Patch #1583 by Adam Olsen.
This adds signal.set_wakeup_fd(fd) which sets a file descriptor to
which a zero byte will be written whenever a C exception handler runs.
I added a simple C API as well, PySignal_SetWakeupFd(fd).
diff --git a/Doc/library/signal.rst b/Doc/library/signal.rst
index 54cce53..afb3166 100644
--- a/Doc/library/signal.rst
+++ b/Doc/library/signal.rst
@@ -110,6 +110,20 @@
:manpage:`signal(2)`.)
+.. function:: set_wakeup_fd(fd)
+
+ Set the wakeup fd to *fd*. When a signal is received, a ``'\0'`` byte is
+ written to the fd. This can be used by a library to wakeup a poll or select
+ call, allowing the signal to be fully processed.
+
+ The old wakeup fd is returned. *fd* must be non-blocking. It is up to the
+ library to remove any bytes before calling poll or select again.
+
+ When threads are enabled, this function can only be called from the main thread;
+ attempting to call it from other threads will cause a :exc:`ValueError`
+ exception to be raised.
+
+
.. function:: signal(signalnum, handler)
Set the handler for signal *signalnum* to the function *handler*. *handler* can