select: Add initial epoll implementation.

epoll is chosen as most efficient on Linux and FFI-friendly.

select/select.py

@@ -0,0 +1,51 @@
+import ffi
+import struct
+import os
+
+
+libc = ffi.open("libc.so.6")
+
+#int epoll_create(int size);
+epoll_create = libc.func("i", "epoll_create", "i")
+#int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
+epoll_ctl = libc.func("i", "epoll_ctl", "iiip")
+#int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout);
+epoll_wait = libc.func("i", "epoll_wait", "ipii")
+
+EPOLLIN = 0x001
+EPOLLPRI = 0x002
+EPOLLOUT = 0x004
+
+EPOLL_CTL_ADD = 1
+EPOLL_CTL_DEL = 2
+EPOLL_CTL_MOD = 3
+
+
+class Epoll:
+
+    def __init__(self, epfd):
+        self.epfd = epfd
+        self.evbuf = struct.pack("IQ", 0, 0)
+
+    def register(self, fd, eventmask=EPOLLIN|EPOLLPRI|EPOLLOUT, retval=None):
+        if retval is None:
+            retval = fd
+        s = struct.pack("IQ", eventmask, retval)
+        r = epoll_ctl(self.epfd, EPOLL_CTL_ADD, fd, s)
+        os.check_error(r)
+
+    def poll(self, timeout=-1):
+        s = bytearray(self.evbuf)
+        n = epoll_wait(self.epfd, s, 1, timeout)
+        os.check_error(n)
+        res = []
+        if n > 0:
+            ev, h = struct.unpack("IQ", s)
+            res.append((h, ev))
+        return res
+
+
+def epoll():
+    fd = epoll_create(4)
+    os.check_error(fd)
+    return Epoll(fd)