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<div class="moz-cite-prefix">Thanks for the feedback guys.<br>
<br>
Studying the code, I had figured going with a straight int would
in practice be most efficient and not run into multi-threaded
problems, even if initially appearing a bit risky. I will rework
it to use a std::condition_variable. That will be more robust and
readable.<br>
<br>
Shawn.<br>
<br>
On 7/29/2014 10:53 AM, Zachary Turner wrote:<br>
</div>
<blockquote
cite="mid:CAAErz9jD07cDjWmmOofQKJXHKHjECyN3Q7T=N2j9=ndx8ZsVPA@mail.gmail.com"
type="cite">
<div dir="ltr">Even better would be an std::condition_variable</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Mon, Jul 28, 2014 at 10:30 PM,
Matthew Gardiner <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:mg11@csr.com"
target="_blank">mg11@csr.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Shawn,<br>
<br>
I use 64-bit linux and I see this issue a lot. It usually
manifests itself as the prompt just not being printed (or
perhaps it just gets overwritten) - regardless - I invoke a
command, and I don't see an (lldb) prompt when I should. So
I'm well pleased that you are looking at this!<br>
<br>
Would it not be more robust to use a semaphore than usleep
to synchronise the problematic threads?<br>
<br>
Although I've not looked too deeply into this particular
issue, whenever I've seen similar races, I found that it's
almost impossible to pick the right value when using a sleep
command. A semaphore, though, should always ensure the
waiting thread will wake precisely.<br>
<br>
I'd be happy to help to test such a fix.<br>
<br>
Matt<br>
<br>
<br>
Shawn Best wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div class="h5">
Hi,<br>
<br>
I have attached a patch which addresses 3 related race
conditions that cause the command line (lldb) prompt
to get displayed inappropriately and make it appear it
is not working correctly. This issue can be seen on
linux and FreeBSD. I can also artificailly induce the
problem on OSX.<br>
<br>
The issue happens when the command handler (in the
main thread) issues a command such as run, step or
continue. After the command finishes initiating its
action, it returns up the call stack and goes back
into the main command loop waiting for user input.
Simultaneously, as the inferior process starts up,
the MonitorChildProcess thread picks up the change and
posts to the PrivateEvent thread. HandePrivateEvent()
then calls PushProcessIOHandler() which will disable
the command IO handler and give the inferior control
of the TTY. To observe this on OSX, put a<br>
<br>
usleep(100);<br>
<br>
immediately prior the PushProcessIOHandler() in
HandlePrivateEvent.<br>
<br>
<br>
My proposed solution is that after a 'run', 'step', or
'continue' command, insert a synchronization point and
wait until HandlePrivateEvent knows the inferior
process is running and has pushed the IO handler. One
context switch (<100us) is usually all the time it
takes on my machine. As an additional safety, I have
a timeout (currently 1ms) so it will never hang the
main thread.<br>
<br>
Any thoughts, or suggestions would be appreciated.<br>
<br>
Regards,<br>
Shawn.<br>
<br>
<br>
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