Changes needed to be able to use doctr on AWS Lambda

docs/source/index.rst

@@ -74,6 +74,7 @@ Supported datasets
    using_doctr/using_datasets
    using_doctr/sharing_models
    using_doctr/using_model_export
+   using_doctr/running_on_aws
 
 
 .. toctree::

docs/source/using_doctr/running_on_aws.rst

@@ -0,0 +1,7 @@
+AWS Lambda
+========================
+
+AWS Lambda's (read more about Lambda https://aws.amazon.com/lambda/) security policy does not allow you to write anywhere outside `/tmp` directory.
+There are two things you need to do to make `doctr` work on lambda:
+1. Disable usage of `multiprocessing` package by setting `DOCTR_MULTIPROCESSING_DISABLE` enivronment variable to `TRUE`. You need to do this, because this package uses `/dev/shm` directory for shared memory.
+2. Change directory `doctr` uses for caching models. By default it's `~/.cache/doctr` which is outside of `/tmp` on AWS Lambda'. You can do this by setting `DOCTR_CACHE_DIR` enivronment variable.

doctr/datasets/datasets/base.py

@@ -92,8 +92,12 @@ def __init__(
         cache_subdir: Optional[str] = None,
         **kwargs: Any,
     ) -> None:
+        cache_dir = (
+            str(os.environ.get("DOCTR_CACHE_DIR", os.path.join(os.path.expanduser("~"), ".cache", "doctr")))
+            if cache_dir is None
+            else cache_dir
+        )
 
-        cache_dir = os.path.join(os.path.expanduser("~"), ".cache", "doctr") if cache_dir is None else cache_dir
         cache_subdir = "datasets" if cache_subdir is None else cache_subdir
 
         file_name = file_name if isinstance(file_name, str) else os.path.basename(url)

doctr/utils/data.py

@@ -64,13 +64,19 @@ def download_from_url(
 
     Returns:
         the location of the downloaded file
+
+    Note:
+        You can change cache directory location by using `DOCTR_CACHE_DIR` environment variable.
     """
 
     if not isinstance(file_name, str):
         file_name = url.rpartition("/")[-1]
 
-    if not isinstance(cache_dir, str):
-        cache_dir = os.path.join(os.path.expanduser("~"), ".cache", "doctr")
+    cache_dir = (
+        str(os.environ.get("DOCTR_CACHE_DIR", os.path.join(os.path.expanduser("~"), ".cache", "doctr")))
+        if cache_dir is None
+        else cache_dir
+    )
 
     # Check hash in file name
     if hash_prefix is None:
@@ -84,8 +90,19 @@ def download_from_url(
         logging.info(f"Using downloaded & verified file: {file_path}")
         return file_path
 
-    # Create folder hierarchy
-    folder_path.mkdir(parents=True, exist_ok=True)
+    try:
+        # Create folder hierarchy
+        folder_path.mkdir(parents=True, exist_ok=True)
+    except OSError:
+        error_message = f"Failed creating cache direcotry at {folder_path}"
+        if os.environ.get("DOCTR_CACHE_DIR", ""):
+            error_message += " using path from 'DOCTR_CACHE_DIR' environment variable."
+        else:
+            error_message += (
+                ". You can change default cache directory using 'DOCTR_CACHE_DIR' environment variable if needed."
+            )
+        logging.error(error_message)
+        raise
     # Download the file
     try:
         print(f"Downloading {url} to {file_path}")

doctr/utils/multithreading.py

@@ -5,9 +5,12 @@
 
 
 import multiprocessing as mp
+import os
 from multiprocessing.pool import ThreadPool
 from typing import Any, Callable, Iterable, Iterator, Optional
 
+from doctr.file_utils import ENV_VARS_TRUE_VALUES
+
 __all__ = ["multithread_exec"]
 
 
@@ -25,11 +28,16 @@ def multithread_exec(func: Callable[[Any], Any], seq: Iterable[Any], threads: Op
 
