[utils] add SharedLockPool for HDFFile

tomoscan/utils.py

@@ -30,6 +30,8 @@ __date__ = "02/10/2017"
 
 
 import functools
+from contextlib import contextmanager, ExitStack
+import threading
 
 
 def _docstring(dest, origin):
@@ -65,3 +67,55 @@ def docstring(origin):
         If the origin class has not method n case the
     """
     return functools.partial(_docstring, origin=origin)
+
+
+class SharedLockPool:
+    """
+    Allows to acquire locks identified by name (hashable type) recursively.
+    """
+
+    def __init__(self):
+        self.__locks = {}
+        self.__locks_mutex = threading.Semaphore(value=1)
+
+    def __len__(self):
+        return len(self.__locks)
+
+    @property
+    def names(self):
+        return list(self.__locks.keys())
+
+    @contextmanager
+    def _modify_locks(self):
+        self.__locks_mutex.acquire()
+        try:
+            yield self.__locks
+        finally:
+            self.__locks_mutex.release()
+
+    @contextmanager
+    def acquire(self, name):
+        with self._modify_locks() as locks:
+            lock = locks.get(name, None)
+            if lock is None:
+                locks[name] = lock = threading.RLock()
+        lock.acquire()
+        try:
+            yield
+        finally:
+            lock.release()
+            with self._modify_locks() as locks:
+                locks.pop(name)
+
+    @contextmanager
+    def acquire_context_creation(self, name, contextmngr, *args, **kwargs):
+        """
+        Acquire lock only during context creation.
+
+        This can be used for example to protect the opening of a file
+        but not hold the lock while the file is open.
+        """
+        with ExitStack() as stack:
+            with self.acquire(name):
+                ret = stack.enter_context(contextmngr(*args, **kwargs))
+            yield ret