RF: Write DFT database manager as object

nibabel/dft.py

@@ -11,6 +11,7 @@
 """
 
 
+import contextlib
 import os
 from os.path import join as pjoin
 import tempfile
@@ -74,7 +75,7 @@ def __getattribute__(self, name):
         val = object.__getattribute__(self, name)
         if name == 'series' and val is None:
             val = []
-            with _db_nochange() as c:
+            with DB.readonly_cursor() as c:
                 c.execute("SELECT * FROM series WHERE study = ?", (self.uid, ))
                 cols = [el[0] for el in c.description]
                 for row in c:
@@ -106,7 +107,7 @@ def __getattribute__(self, name):
         val = object.__getattribute__(self, name)
         if name == 'storage_instances' and val is None:
             val = []
-            with _db_nochange() as c:
+            with DB.readonly_cursor() as c:
                 query = """SELECT *
                              FROM storage_instance
                             WHERE series = ?
@@ -227,7 +228,7 @@ def __init__(self, d):
     def __getattribute__(self, name):
         val = object.__getattribute__(self, name)
         if name == 'files' and val is None:
-            with _db_nochange() as c:
+            with DB.readonly_cursor() as c:
                 query = """SELECT directory, name
                              FROM file
                             WHERE storage_instance = ?
@@ -241,34 +242,6 @@ def dicom(self):
         return pydicom.read_file(self.files[0])
 
 
-class _db_nochange:
-    """context guard for read-only database access"""
-
-    def __enter__(self):
-        self.c = DB.cursor()
-        return self.c
-
-    def __exit__(self, type, value, traceback):
-        if type is None:
-            self.c.close()
-        DB.rollback()
-
-
-class _db_change:
-    """context guard for database access requiring a commit"""
-
-    def __enter__(self):
-        self.c = DB.cursor()
-        return self.c
-
-    def __exit__(self, type, value, traceback):
-        if type is None:
-            self.c.close()
-            DB.commit()
-        else:
-            DB.rollback()
-
-
 def _get_subdirs(base_dir, files_dict=None, followlinks=False):
     dirs = []
     for (dirpath, dirnames, filenames) in os.walk(base_dir, followlinks=followlinks):
@@ -288,7 +261,7 @@ def update_cache(base_dir, followlinks=False):
     for d in dirs:
         os.stat(d)
         mtimes[d] = os.stat(d).st_mtime
-    with _db_nochange() as c:
+    with DB.readwrite_cursor() as c:
         c.execute("SELECT path, mtime FROM directory")
         db_mtimes = dict(c)
         c.execute("SELECT uid FROM study")
@@ -297,7 +270,6 @@ def update_cache(base_dir, followlinks=False):
         series = [row[0] for row in c]
         c.execute("SELECT uid FROM storage_instance")
         storage_instances = [row[0] for row in c]
-    with _db_change() as c:
         for dir in sorted(mtimes.keys()):
             if dir in db_mtimes and mtimes[dir] <= db_mtimes[dir]:
                 continue
@@ -316,7 +288,7 @@ def get_studies(base_dir=None, followlinks=False):
     if base_dir is not None:
         update_cache(base_dir, followlinks)
     if base_dir is None:
-        with _db_nochange() as c:
+        with DB.readonly_cursor() as c:
             c.execute("SELECT * FROM study")
             studies = []
             cols = [el[0] for el in c.description]
@@ -331,7 +303,7 @@ def get_studies(base_dir=None, followlinks=False):
                                WHERE uid IN (SELECT storage_instance
                                                FROM file
                                               WHERE directory = ?))"""
-    with _db_nochange() as c:
+    with DB.readonly_cursor() as c:
         study_uids = {}
         for dir in _get_subdirs(base_dir, followlinks=followlinks):
             c.execute(query, (dir, ))
@@ -443,7 +415,7 @@ def _update_file(c, path, fname, studies, series, storage_instances):
 
 
 def clear_cache():
-    with _db_change() as c:
+    with DB.readwrite_cursor() as c:
         c.execute("DELETE FROM file")
         c.execute("DELETE FROM directory")
         c.execute("DELETE FROM storage_instance")
@@ -478,26 +450,64 @@ def clear_cache():
                           mtime INTEGER NOT NULL,
                           storage_instance TEXT DEFAULT NULL REFERENCES storage_instance,
                           PRIMARY KEY (directory, name))""")
-DB_FNAME = pjoin(tempfile.gettempdir(), f'dft.{getpass.getuser()}.sqlite')
-DB = None
 
