sio: advisory locks

1 files changed, 57 insertions, 0 deletions

diff --git a/luxio/simple.lua b/luxio/simple.lua
index 81c5b11..8040e6b 100644
--- a/luxio/simple.lua
+++ b/luxio/simple.lua
@@ -70,6 +70,19 @@
 -- myfile:nogc()
 --         do not close the descriptor on garbage collect
 --
+-- myfile:lock(mode, whence, start, len, wait)
+--         Manipulates advisory locks on file regions.
+--         mode is one of "r", "w", or "", for read lock, write lock, or
+--         unset lock.  whence, like seek, one of "cur", "set", "end".
+--         start and len describe the region.  If wait is set, it will
+--         wait until the lock is available before claiming it and
+--         returning.
+--
+-- myfile:locktest(mode, whence, start, len)
+--         As above, but it does not claim the lock, just checks if it
+--         is available.  Returns true if the lock would work, or false
+--         and a pid of the holder if the lock is already taken.
+--
 -- myfile = sio.wrap_fd(fd[, nogc][, name])
 --         wrap an fd aquired elsewhere with functions here
 --         fd: number of file descriptor
@@ -588,6 +601,48 @@ local function seek(o, whence, offset)
    return r
 end
 
+local function lock(o, rw, whence, offset, len, wait, test)
+   sio_check_mt(o)
+   assert(rw == "r" or rw == "w" or rw == "")
+   assert(seek_modes[whence])
+   assert(type(offset) == "number")
+   assert(type(len) == "number" and len >= 0)
+
+   local flock = {
+      l_whence = seek_modes[whence],
+      l_start = offset,
+      l_len = len
+   }
+
+   local cmd = wait and l.F_SETLKW or l.F_SETLK
+   if test then cmd = l.F_GETLK end
+
+   if rw == "r" then flock.l_type = l.F_RDLCK
+   elseif rw == "w" then flock.l_type = l.F_WRLCK
+   else flock.l_type = l.F_UNLCK
+   end
+
+   local r, errno = l_fcntl(o.fd, cmd, flock)
+
+   if r < 0 then
+      return err("fcntl", errno)
+   end
+
+   if not test then
+      return true
+   else
+      if flock.l_type == l.F_UNLCK then
+	 return true
+      else
+	 return false, flock.l_pid
+      end
+   end
+end
+
+local function locktest(o, type, whence, offset, len)
+   return lock(o, type, whence, offset, len, false, true)
+end
+
 local function chmod(file, mode)
    local mode = sio_mode_flags(mode)
    local r, errno = l_chmod(file, mode)
@@ -916,6 +971,8 @@ descriptor_mt = {
    fchmod = fchmod,
    stat = fstat,
    fstat = stat,
+   lock = lock,
+   locktest = locktest,
 
    accept = accept,
    setsockopt = msetsockopt,