fix race condition as reported by Ralf Schmitt

CHANGELOG

@@ -5,6 +5,9 @@
 
 - fix issue34 - distributed testing with -p plugin now works correctly
 
+- fix race condition in looponfail mode where a concurrent file removal
+  could cause a crash
+
 1.5
 -------------------------
 

testing/test_looponfail.py

@@ -14,11 +14,11 @@ class TestStatRecorder:
         changed = sd.check()
         assert changed
 
-        tmp.ensure("new.py")
+        p = tmp.ensure("new.py")
         changed = sd.check()
         assert changed
 
-        tmp.join("new.py").remove()
+        p.remove()
         changed = sd.check()
         assert changed
 
@@ -36,6 +36,24 @@ class TestStatRecorder:
         changed = sd.check()
         assert changed
 
+    def test_filechange_deletion_race(self, tmpdir, monkeypatch):
+        tmp = tmpdir
+        sd = StatRecorder([tmp])
+        changed = sd.check()
+        assert not changed
+
+        p = tmp.ensure("new.py")
+        changed = sd.check()
+        assert changed
+
+        p.remove()
+        # make check()'s visit() call return our just removed
+        # path as if we were in a race condition
+        monkeypatch.setattr(tmp, 'visit', lambda *args: [p])
+
+        changed = sd.check()
+        assert changed
+
     def test_pycremoval(self, tmpdir):
         tmp = tmpdir
         hello = tmp.ensure("hello.py")

xdist/looponfail.py

@@ -201,14 +201,11 @@ class StatRecorder:
         newstat = {}
         for rootdir in self.rootdirlist:
             for path in rootdir.visit(self.fil, self.rec):
-                oldstat = statcache.get(path, None)
-                if oldstat is not None:
-                    del statcache[path]
+                oldstat = statcache.pop(path, None)
                 try:
                     newstat[path] = curstat = path.stat()
                 except py.error.ENOENT:
                     if oldstat:
-                        del statcache[path]
                         changed = True
                 else:
                     if oldstat: