrote:
> > labath wrote:
> > > apolyakov wrote:
> > > > labath wrote:
> > > > > This is still racy, because the port can be snatched from under you
> > > > > between the time you get the free port and the time when lldb-server
> > > > > binds to it. If this was the only test doing it then it might be
> > > > > fine, but since this is going to be running concurrently with other
> > > > > tests, all of which are fetching free ports, the chances of that
> > > > > happening add up.
> > > > >
> > > > > (Also, binding to the wildcard address will trigger a firewall popup
> > > > > on some machines.)
> > > > There is a problem with getting port from lldb-server. If we run
> > > > `lldb-server gdbserver --pipe 0 ocalhost:0`, it'll print port number to
> > > > its stdout, but we can't get it using pipes since to do this we need to
> > > > wait until lldb-server finishes that isn't what we want.
> > > Aha, I see. lldb-server does not really expect you to pass std file
> > > descriptor as the --pipe argument. Normally you would create a separate
> > > fd and pass that instead. Doing that from python is a bit icky, but
> > > doable:
> > > ```
> > > (r, w) = os.pipe()
> > > kwargs = {}
> > > if sys.version_info >= (3,0):
> > > kwargs["pass_fds"] = [w]
> > > llgs = subprocess.Popen(["lldb-server", "gdbserver", "--pipe", str(w),
> > > ...], **kwargs)
> > > port_bytes = os.read(r, 10)
> > > port = int(port_bytes.decode("utf-8").strip('\x00'))
> > > ```
> > >
> > > Alternatively, we could modify lldb-server to print the port number to
> > > stdout in addition to any --pipe arguments (sounds like a good addition
> > > anyway, as it enables easy free port selection for a shell user), and
> > > then you can sniff that text from here.
> > `--pipe 0` prints port number exactly to stdout, so there will not be a
> > difference for us. It's not so simple to get port from lldb-server's stdout
> > in python, so I don't think it will save us.
> I think you're looking for this:
> ```
> foo = subprocess.Popen(...)
> print "The first line of output is: " + foo.stdout.readline()
> ```
>
> Btw, using `--pipe 0` works only by accident (0 is the stdin descriptor), and
> probably only in a terminal. Once popen() starts redirecting things, `0` will
> probably not refer to the thing that `stdout` will read from. `--pipe 1`
> would fix that, but then we have the issue that lldb-server will close the
> `--pipe` descriptor once it's finished writing the port. That can have
> surprising effects as subsequent attempts to write to stdout will fail.
> (That's why I suggested a different implementation. Among other things,
> outputting something like "lldb-server listening on 127.0.0.1:4747" will make
> it easier to separate out the port from other things that lldb-server happens
> to write to stdout.)
> I think you're looking for this:
>
> foo = subprocess.Popen(...)
> print "The first line of output is: " + foo.stdout.readline()
I tried this, it hangs for me.
https://reviews.llvm.org/D49739
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