[lldb-dev] gdb-remote lldb prompt race condition

[Greg Clayton]

The event should get delivered to the Debugger thread that is waiting for events and it should coordinate with the top io handler when printing it. If someone is grabbing the event manually by hijacking events, then we need to fix that code to send the event on to the unhijacked main event loop.


> On Aug 20, 2014, at 1:42 AM, Matthew Gardiner <mg11 at csr.com> wrote:
> 
> Hi folks
> 
> I have been seeing another issue with the display of the lldb prompt. This time it's when I do "target create elf-file", then "gdb-remote port-number". After the "gdb-remote" command I see the fact that my process is stopped, e.g.
> 
> Process 1 stopped
> 
> on the screen. But no (lldb) prompt.
> 
> Some investigation revealed that what's *probably* happening is the main thread after processing the "gdb-remote" returns to it's IOHandler, which then prints (lldb). However, the inferior's state changes seem to delivered to stdout via a different thread, basically one which sits in Debugger::DefaultEventHandler. This subsequent output then, I think, overwrites the previous (lldb) prompt.
> 
> Now in my (and presumably other people's) situation, this issue is compounded by the speed of the TCP/IP connection to the gdbserver stub, the "poll the hardware" nature of my stub, and the fact the hardware is actually simulated - yes over a TCP/IP socket.
> 
> FWIW, I resolved this by a horrible (POSIX only) hack, of sleeping for 300ms at the bottom of the CommandInterpreter::HandleCommand function.
> 
> @@ -9,6 +9,8 @@
> 
> #include "lldb/lldb-python.h"
> 
> +#include <poll.h> // MG for prompt bugs
> +
> #include <string>
> #include <vector>
> #include <stdlib.h>
> @@ -1916,6 +1918,9 @@
>     if (log)
>       log->Printf ("HandleCommand, command %s", (result.Succeeded() ? "succeeded" : "did not succeed"));
> 
> +    // MG wait for remote connects etc. to complete
> +    poll(0,0,300);
> +
>     return result.Succeeded();
> }
> 
> 
> But this is horrid. Given this, and other prompt issues, I'm wondering whether whether we need some brave soul, to redesign the current lldb IO handling mechanisms.
> 
> Matt
> 
> 
> 
> 
> 
> 
> 
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