flesh out kqueue library

Have not tried to build this yet. But barring minor mistakes, I think it's
good.

Utility/Kqueue.hs

@@ -25,6 +25,8 @@ import qualified Data.Map as M
 
 type DirMap = M.Map Fd FilePath
 
+data Kqueue = Kqueue Fd DirMap
+
 {- Builds a map of directories in a tree, possibly pruning some.
  - Opens each directory in the tree. -}
 scanRecursive :: FilePath -> (FilePath -> Bool) -> IO DirMap
@@ -43,25 +45,33 @@ addSubDir dirmap dir prune = M.union dirmap <$> scanRecursive dir prune
 removeSubDir :: FilePath -> DirMap -> DirMap
 removeSubDir dir = M.filter (not . dirContains dir)
 
-foreign import ccall unsafe "libkqueue.h waitchange" c_waitchange
-	:: Ptr Fd -> IO Fd
+foreign import ccall unsafe "libkqueue.h init_kqueue" c_init_kqueue
+	:: CInt -> Ptr Fd -> IO Fd
+foreign import ccall unsafe "libkqueue.h waitchange_kqueue" c_waitchange_kqueue
+	:: Fd -> IO Fd
 
-{- Waits for a change in a map of directories, and returns the directory
- - where the change took place. 
+{- Initializes a Kqueue to watch a map of directories. -}
+initKqueue :: DirMap -> IO Kqueue
+initKqueue dirmap = withArrayLen (M.keys dirmap) $ \fdcnt c_fds ->
+	h <- c_init_kqueue (fromIntegral fdcnt) c_fds
+	return $ Kqueue h dirmap
+
+{- Stops a Kqueue. Note: Does not directly close the Fds in the dirmap,
+ - so it can be reused.  -}
+stopKqueue :: Kqueue -> IO
+stopKqueue (Kqueue h _) = closeFd h
+
+{- Waits for a change on a Kqueue, and returns the directory
+ - or directories where a change took place.
  -
  - The kqueue interface does not tell what type of change took place in
  - the directory; it could be an added file, a deleted file, a renamed
  - file, a new subdirectory, or a deleted subdirectory, or a moved
  - subdirectory.
  -
- - Note that if subdirectories have changed, the caller will want to
- - update the map before calling this again. -}
-waitChange :: DirMap -> IO (Maybe FilePath)
-waitChange dirmap = withArray (M.keys dirmap) $ \c_fds -> do
-	changed <- c_waitchange c_fds
-	ifM (safeErrno <$> getErrno)
-		( return $ M.lookup changed dirmap
-		, return Nothing
-		)
-	where
-		safeErrno (Errno v) = v == 0
+ - Note that if subdirectories have changed, the caller should re-run
+ - initKqueue to get them watched. -}
+waitChange :: Kqueue -> IO [FilePath]
+waitChange (Kqueue h dirmap) = do
+	changed <- c_waitchange_kqueue h
+	return $ M.lookup changed dirmap

Utility/libkqueue.c

@@ -5,18 +5,62 @@
  * Licensed under the GNU GPL version 3 or higher.
  */
 
-#include <errno.h>
 #include <stdio.h>
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/event.h>
+#include <sys/time.h>
 
-/* Waits for a change event on one of the array of directory fds,
- * and returns the one that changed. */
-int waitchange(const int *fds) {
-//	if (kqueue(blah, &fds) != 0)
-//		return 0; /* errno is set */
-//	else
-		errno = 0;
+/* Initializes a kqueue, with a list of fds to watch for changes.
+ * Returns the kqueue's handle. */
+int init_kqueue(const int fdcnt, const int *fdlist) {
+	struct nodelay = {0, 0};
+	int kq;
 
-	printf("in waitchange!, %i %i\n", fds[0], fds[1]);
+	if ((kq = kqueue()) == -1) {
+		perror("kqueue");
+		exit(1);
+	}
 
-	return fds[0];
+	/* Prime the pump with the list of fds, but don't wait for any
+	 * change events. */
+	helper(kq, fdcnt, fdlist, &nodelay);
+
+	return kq;
+}
+
+/* Waits for a change event on a kqueue.
+ *
+ * Returns the fd that changed, or -1 on error.
+ */
+signed int waitchange_kqueue(const int kq) {
+	helper(kq, 0, NULL, NULL);
+}
+
+/* The specified fds are added to the set of fds being watched for changes.
+ * Fds passed to prior calls still take effect, so it's most efficient to
+ * not pass the same fds repeatedly.
+ */
+signed int helper(const int kq, const int fdcnt, const int *fdlist, cont struct *timeout) {
+	int i, nev;
+	struct kevent evlist[1];
+	struct kevent chlist[fdcnt];
+	
+	for (i = 0; i < fdcnt; i++) {
+		EV_SET(&chlist[i], fdlist[i], EVFILT_VNODE,
+			EV_ADD | EV_ENABLE | EV_CLEAR,
+			NOTE_WRITE,
+			1,
+			timeout);
+	}
+
+	nev = kevent(info->kq, info->chlist, info->cnt, info->evlist,
+			1, NULL);
+
+	if (nev == 1)
+		return evlist[0].ident;
+	else
+		return -1;
 }

Utility/libkqueue.h

@@ -1 +1,2 @@
-int waitchange(const int *fds);
+int init_kqueue(const int fdcnt, const int *fdlist);
+signed int waitchange_kqueue(const int kq);