diff --git a/builder.py b/builder.py
index 2085ec2..b22d873 100644
--- a/builder.py
+++ b/builder.py
@@ -1,6 +1,6 @@
-import sys, os, random, fcntl
+import sys, os, random
 import vars, jwack, state
-from helpers import log, log_, debug2, err, unlink
+from helpers import log, log_, debug2, err, unlink, close_on_exec
 
 
 def _possible_do_files(t):
@@ -31,14 +31,6 @@ def _nice(t):
     return os.path.normpath(os.path.join(vars.PWD, t))
 
 
-def _close_on_exec(fd, yes):
-    fl = fcntl.fcntl(fd, fcntl.F_GETFD)
-    fl &= ~fcntl.FD_CLOEXEC
-    if yes:
-        fl |= fcntl.FD_CLOEXEC
-    fcntl.fcntl(fd, fcntl.F_SETFD, fl)
-
-
 class BuildJob:
     def __init__(self, t, lock, shouldbuildfunc, donefunc):
         self.t = t
@@ -71,7 +63,7 @@ class BuildJob:
         state.stamp(dofile)
         unlink(tmpname)
         ffd = os.open(tmpname, os.O_CREAT|os.O_RDWR|os.O_EXCL)
-        _close_on_exec(ffd, True)
+        close_on_exec(ffd, True)
         self.f = os.fdopen(ffd, 'w+')
         # this will run in the dofile's directory, so use only basenames here
         argv = ['sh', '-e',
@@ -97,12 +89,18 @@ class BuildJob:
             os.chdir(dn)
         os.dup2(self.f.fileno(), 1)
         os.close(self.f.fileno())
-        _close_on_exec(1, False)
+        close_on_exec(1, False)
         os.execvp(self.argv[0], self.argv)
         assert(0)
         # returns only if there's an exception
 
     def _after(self, t, rv):
+        try:
+            self._after1(t, rv)
+        finally:
+            self._after2(rv)
+
+    def _after1(self, t, rv):
         f = self.f
         tmpname = self.tmpname
         if rv==0:
@@ -123,12 +121,13 @@ class BuildJob:
         else:
             if vars.VERBOSE or vars.XTRACE:
                 log('%s (done)\n\n' % _nice(t))
-        return self._after2(rv)
 
     def _after2(self, rv):
-        self.donefunc(self.t, rv)
-        assert(self.lock.owned)
-        self.lock.unlock()
+        try:
+            self.donefunc(self.t, rv)
+            assert(self.lock.owned)
+        finally:
+            self.lock.unlock()
 
 
 def main(targets, shouldbuildfunc):
diff --git a/helpers.py b/helpers.py
index 17301da..ce3ad69 100644
--- a/helpers.py
+++ b/helpers.py
@@ -1,4 +1,4 @@
-import sys, os, errno
+import sys, os, errno, fcntl
 import vars
 
 
@@ -69,3 +69,11 @@ def debug2(s):
         log_('redo: %s%s' % (vars.DEPTH, s))
 
 
+def close_on_exec(fd, yes):
+    fl = fcntl.fcntl(fd, fcntl.F_GETFD)
+    fl &= ~fcntl.FD_CLOEXEC
+    if yes:
+        fl |= fcntl.FD_CLOEXEC
+    fcntl.fcntl(fd, fcntl.F_SETFD, fl)
+
+
diff --git a/state.py b/state.py
index 4e4da25..4a5ad18 100644
--- a/state.py
+++ b/state.py
@@ -1,6 +1,6 @@
 import sys, os, errno, glob
 import vars
-from helpers import unlink, debug2, mkdirp
+from helpers import unlink, debug2, mkdirp, close_on_exec
 
 
 def init():
@@ -145,8 +145,8 @@ def start(t):
 class Lock:
     def __init__(self, t):
         self.owned = False
+        self.rfd = self.wfd = None
         self.lockname = _sname('lock', t)
-        self.tmpname = _sname('lock%d' % os.getpid(), t)
 
     def __del__(self):
         if self.owned:
@@ -156,6 +156,10 @@ class Lock:
         try:
             os.mkfifo(self.lockname, 0600)
             self.owned = True
+            self.rfd = os.open(self.lockname, os.O_RDONLY|os.O_NONBLOCK)
+            self.wfd = os.open(self.lockname, os.O_WRONLY)
+            close_on_exec(self.rfd, True)
+            close_on_exec(self.wfd, True)
         except OSError, e:
             if e.errno == errno.EEXIST:
                 pass
@@ -172,22 +176,11 @@ class Lock:
         if not self.owned:
             raise Exception("can't unlock %r - we don't own it" 
                             % self.lockname)
-        # make sure no readers can connect
-        try:
-            os.rename(self.lockname, self.tmpname)
-        except OSError, e:
-            if e.errno == errno.ENOENT: # 'make clean' might do this
-                self.owned = False
-                return
-        try:
-            # ping any connected readers
-            os.close(os.open(self.tmpname, os.O_WRONLY|os.O_NONBLOCK))
-        except OSError, e:
-            if e.errno == errno.ENXIO: # no readers open; that's ok
-                pass
-            else:
-                raise
-        os.unlink(self.tmpname)
+        unlink(self.lockname)
+        # ping any connected readers
+        os.close(self.rfd)
+        os.close(self.wfd)
+        self.rfd = self.wfd = None
         self.owned = False
 
     def wait(self):
@@ -195,7 +188,11 @@ class Lock:
             raise Exception("can't wait on %r - we own it" % self.lockname)
         try:
             # open() will finish only when a writer exists and does close()
-            os.close(os.open(self.lockname, os.O_RDONLY))
+            fd = os.open(self.lockname, os.O_RDONLY)
+            try:
+                os.read(fd, 1)
+            finally:
+                os.close(fd)
         except OSError, e:
             if e.errno == errno.ENOENT:
                 pass  # it's not even unlocked or was unlocked earlier