WIP: Zarr backend

xarray/backends/common.py

@@ -164,9 +164,10 @@ def __exit__(self, exception_type, exception_value, traceback):
 
 
 class ArrayWriter(object):
-    def __init__(self):
+    def __init__(self, lock=GLOBAL_LOCK):
         self.sources = []
         self.targets = []
+        self.lock = lock
 
     def add(self, source, target):
         if isinstance(source, dask_array_type):
@@ -184,7 +185,7 @@ def sync(self):
             import dask.array as da
             import dask
             if LooseVersion(dask.__version__) > LooseVersion('0.8.1'):
-                da.store(self.sources, self.targets, lock=GLOBAL_LOCK)
+                da.store(self.sources, self.targets, lock=self.lock)
             else:
                 da.store(self.sources, self.targets)
             self.sources = []

xarray/backends/zarr.py

@@ -10,7 +10,7 @@
 from ..core import indexing
 from ..core.utils import FrozenOrderedDict, HiddenKeyDict
 from ..core.pycompat import iteritems, OrderedDict, integer_types
-from .common import (AbstractWritableDataStore, BackendArray)
+from .common import AbstractWritableDataStore, BackendArray, ArrayWriter
 from .. import conventions
 
 # need some special secret attributes to tell us the dimensions
@@ -298,8 +298,15 @@ def __init__(self, zarr_group, mode='r', synchronizer=None, group=None,
         if _DIMENSION_KEY not in self.ds.attrs:
             self.ds.attrs[_DIMENSION_KEY] = {}
 
+        if writer is None:
+            # by default, we should not need a lock for writing zarr because
+            # we do not (yet) allow overlapping chunks during write
+            zarr_writer = ArrayWriter(lock=None)
+        else:
+            zarr_writer = writer
+
         # do we need to define attributes for all of the opener keyword args?
-        super(ZarrStore, self).__init__(writer)
+        super(ZarrStore, self).__init__(zarr_writer)
 
     def open_store_variable(self, name, zarr_array):
         data = indexing.LazilyIndexedArray(ZarrArrayWrapper(name, self))