Fixed debugger_test to wait until target process is dead

Fixed debugger_test to wait until target process is dead

R=hausner@google.com

Committed: https://code.google.com/p/dart/source/detail?r=22775

[hausner, 2013-05-15 15:43:36]

LGTM but see my comment/question. I don't understand how the library works. Can
you please add a comment in the code?

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
File tests/standalone/debugger/debug_lib.dart (right):

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
tests/standalone/debugger/debug_lib.dart:505: print("Could not send kill signal
to target process.");
After printing this, you still wait for the target process to exit? Could this
not lead to hangs if the target process hangs?

[ricow1, 2013-05-16 07:19:55]

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
File tests/standalone/debugger/debug_lib.dart (right):

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
tests/standalone/debugger/debug_lib.dart:505: print("Could not send kill signal
to target process.");
On 2013/05/15 15:43:36, hausner wrote:
> After printing this, you still wait for the target process to exit? Could this
> not lead to hangs if the target process hangs?
From the api docs:
Returns true if the process is successfully killed (the signal is successfully
sent). Returns false if the process could not be killed (the signal could not be
sent). Usually, a false return value from kill means that the process is already
dead.

We use this extensively in infrastructure code and I have not seen any cases
where this happens and the process is not already dead. The future below will
then return immediately.

Additionally, there is not really any difference between having just the child
hang and to have this hang as well. This process will be killed by the testing
script if it hangs.

[kustermann, 2013-05-16 08:06:08]

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
File tests/standalone/debugger/debug_lib.dart (right):

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
tests/standalone/debugger/debug_lib.dart:505: print("Could not send kill signal
to target process.");
On 2013/05/15 15:43:36, hausner wrote:
> After printing this, you still wait for the target process to exit? Could this
> not lead to hangs if the target process hangs?
We wait for the exitCode and if the target process is already dead, we will get
the exitCode immediately.

Maybe this example helps you understand why this works:
main() {
  var c = new Completer();
  c.complete(true);

  Timer.run(() {
    c.future.then((_) => print("done"));
  }); 
}
In this example we make a completer and complete it immediately (this is the
same as the process already exited). We schedule then a new callback (which is
inserted into the event loop). This callback registers on the future and gets
executed immediately (because the completer was already completed).

[kustermann, 2013-05-16 08:08:01]

Committed patchset #2 manually as r22775 (presubmit successful).

[hausner, 2013-05-16 15:38:32]

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
File tests/standalone/debugger/debug_lib.dart (right):

https://codereview.chromium.org/14773038/diff/1/tests/standalone/debugger/deb...
tests/standalone/debugger/debug_lib.dart:505: print("Could not send kill signal
to target process.");
Thanks for the explanation Rico and Martin. Thinking about this some more, it
might make sense to simplify close() and always make sure the target process
exits. I will make that change later.