On Feb 2, 2006, at 10:27 AM, Guilhem Lavaux wrote:
Casey Marshall wrote:
On Jan 31, 2006, at 6:10 PM, David P Grove wrote:
Jikes RVM also does m-to-n threading, so it's there's more than 1 VM
that's whacky in this regard. The things we need to do are most
likely
different than what Kaffe needs to do, but having a chance to
inject a VM
callback before the thread dives off into a blocking system call is
something we would like to be able to do. We have some linux
specific
hacks (evil with dlopen to intercept poll, select, etc), but
it's fragile
and doesn't work on other platforms like AIX and OS X that Jikes
RVM runs
on.
Would my suggestion for Enter/Exit callbacks help this?
Though enter/exit callbacks may help for a few syscalls but it
won't for some (like blocking read/write). For these new calls you
need handle blocking queues in the VM thread scheduler. That needs
to put the fd into non-blocking mode and when you do a read you
first check if there is any data (in non-blocking mode) and if
there is not data then the thread system queues the current thread
and tells the scheduler to jump somewhere else until some datas are
available on the specified fd. So we must really stick to rerouting
a few IOs. I am sure that handling m-to-n threading system is as
difficult as what we are doing (maybe more).
Aha, I grok the issue now. Would it make sense to do conditional
compilation based on a "green threads" model, so that you can compile
all blocking I/O calls to support such a model, if configured thusly?
Or would file descriptor callbacks help -- where the FD is put into
non-blocking mode before the call, then reset after, with support to
catch the `EAGAIN' if it arrives?
Also, I'm sure you could write a kernel-threads compatible library
that also supported user-mode thread models at the same time (the
restrictions on the former seem to be a subset of the latter), but
don't know about what performance drain that would incur on kernel
threaded systems. Because, "one POSIX library to rule them all," that
supported both thread models, would still be an awesome thing.
