On Dec 8, 2007 2:56 PM, <[EMAIL PROTECTED]> wrote: > On 05:20 pm, [EMAIL PROTECTED] wrote: > >The best solution I can think of is to add a new API that takes a > >signal and a file descriptor and registers a C-level handler for that > >signal which writes a byte to the file descriptor. You can then create > >a pipe, connect the signal handler to the write end, and add the read > >end to your list of file descriptors passed to select() or poll(). The > >handler must be written in C in order to avoid the race condition > >referred to by Glyph (signals arriving after the signal check in the > >VM main loop but before the select()/poll() system call is entered > >will not be noticed until the select()/poll() call completes). > > This paragraph jogged my memory. I remember this exact solution being > discussed now, a year ago when I was last talking about these issues. > > There's another benefit to implementing a write-a-byte C signal handler. > Without this feature, it wouldn't make sense to have passed the > SA_RESTART flag to sigaction, because and GUIs written in Python could > have spent an indefinite amount of time waiting to deliver their signal > to Python code. So, if you had to handle SIGCHLD in Python, for > example, calls like file().write() would suddenly start raising a new > exception (EINTR). With it, you could avoid a whole class of subtle > error-handling code in Twisted programs.
SA_RESTART still isn't useful. The low-level poll call (not write!) must stop and call back into python. If that doesn't indicate an error you can safely restart your poll call though, and follow it with a (probably non-blocking) write. Note that the only reason to use C for a low-level handler here is give access to sigatomic_t and avoid needing locks. If you ran the signal handler in a background thread (using sigwait to trigger them) you could use a python handler. -- Adam Olsen, aka Rhamphoryncus _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
