[Parallel] Avoid race condition when downloading vocab (#1078)

* use os.replace

* Update files.py

* Update utils.py

Author: eric-haibin-lin

src/gluonnlp/data/utils.py

@@ -17,17 +17,19 @@
 
 """Utility classes and functions. They help organize and keep statistics of datasets."""
 import collections
-import errno
 import os
 import tarfile
 import zipfile
-import time
+import random
+import sys
+import shutil
 
 import numpy as np
 from mxnet.gluon.data import SimpleDataset
 from mxnet.gluon.utils import _get_repo_url, check_sha1, download
 
 from .. import _constants as C
+from .. import utils
 
 __all__ = [
     'Counter', 'count_tokens', 'concat_sequence', 'slice_sequence', 'train_valid_split',
@@ -303,6 +305,11 @@ def _load_pretrained_vocab(name, root, cls=None):
     root = os.path.expanduser(root)
     file_path = os.path.join(root, file_name + '.vocab')
     sha1_hash = _vocab_sha1[name]
+
+    temp_num = str(random.Random().randint(1, sys.maxsize))
+    temp_root = os.path.join(root, temp_num)
+    temp_file_path = os.path.join(temp_root, file_name + '.vocab')
+    temp_zip_file_path = os.path.join(root, temp_num + file_name + '.zip')
     if os.path.exists(file_path):
         if check_sha1(file_path, sha1_hash):
             return _load_vocab_file(file_path, cls)
@@ -311,34 +318,19 @@ def _load_pretrained_vocab(name, root, cls=None):
     else:
         print('Vocab file is not found. Downloading.')
 
-    if not os.path.exists(root):
-        try:
-            os.makedirs(root)
-        except OSError as e:
-            if e.errno == errno.EEXIST and os.path.isdir(root):
-                pass
-            else:
-                raise e
+    utils.mkdir(root)
 
-    prefix = str(time.time())
-    zip_file_path = os.path.join(root, prefix + file_name + '.zip')
     repo_url = _get_repo_url()
     if repo_url[-1] != '/':
         repo_url = repo_url + '/'
     download(_url_format.format(repo_url=repo_url, file_name=file_name),
-             path=zip_file_path,
-             overwrite=True)
-    with zipfile.ZipFile(zip_file_path) as zf:
+             path=temp_zip_file_path, overwrite=True)
+    with zipfile.ZipFile(temp_zip_file_path) as zf:
         if not os.path.exists(file_path):
-            zf.extractall(root)
-    try:
-        os.remove(zip_file_path)
-    except OSError as e:
-        # file has already been removed.
-        if e.errno == 2:
-            pass
-        else:
-            raise e
+            utils.mkdir(temp_root)
+            zf.extractall(temp_root)
+            os.replace(temp_file_path, file_path)
+            shutil.rmtree(temp_root)
 
     if check_sha1(file_path, sha1_hash):
         return _load_vocab_file(file_path, cls)

src/gluonnlp/utils/files.py

@@ -17,7 +17,7 @@
 # pylint:disable=redefined-outer-name,logging-format-interpolation
 """Utility functions for files."""
 
-__all__ = ['mkdir', 'glob']
+__all__ = ['mkdir', 'glob', 'remove']
 
 import os
 import warnings
@@ -45,8 +45,28 @@ def glob(url, separator=','):
         result.extend(_glob.glob(os.path.expanduser(pattern.strip())))
     return result
 
+def remove(filename):
+    """Remove a file
+
+    Parameters
+    ----------
+    filename : str
+        The name of the target file to remove
+    """
+    if C.S3_PREFIX in filename:
+        msg = 'Removing objects on S3 is not supported: {}'.format(filename)
+        raise NotImplementedError(msg)
+    try:
+        os.remove(filename)
+    except OSError as e:
+        # file has already been removed.
+        if e.errno == 2:
+            pass
+        else:
+            raise e
+
 def mkdir(dirname):
-    """Create directory.
+    """Create a directory.
 
     Parameters
     ----------

tests/unittest/test_datasets.py

@@ -21,6 +21,7 @@
 import io
 import random
 import warnings
+import threading
 
 from flaky import flaky
 import mxnet as mx
@@ -702,6 +703,7 @@ def test_numpy_dataset():
     (nlp.data.GlueMRPC, 'mrpc', 'dev', 408, 3),
     (nlp.data.GlueMRPC, 'mrpc', 'test', 1725, 2),
 ])
+
 @pytest.mark.serial
 @pytest.mark.remote_required
 def test_glue_data(cls, name, segment, length, fields):
@@ -713,3 +715,19 @@ def test_glue_data(cls, name, segment, length, fields):
 
     for i, x in enumerate(dataset):
         assert len(x) == fields, x
+
+@pytest.mark.serial
+@pytest.mark.remote_required
+def test_parallel_load_pretrained_vocab():
+    def fn(name):
+        root = 'test_parallel_load_pretrained_vocab'
+        _ = nlp.data.utils._load_pretrained_vocab(name, root=root)
+    threads = []
+    name = 'openwebtext_book_corpus_wiki_en_uncased'
+    for _ in range(10):
+        x = threading.Thread(target=fn, args=(name,))
+        threads.append(x)
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()