 
-def _init_db(verbose=True):
-    """ Initialize database """
-    if verbose:
-        logger.info('db filename: ' + DB_FNAME)
-    global DB
-    DB = sqlite3.connect(DB_FNAME, check_same_thread=False)
-    with _db_change() as c:
-        c.execute("SELECT COUNT(*) FROM sqlite_master WHERE type = 'table'")
-        if c.fetchone()[0] == 0:
-            logger.debug('create')
-            for q in CREATE_QUERIES:
-                c.execute(q)
+class _DB:
+    def __init__(self, fname=None, verbose=True):
+        self.fname = fname or pjoin(tempfile.gettempdir(), f'dft.{getpass.getuser()}.sqlite')
+        self.verbose = verbose
+
+    @property
+    def session(self):
+        """Get sqlite3 Connection
+
+        The connection is created on the first call of this property
+        """
+        try:
+            return self._session
+        except AttributeError:
+            self._init_db()
+            return self._session
+
+    def _init_db(self):
+        if self.verbose:
+            logger.info('db filename: ' + self.fname)
+
+        self._session = sqlite3.connect(self.fname, isolation_level="EXCLUSIVE")
+        with self.readwrite_cursor() as c:
+            c.execute("SELECT COUNT(*) FROM sqlite_master WHERE type = 'table'")
+            if c.fetchone()[0] == 0:
+                logger.debug('create')
+                for q in CREATE_QUERIES:
+                    c.execute(q)
+
+    def __repr__(self):
+        return f"<DFT {self.fname!r}>"
+
+    @contextlib.contextmanager
+    def readonly_cursor(self):
+        cursor = self.session.cursor()
+        try:
+            yield cursor
+        finally:
+            cursor.close()
+            self.session.rollback()
+
+    @contextlib.contextmanager
+    def readwrite_cursor(self):
+        cursor = self.session.cursor()
+        try:
+            yield cursor
+        except Exception:
+            self.session.rollback()
+            raise
+        finally:
+            cursor.close()
+        self.session.commit()
 
 
+DB = None
 if os.name == 'nt':
     warnings.warn('dft needs FUSE which is not available for windows')
 else:
-    _init_db()
-# eof
+    DB = _DB()

nibabel/tests/test_dft.py

@@ -5,6 +5,7 @@
 from os.path import join as pjoin, dirname
 from io import BytesIO
 from ..testing import suppress_warnings
+import sqlite3
 
 with suppress_warnings():
     from .. import dft
@@ -29,26 +30,57 @@ def setUpModule():
         raise unittest.SkipTest('Need pydicom for dft tests, skipping')
 
 
-def test_init():
+class Test_DBclass:
+    """Some tests on the database manager class that don't get exercised through the API"""
+    def setup_method(self):
+        self._db = dft._DB(fname=":memory:", verbose=False)
+
+    def test_repr(self):
+        assert repr(self._db) == "<DFT ':memory:'>"
+
+    def test_cursor_conflict(self):
+        rwc = self._db.readwrite_cursor
+        statement = ("INSERT INTO directory (path, mtime) VALUES (?, ?)", ("/tmp", 0))
+        with pytest.raises(sqlite3.IntegrityError):
+            # Whichever exits first will commit and make the second violate uniqueness
+            with rwc() as c1, rwc() as c2:
+                c1.execute(*statement)
+                c2.execute(*statement)
+
+
+@pytest.fixture
+def db(monkeypatch):
+    """Build a dft database in memory to avoid cross-process races
+    and not modify the host filesystem."""
+    database = dft._DB(fname=":memory:")
+    monkeypatch.setattr(dft, "DB", database)
+    yield database
+
+
+def test_init(db):
     dft.clear_cache()
     dft.update_cache(data_dir)
+    # Verify a second update doesn't crash
+    dft.update_cache(data_dir)
 
 
-def test_study():
-    studies = dft.get_studies(data_dir)
-    assert len(studies) == 1
-    assert (studies[0].uid ==
-                 '1.3.12.2.1107.5.2.32.35119.30000010011408520750000000022')
-    assert studies[0].date == '20100114'
-    assert studies[0].time == '121314.000000'
-    assert studies[0].comments == 'dft study comments'
-    assert studies[0].patient_name == 'dft patient name'
-    assert studies[0].patient_id == '1234'
-    assert studies[0].patient_birth_date == '19800102'
-    assert studies[0].patient_sex == 'F'
-
-
-def test_series():
+def test_study(db):
+    # First pass updates the cache, second pass reads it out
+    for base_dir in (data_dir, None):
+        studies = dft.get_studies(base_dir)
+        assert len(studies) == 1
+        assert (studies[0].uid ==
+                     '1.3.12.2.1107.5.2.32.35119.30000010011408520750000000022')
+        assert studies[0].date == '20100114'
+        assert studies[0].time == '121314.000000'
+        assert studies[0].comments == 'dft study comments'
+        assert studies[0].patient_name == 'dft patient name'
+        assert studies[0].patient_id == '1234'
+        assert studies[0].patient_birth_date == '19800102'
+        assert studies[0].patient_sex == 'F'
+
+
+def test_series(db):
     studies = dft.get_studies(data_dir)
     assert len(studies[0].series) == 1
     ser = studies[0].series[0]
@@ -62,7 +94,7 @@ def test_series():
     assert ser.bits_stored == 12
 
 
-def test_storage_instances():
+def test_storage_instances(db):
     studies = dft.get_studies(data_dir)
     sis = studies[0].series[0].storage_instances
     assert len(sis) == 2
@@ -74,19 +106,15 @@ def test_storage_instances():
                  '1.3.12.2.1107.5.2.32.35119.2010011420300180088599504.1')
 
 
-def test_storage_instance():
-    pass
-
-
 @unittest.skipUnless(have_pil, 'could not import PIL.Image')
-def test_png():
+def test_png(db):
     studies = dft.get_studies(data_dir)
     data = studies[0].series[0].as_png()
     im = PImage.open(BytesIO(data))
     assert im.size == (256, 256)
 
 
-def test_nifti():
+def test_nifti(db):
     studies = dft.get_studies(data_dir)
     data = studies[0].series[0].as_nifti()
     assert len(data) == 352 + 2 * 256 * 256 * 2