[cdt-dev] An FYI on starter.cxx

[Chris Songer <songer@xxxxxxxxxxxxx>]

Hi!

I found a case where on Windows2000 calling Spawner::destroy() would end
up hanging the thread calling it. The case was a little confusing but
basically a launcher was spawning a windows app that caught CTRL_C_EVENT
and ignored. That meant that the TerminateProcess call was the thing
actually killing the process. Quoting from the windows docs on
TerminateProcess:

Use it only in extreme circumstances. The state of global data maintained
by dynamic-link libraries (DLLs) may be compromised if
TerminateProcess is used rather than
ExitProcess.

The lockup happened when Spawner.destroy() went to close stderr.
iostreams::SpawnerInputStream_close0 hung under CloseHandle(). The
handles were all correct, nothing had been corrupted, I can only assume
that what the quote above warned about actually happened.

To fix my case, I added a GenerateConsoleCtrlEvent(CTRL_BREAK_EVENT, 0 )
to the existing CTRL_C_EVENT in starter.exe to send a signal that the app
was not catching and ignoring. The lockup went away. Clearly this would
not be a fix if the spawned application were also catching
CTRL_BREAK_EVENT, so it's not a generic solution. 

Probably the "right" fix is a two stage shutdown where you try
a signal first, if that works you know you can close the file descriptors
safely. If it does not, you expressly ask for TerminateProcess and shut
the filedescriptors with an awareness that the call to
Spawner*Stream.close() may hang. A return from Spawner.raise(x,TERM)
indicating if TerminateProcess had to be used would also work.

I'm not advocating all that work -- it's surely not worth it unless
someone actually comes up with the case. Just an FYI.

Thanks,
-Chris