Re: gdb-6.6 mingw port hangs after Ctrl-C

[Jim Blandy <jimb at codesourcery dot com>]

Christopher Faylor <cgf-use-the-mailinglist-please@sourceware.org>
writes:
> On Mon, Aug 20, 2007 at 03:31:28PM -0400, Daniel Jacobowitz wrote:
>>On Mon, Aug 20, 2007 at 10:16:12PM +0300, Eli Zaretskii wrote:
>>> The way to fix this is to make the signal handler stop the main thread
>>> as the first thing it does.  Then you have a Posix-compliant program
>>> again.  I did something similar for the MinGW port of GNU Make.
>>
>>Is there any way to force the other thread to longjmp?  Otherwise,
>>just stopping it isn't enough - you don't have the right stack.
>>Erm, maybe it would work anyway... longjmping from one thread to
>>another scares me a bit, though.
>
> This is why Cygwin's signal handling code is so complicated.
>
> You can stop another thread with a "SuspendThread()" call and you can
> cause the thread to resume in another location with a "ResumeThread()"
> by changing the EIP that is passed to it.  However, if you do that while
> you are in the middle of a low-level Windows function which, say, holds
> a mutex, then you are going to eventually run into problems.
>
> It's possible that this isn't a big problem for newer NT-based OSes but
> it was a show-stopper for the older versions of Windows and older
> versions of Windows NT.
>
> Cygwin works around this by not allowing itself to be suspended within a
> Cygwin1.dll function and checking for signal redirection at the end of
> any Cygwin function which references Windows.  If it notices that a
> signal came in then, instead of returning, the function will jump to the
> appropriate signal handler.  If the signal came in while user-level code
> was executing then the main thread is suspended and resumed at a new
> location which fixes up the stack so that the equivalent of a longjmp
> takes place.
>
> You *might* be able to make gdb do something similar to all of this but
> it would obviously be a lot of work.

GDB's quit_flag / immediate_quit / QUIT macro is set up for polling a
flag and handling interrupts at safe points.

The issue at hand here is that we need C-c to interrupt the main
thread as it reads from the remote host.  That could be a pipe, a
socket, or a serial port.

Do you know how one can safely interrupt each of these kinds of reads
in Windows?