Here is my model definition
class Item(models.Model):
name = models.CharField(max_length=256)
def item_id_path(instance, filename):
return '{}/{}'.format(instance.item.id, filename)
# Create your models here.
class File(models.Model):
file = models.FileField(upload_to=item_id_path)
timestamp = models.DateTimeField(auto_now_add=True)
item = models.ForeignKey(Item, on_delete=models.CASCADE)
def __str__(self):
return self.file.name
The application posts multiples file that belong to the same item. But I
run into race condition in making directories. My server stores all the
related files in a separate folder (named by the item id) together.
In django/core/files/storage.py _save method it checks the existence of
uploading directory. When multiple files for the same item are uploaded the
first request checks the existence of the directory and is going to create
one, then it switches to the second file upload. It also finds that the
directory doesn't exist yet and it is going to do the same directory
creation. The second file upload will fail because the first file upload
has already created the folder. It fails at the last line of the following
code snippet in storage.py.
def _save(self, name, content):
full_path = self.path(name)
# Create any intermediate directories that do not exist.
directory = os.path.dirname(full_path)
if not os.path.exists(directory):
try:
if self.directory_permissions_mode is not None:
# os.makedirs applies the global umask, so we reset it,
# for consistency with file_permissions_mode behavior.
old_umask = os.umask(0)
try:
os.makedirs(directory, self.directory_permissions_mode)
finally:
os.umask(old_umask)
else:
os.makedirs(directory)
what approach can I take to avoid this race condition?
I guess changing the source code from os.makedirs(directory) to
os.makedirs(directory, exist_ok=True) could work.
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/rest_framework/mixins.py",
line 21, in create
self.perform_create(serializer)
File "/Users/han/projects/django_maplus_server/rest_api/views.py", line
27, in perform_create
return super(FileViewSet, self).perform_create(serializer)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/rest_framework/mixins.py",
line 26, in perform_create
serializer.save()
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/rest_framework/serializers.py",
line 214, in save
self.instance = self.create(validated_data)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/rest_framework/serializers.py",
line 940, in create
instance = ModelClass.objects.create(**validated_data)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/manager.py",
line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/query.py",
line 413, in create
obj.save(force_insert=True, using=self.db)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/base.py",
line 717, in save
force_update=force_update, update_fields=update_fields)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/base.py",
line 747, in save_base
updated = self._save_table(raw, cls, force_insert, force_update, using,
update_fields)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/base.py",
line 830, in _save_table
result = self._do_insert(cls._base_manager, using, fields, update_pk,
raw)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/base.py",
line 868, in _do_insert
using=using, raw=raw)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/manager.py",
line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/query.py",
line 1133, in _insert
return query.get_compiler(using=using).execute_sql(return_id)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/sql/compiler.py",
line 1284, in execute_sql
for sql, params in self.as_sql():
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/sql/compiler.py",
line 1237, in as_sql
for obj in self.query.objs
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/sql/compiler.py",
line 1237, in <listcomp>
for obj in self.query.objs
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/sql/compiler.py",
line 1236, in <listcomp>
[self.prepare_value(field, self.pre_save_val(field, obj)) for field in
fields]
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/sql/compiler.py",
line 1188, in pre_save_val
return field.pre_save(obj, add=True)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/fields/files.py",
line 288, in pre_save
file.save(file.name, file.file, save=False)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/db/models/fields/files.py",
line 87, in save
self.name = self.storage.save(name, content,
max_length=self.field.max_length)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/core/files/storage.py",
line 49, in save
return self._save(name, content)
File
"/Users/han/anaconda3/envs/django/lib/python3.6/site-packages/django/core/files/storage.py",
line 236, in _save
os.makedirs(directory)
File "/Users/han/anaconda3/envs/django/lib/python3.6/os.py", line 220, in
makedirs
mkdir(name, mode)
FileExistsError: [Errno 17] File exists:
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