     Returns:
         iterator of the function's results using the iterable as inputs
+
+    Notes:
+        This function uses ThreadPool from multiprocessing package, which uses `/dev/shm` directory for shared memory.
+        If you do not have write permissions for this directory (if you run `doctr` on AWS Lambda for instance),
+        you might want to disable multiprocessing. To achieve that, set 'DOCTR_MULTIPROCESSING_DISABLE' to 'TRUE'.
     """
 
     threads = threads if isinstance(threads, int) else min(16, mp.cpu_count())
     # Single-thread
-    if threads < 2:
+    if threads < 2 or os.environ.get("DOCTR_MULTIPROCESSING_DISABLE", "").upper() in ENV_VARS_TRUE_VALUES:
         results = map(func, seq)
     # Multi-threading
     else:

tests/common/test_utils_data.py

@@ -0,0 +1,46 @@
+import os
+from pathlib import PosixPath
+from unittest.mock import patch
+
+import pytest
+
+from doctr.utils.data import download_from_url
+
+
+@patch("doctr.utils.data._urlretrieve")
+@patch("pathlib.Path.mkdir")
+@patch.dict(os.environ, {"HOME": "/"}, clear=True)
+def test_download_from_url(mkdir_mock, urlretrieve_mock):
+    download_from_url("test_url")
+    urlretrieve_mock.assert_called_with("test_url", PosixPath("/.cache/doctr/test_url"))
+
+
+@patch.dict(os.environ, {"DOCTR_CACHE_DIR": "/test"}, clear=True)
+@patch("doctr.utils.data._urlretrieve")
+@patch("pathlib.Path.mkdir")
+def test_download_from_url_customizing_cache_dir(mkdir_mock, urlretrieve_mock):
+    download_from_url("test_url")
+    urlretrieve_mock.assert_called_with("test_url", PosixPath("/test/test_url"))
+
+
+@patch.dict(os.environ, {"HOME": "/"}, clear=True)
+@patch("pathlib.Path.mkdir", side_effect=OSError)
+@patch("logging.error")
+def test_download_from_url_error_creating_directory(logging_mock, mkdir_mock):
+    with pytest.raises(OSError):
+        download_from_url("test_url")
+    logging_mock.assert_called_with(
+        "Failed creating cache direcotry at /.cache/doctr."
+        " You can change default cache directory using 'DOCTR_CACHE_DIR' environment variable if needed."
+    )
+
+
+@patch.dict(os.environ, {"HOME": "/", "DOCTR_CACHE_DIR": "/test"}, clear=True)
+@patch("pathlib.Path.mkdir", side_effect=OSError)
+@patch("logging.error")
+def test_download_from_url_error_creating_directory_with_env_var(logging_mock, mkdir_mock):
+    with pytest.raises(OSError):
+        download_from_url("test_url")
+    logging_mock.assert_called_with(
+        "Failed creating cache direcotry at /test using path from 'DOCTR_CACHE_DIR' environment variable."
+    )

tests/common/test_utils_multithreading.py

@@ -1,3 +1,7 @@
+import os
+from multiprocessing.pool import ThreadPool
+from unittest.mock import patch
+
 import pytest
 
 from doctr.utils.multithreading import multithread_exec
@@ -18,3 +22,10 @@
 def test_multithread_exec(input_seq, func, output_seq):
     assert list(multithread_exec(func, input_seq)) == output_seq
     assert list(multithread_exec(func, input_seq, 0)) == output_seq
+
+
+@patch.dict(os.environ, {"DOCTR_MULTIPROCESSING_DISABLE": "TRUE"}, clear=True)
+def test_multithread_exec_multiprocessing_disable():
+    with patch.object(ThreadPool, "map") as mock_tp_map:
+        multithread_exec(lambda x: x, [1, 2])
+    assert not mock_tp_map.called