diff --git a/mercurial/vfs.py b/mercurial/vfs.py
--- a/mercurial/vfs.py
+++ b/mercurial/vfs.py
@@ -269,6 +269,8 @@
         for dirpath, dirs, files in os.walk(self.join(path), onerror=onerror):
             yield (dirpath[prefixlen:], dirs, files)
 
+    threaddata = threading.local()
+
     @contextlib.contextmanager
     def backgroundclosing(self, ui, expectedcount=-1):
         """Allow files to be closed asynchronously.
@@ -277,19 +279,17 @@
         to ``__call__``/``open`` to result in the file possibly being closed
         asynchronously, on a background thread.
         """
-        # This is an arbitrary restriction and could be changed if we ever
-        # have a use case.
         vfs = getattr(self, 'vfs', self)
-        if getattr(vfs, '_backgroundfilecloser', None):
+        if getattr(vfs.threaddata, '_backgroundfilecloser', None):
             raise error.Abort(
-                _('can only have 1 active background file closer'))
+                _('can only have 1 active background file closer per thread'))
 
         with backgroundfilecloser(ui, expectedcount=expectedcount) as bfc:
             try:
-                vfs._backgroundfilecloser = bfc
+                vfs.threaddata._backgroundfilecloser = bfc
                 yield bfc
             finally:
-                vfs._backgroundfilecloser = None
+                vfs.threaddata._backgroundfilecloser = None
 
 class vfs(abstractvfs):
     '''Operate files relative to a base directory
@@ -414,12 +414,12 @@
             fp = checkambigatclosing(fp)
 
         if backgroundclose:
-            if not self._backgroundfilecloser:
+            if not self.threaddata._backgroundfilecloser:
                 raise error.Abort(_('backgroundclose can only be used when a '
                                   'backgroundclosing context manager is active')
                                   )
 
-            fp = delayclosedfile(fp, self._backgroundfilecloser)
+            fp = delayclosedfile(fp, self.threaddata._backgroundfilecloser)
 
         return fp