Here's an updated webrev including Chris's proposal for early
prompt print outs for commands that could be interrupted
by event processing before command prompt delivery.
Issue: https://bugs.openjdk.java.net/browse/JDK-8169718
Webrev: http://cr.openjdk.java.net/~gadams/8169718/webrev.02/
Changes include
- removing the yield in vmInterrupted, to allow the event thread
output to be less interspersed
- improved the command prompts for cont, step, stepi and next
to be less likely to be interspersed with event output
- avoid NPE in printCurrentLocation if current thread is invalidated
On 8/6/18, 12:54 PM, Gary Adams wrote:
On 7/30/18, 12:46 PM, Chris Plummer wrote:
On 7/30/18 12:47 AM, serguei.spit...@oracle.com wrote:
Hi Chris,
Just one quick simple comment below.
On 7/29/18 22:05, Chris Plummer wrote:
Hi Gary,
I updated my changes to do the wait() for step, stepi, cont, and
next. Some issues turned up when testing. A number of tests were
timing out occasionally, I believe because sometimes the event was
handled (and the notify() call already completed) before we ever
got to the handler.wait() call.
I agree as I had this exact concern when was looking at the webrev.0.
Need more time to understand all the details.
Hopefully it's a moot point since my 2nd version doesn't rely on any
synchronization.
http://cr.openjdk.java.net/~cjplummer/8169718/webrev.01/
I think a properly working synchronized version would require a large
synchronized block in TTY::executeCommand() to block out any event
handling until the prompt has been printed. I think this is safe even
when you have a monitor command in place. Although that results in
TTY::executeCommand() being called from the event handler, and it may
temporarily block if the command thread is already in
TTY::executeCommand(), eventually the command thread will exit the
synchronized block allowing the event thread to make progress. Having
said that, I just assume stick with the simpler webrev above if no
one see issues with it.
I like the approach used here - to print the prompt immediately
and skip the the prompt at the bottom of the command processing.
The original error though was an interspersed prompt disrupting
the event handler output, which came from another event
being processed. e.g.
"Breakpoint hit:"
prompt from previous event
printCurrentLocation()
Let me try a few test runs with your patch
along with a diagnostic in printPrompt()
so we can identify the printPrompt caller.
new Exception().printStackTrace()
...
thanks,
Chris
Thanks,
Serguei
Although I never confirmed this was the cause, it certainly seems
feasible.
There were also issues with the prompt printed by
TTY:executeCommand(). I've come to realize that it should really
always be printed before any event handling. Currently that seems
to be the case, probably due to the Thread.yield() I mention below
in event handling code like stepEvent(), although I don't think
it's necessarily guaranteed. However, with my changes prompt was
always printed after the event was done being handled, and this
proved to be a problem for some tests.
When executing the "cont" command, it seems this prompt is expected
to be "> ", which is the prompt printed if the VM is not currently
suspended. Some tests count on this, mostly because they call
jdb.receiveReplyFor(), and pass in the number of prompts that are
expected. jdb.receiveReplyFor() does not count "> ". My change
ended up making the printPrompt() in TTY:executeCommand() print as
"main[1]" after a "cont" command, because the added synchronizing
was making it not print until the thread was suspended. This caused
some tests to fail because the expected reply was not yet received,
even after jdb.receiveReplyFor() had returned (it was basically
returning one prompt too soon).
I started thinking that the synchronized approach probably needs a
large synchronized block in TTY:executeCommand(). But then I
figured out a much easier solution. Thinking more about the
"prompt after cont" issue, it occurred to me that maybe we just
need to print out the prompt before executing the command, so it's
not possible for events to come in before the prompt is printed (or
worse yet, in the middle of event handling output). Doing this ends
up looking much like your original suggestion to set printPrompt =
false for "cont", "step", "stepi", and "next", except I also added
a call printPrompt() before doing this (Dan an I had rejected your
proposal to simply remove the prompt, since it did server a
purpose). For example:
} else if (cmd.equals("cont")) {
MessageOutput.printPrompt();
showPrompt = false;
evaluator.commandCont();
But this does cause the issue I brought up above that the prompt
from "cont" is expected (by a number of tests) to be "> ", but
since the above code is executed while the vm is suspended, it ends
up being main[1]. I fixed this by adding a "simple" argument to
printPrompt() so we can force it to be "> " when needed. This will
maintain compatibility with anyone making assumptions about what
the prompt should look like.
Here's the webrev, which seems to be working. I've run about 1000
iterations on all platforms. So far it seems to be working. There
have been some failures, but for the most part I've also seen those
with clean repos, and the ones that I haven't I don't believe are
related to my changes.
http://cr.openjdk.java.net/~cjplummer/8169718/webrev.01/
One other comment about your initial fix to set showPrompt = false:
+ showPrompt = false; // asynchronous command
I'm not sure if the "asynchronous command" comment was intentional
or just the result of the copy-and-paste. I just want to clarify
what is meant by "asynchronous command" in the other places where
this comment appears. There are a few commands that are executed
async on a different thread. If you look in Commands.java, you'll
see how these commands use the AsyncExecution class to handle
execution of the command. I'm not sure why this is done, because
all these commands look like ones that are inherently synchronous,
yet they are always run on a different thread, and as a result may
not be complete when execution returns to TTY::executeCommand().
These commands also all set showPrompt = false, but the prompt is
printed by AsyncExecution when complete. So, the point is the
commands which are inherently async, like "step" and "cont", are
not async w.r.t. these "asynchronous command" comments or the
AsyncExecution class.
Chris
On 7/27/18 4:27 PM, Chris Plummer wrote:
Hi Gary,
Sorry about the delay in the review. Been trying to fully
understand all the various code flows, which is tricky due to
having the separate event thread whose output needs to be
co-ordinated with command thread. Also made more complicated by
the multiple entrypoints into executeCommand(), and there being
various places where output produced and we care about the order.
I think I have it all mapped out now and a pretty good
understanding of how it all works.
My first impression is that it seems like a large number of
changes and a lot of passing around of a StringBuffer object to
fix a problem which I think could be resolved with some strategic
wait/notify code. For example, it might be as simple as doing
something like this:
http://cr.openjdk.java.net/~cjplummer/8169718/webrev.00/
This only covers the step command. You'd have to figure out which
other commands need to ensure an event has been processed before
printing the prompt, and set waitForEventCompletion = true for
them. Is there a reason not to go with something like this?
As for you current changes, just a couple of things I've noticed,
but I have not given it a thorough review (for example, making
sure that the StringBuffer is always eventually printed, and done
so in the right order).
In EventHandler.run(), it's unclear who is handling the printing
of sb when handleEvent() or handleDisconnectedException() are called.
In the following EventHandler code:
123 @Override
124 public void stepEvent(StepEvent se, StringBuilder sb) {
125 Thread.yield(); // fetch output
126 sb.append(MessageOutput.format("Step completed:"));
127 }
Do you understand why the Thread.yield() is there? What does the
comment mean by "fetch output"? Just seems like it has something
to do with the ordering of output, but it seems bad that the code
ever relied on a yield to make sure the output was ordered properly.
Also in the above code snippet, you need to be careful when
replacing MessageOutput.lnprint() with MessageOutput.format().
lnprint() adds a newline to the start of the line. That appears to
be missing in your code above.
thanks,
Chris
On 7/20/18 12:11 PM, Gary Adams wrote:
Here's another attempt to clear up the overlapping output from
the command processing and event handler in the jdb tests.
The fundamental problem is observed when "prompts"
are produced interleaved with command and event output.
This attempts to fix the issue by buffering the output and
printing it fully assembled.
Webrev: http://cr.openjdk.java.net/~gadams/8169718/webrev.01/
On 5/26/18, 6:50 AM, gary.ad...@oracle.com wrote:
This is a review request for a previously closed test bug.
The test was recently moved to the open repos, and the
proposed fix is in the open code.
Webrev: http://cr.openjdk.java.net/~gadams/8169718/webrev/
-------- Forwarded Message --------
Subject: RFR: JDK-8169718: nsk/jdb/locals/locals002: ERROR:
Cannot find boolVar with expected value: false
Date: Fri, 25 May 2018 11:35:10 -0400
From: Gary Adams <gary.ad...@oracle.com>
Reply-To: gary.ad...@oracle.com
The jdb tests use stdin to send commands to a jdb process
and parses the stdout to determine if a command was
successful and when the process is prompting for new commands
to be sent.
Some commands are synchronous, so when the command is completed
a new prompt is sent back immediately.
Some commands are asynchronous, so there could be a delay
until a breakpoint is reached. The event handler then sends a prompt
when the application thread is stopped and new jdb commands can be sent.
The problem causing the intermittent failures was a corruption in the
output stream when prompts were being sent at the wrong times.
Instead of receiving
"Breakpoint hit:"<location>
<prompt>
the log contained
"Breakpoint hit:"<prompt> <location>
Once out of sync, jdb commands were being sent prematurely
and the wrong values were being compared against expected behavior.
The simple fix proposed here recognizes that commands like "cont",
"step" and "next" are asynchronous commands and should not send back
a prompt immediately. Instead. the event handler will deliver the next prompt
when the next "Breakpoint hit:" or "Step completed:" state change occurs.
The bulk of the testing was done on windows-x64-debug builds where the
intermittent failures were observed in ~5 in 1000 testruns. The fix has
also been tested on linux-x64-debug, solaris-sparcv9-debug,
and macosx-x64-debug, even though the failures have never been reported
against those platforms.
Failures have been observed in many of the nsk/jdb tests with similar corrupted
output streams, but never directly associated with this issue before.
redefine001, caught_exception002, locals002, eval001, next001,
stop_at003, step002, print002, trace001, step_up001, read001,
clear004, kill001, set001
