Concurrency refactor 999 (#1029)

* Working on making export threadsafe, #999

* Working on making export threadsafe, #999

* refactor for concurrent export, #999

* Fixed race condition in ExportRecord context manager

tests/test_concurrent_export.py

@@ -0,0 +1,66 @@
+""""Test that PhotoInfo.export can export concurrently"""
+
+import concurrent.futures
+import pathlib
+import sqlite3
+import tempfile
+
+import pytest
+
+import osxphotos
+
+PHOTOS_DB = "tests/Test-10.15.7.photoslibrary"
+
+
+@pytest.mark.skipif(sqlite3.threadsafety != 3, reason="sqlite3 not threadsafe")
+@pytest.mark.parametrize(
+    "count", range(10)
+)  # repeat multiple times to try to catch any concurrency errors
+def test_concurrent_export(count):
+    """Test that PhotoInfo.export can export concurrently"""
+    photosdb = osxphotos.PhotosDB(dbfile=PHOTOS_DB)
+    photos = [p for p in photosdb.photos() if not p.ismissing]
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        with concurrent.futures.ThreadPoolExecutor(max_workers=8) as executor:
+            futures = [
+                executor.submit(p.export, tmpdir, f"{p.uuid}_{p.original_filename}")
+                for p in photos
+            ]
+            exported = []
+            for future in concurrent.futures.as_completed(futures):
+                exported.extend(future.result())
+    assert len(exported) == len(photos)
+
+
+@pytest.mark.skipif(sqlite3.threadsafety != 3, reason="sqlite3 not threadsafe")
+@pytest.mark.parametrize(
+    "count", range(10)
+)  # repeat multiple times to try to catch any concurrency errors
+def test_concurrent_export_with_exportdb(count):
+    """Test that PhotoInfo.export can export concurrently"""
+    photosdb = osxphotos.PhotosDB(dbfile=PHOTOS_DB)
+    photos = [p for p in photosdb.photos() if not p.ismissing]
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        exportdb = osxphotos.ExportDB(pathlib.Path(tmpdir) / "export.db", tmpdir)
+        with concurrent.futures.ThreadPoolExecutor(max_workers=8) as executor:
+            futures = []
+            for p in photos:
+                options = osxphotos.ExportOptions()
+                options.export_db = exportdb
+                exporter = osxphotos.PhotoExporter(p)
+                futures.append(
+                    executor.submit(
+                        exporter.export,
+                        tmpdir,
+                        f"{p.uuid}_{p.original_filename}",
+                        options=options,
+                    )
+                )
+            export_results = osxphotos.photoexporter.ExportResults()
+            for future in concurrent.futures.as_completed(futures):
+                export_results += future.result()
+
+    assert len(export_results.exported) == len(photos)
+    assert len(list(exportdb.get_exported_files())) == len(photos)