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).

2 files changed, 24 insertions, 0 deletions

diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index 68344f9..9424bf1 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -375,6 +375,16 @@ is a separate error indicator for each thread.
    .. % thread.interrupt_main() (used from IDLE), so it's still needed.
 
 
+.. cfunction:: int PySignal_SetWakeupFd(int fd)
+
+   This utility function specifies a file descriptor to which a ``'\0'`` byte will
+   be written whenever a signal is received.  It returns the previous such file
+   descriptor.  The value ``-1`` disables the feature; this is the initial state.
+   This is equivalent to :func:`signal.set_wakeup_fd` in Python, but without any
+   error checking.  *fd* should be a valid file descriptor.  The function should
+   only be called from the main thread.
+
+
 .. cfunction:: PyObject* PyErr_NewException(char *name, PyObject *base, PyObject *dict)
 
    This utility function creates and returns a new exception object. The *name*
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 @@ The :mod:`signal` module defines the following functions:
    :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