diff options
Diffstat (limited to 'Lib/importlib/_bootstrap.py')
| -rw-r--r-- | Lib/importlib/_bootstrap.py | 191 |
1 files changed, 178 insertions, 13 deletions
diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py index 41b96a9..3069bd8 100644 --- a/Lib/importlib/_bootstrap.py +++ b/Lib/importlib/_bootstrap.py @@ -159,6 +159,145 @@ def new_module(name): return type(_io)(name) +# Module-level locking ######################################################## + +# A dict mapping module names to weakrefs of _ModuleLock instances +_module_locks = {} +# A dict mapping thread ids to _ModuleLock instances +_blocking_on = {} + + +class _DeadlockError(RuntimeError): + pass + + +class _ModuleLock: + """A recursive lock implementation which is able to detect deadlocks + (e.g. thread 1 trying to take locks A then B, and thread 2 trying to + take locks B then A). + """ + + def __init__(self, name): + self.lock = _thread.allocate_lock() + self.wakeup = _thread.allocate_lock() + self.name = name + self.owner = None + self.count = 0 + self.waiters = 0 + + def has_deadlock(self): + # Deadlock avoidance for concurrent circular imports. + me = _thread.get_ident() + tid = self.owner + while True: + lock = _blocking_on.get(tid) + if lock is None: + return False + tid = lock.owner + if tid == me: + return True + + def acquire(self): + """ + Acquire the module lock. If a potential deadlock is detected, + a _DeadlockError is raised. + Otherwise, the lock is always acquired and True is returned. + """ + tid = _thread.get_ident() + _blocking_on[tid] = self + try: + while True: + with self.lock: + if self.count == 0 or self.owner == tid: + self.owner = tid + self.count += 1 + return True + if self.has_deadlock(): + raise _DeadlockError("deadlock detected by %r" % self) + if self.wakeup.acquire(False): + self.waiters += 1 + # Wait for a release() call + self.wakeup.acquire() + self.wakeup.release() + finally: + del _blocking_on[tid] + + def release(self): + tid = _thread.get_ident() + with self.lock: + if self.owner != tid: + raise RuntimeError("cannot release un-acquired lock") + assert self.count > 0 + self.count -= 1 + if self.count == 0: + self.owner = None + if self.waiters: + self.waiters -= 1 + self.wakeup.release() + + def __repr__(self): + return "_ModuleLock(%r) at %d" % (self.name, id(self)) + + +class _DummyModuleLock: + """A simple _ModuleLock equivalent for Python builds without + multi-threading support.""" + + def __init__(self, name): + self.name = name + self.count = 0 + + def acquire(self): + self.count += 1 + return True + + def release(self): + if self.count == 0: + raise RuntimeError("cannot release un-acquired lock") + self.count -= 1 + + def __repr__(self): + return "_DummyModuleLock(%r) at %d" % (self.name, id(self)) + + +# The following two functions are for consumption by Python/import.c. + +def _get_module_lock(name): + """Get or create the module lock for a given module name. + + Should only be called with the import lock taken.""" + lock = None + if name in _module_locks: + lock = _module_locks[name]() + if lock is None: + if _thread is None: + lock = _DummyModuleLock(name) + else: + lock = _ModuleLock(name) + def cb(_): + del _module_locks[name] + _module_locks[name] = _weakref.ref(lock, cb) + return lock + +def _lock_unlock_module(name): + """Release the global import lock, and acquires then release the + module lock for a given module name. + This is used to ensure a module is completely initialized, in the + event it is being imported by another thread. + + Should only be called with the import lock taken.""" + lock = _get_module_lock(name) + _imp.release_lock() + try: + lock.acquire() + except _DeadlockError: + # Concurrent circular import, we'll accept a partially initialized + # module object. + pass + else: + lock.release() + + # Finder/loader utility code ################################################## _PYCACHE = '__pycache__' @@ -264,12 +403,15 @@ def module_for_loader(fxn): else: module.__package__ = fullname.rpartition('.')[0] try: + module.__initializing__ = True # If __package__ was not set above, __import__() will do it later. return fxn(self, module, *args, **kwargs) except: if not is_reload: del sys.modules[fullname] raise + finally: + module.__initializing__ = False _wrap(module_for_loader_wrapper, fxn) return module_for_loader_wrapper @@ -932,7 +1074,8 @@ def _find_module(name, path): if not sys.meta_path: _warnings.warn('sys.meta_path is empty', ImportWarning) for finder in sys.meta_path: - loader = finder.find_module(name, path) + with _ImportLockContext(): + loader = finder.find_module(name, path) if loader is not None: # The parent import may have already imported this module. if name not in sys.modules: @@ -962,8 +1105,7 @@ def _sanity_check(name, package, level): _ERR_MSG = 'No module named {!r}' -def _find_and_load(name, import_): - """Find and load the module.""" +def _find_and_load_unlocked(name, import_): path = None parent = name.rpartition('.')[0] if parent: @@ -1009,6 +1151,19 @@ def _find_and_load(name, import_): return module +def _find_and_load(name, import_): + """Find and load the module, and release the import lock.""" + try: + lock = _get_module_lock(name) + finally: + _imp.release_lock() + lock.acquire() + try: + return _find_and_load_unlocked(name, import_) + finally: + lock.release() + + def _gcd_import(name, package=None, level=0): """Import and return the module based on its name, the package the call is being made from, and the level adjustment. @@ -1021,17 +1176,17 @@ def _gcd_import(name, package=None, level=0): _sanity_check(name, package, level) if level > 0: name = _resolve_name(name, package, level) - with _ImportLockContext(): - try: - module = sys.modules[name] - if module is None: - message = ("import of {} halted; " - "None in sys.modules".format(name)) - raise ImportError(message, name=name) - return module - except KeyError: - pass # Don't want to chain the exception + _imp.acquire_lock() + if name not in sys.modules: return _find_and_load(name, _gcd_import) + module = sys.modules[name] + if module is None: + _imp.release_lock() + message = ("import of {} halted; " + "None in sys.modules".format(name)) + raise ImportError(message, name=name) + _lock_unlock_module(name) + return module def _handle_fromlist(module, fromlist, import_): @@ -1149,7 +1304,17 @@ def _setup(sys_module, _imp_module): continue else: raise ImportError('importlib requires posix or nt') + + try: + thread_module = BuiltinImporter.load_module('_thread') + except ImportError: + # Python was built without threads + thread_module = None + weakref_module = BuiltinImporter.load_module('_weakref') + setattr(self_module, '_os', os_module) + setattr(self_module, '_thread', thread_module) + setattr(self_module, '_weakref', weakref_module) setattr(self_module, 'path_sep', path_sep) setattr(self_module, 'path_separators', set(path_separators)) # Constants |