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mman.py
"""Module containing a memory memory manager which provides a sliding window on a number of memory mapped files""" from .util import ( MapWindow, MapRegion, MapRegionList, is_64_bit, ) import sys from functools import reduce __all__ = ["StaticWindowMapManager", "SlidingWindowMapManager", "WindowCursor"] #{ Utilities #}END utilities class WindowCursor: """ Pointer into the mapped region of the memory manager, keeping the map alive until it is destroyed and no other client uses it. Cursors should not be created manually, but are instead returned by the SlidingWindowMapManager **Note:**: The current implementation is suited for static and sliding window managers, but it also means that it must be suited for the somewhat quite different sliding manager. It could be improved, but I see no real need to do so.""" __slots__ = ( '_manager', # the manger keeping all file regions '_rlist', # a regions list with regions for our file '_region', # our current class:`MapRegion` or None '_ofs', # relative offset from the actually mapped area to our start area '_size' # maximum size we should provide ) def __init__(self, manager=None, regions=None): self._manager = manager self._rlist = regions self._region = None self._ofs = 0 self._size = 0 def __del__(self): self._destroy() def __enter__(self): return self def __exit__(self, exc_type, exc_value, traceback): self._destroy() def _destroy(self): """Destruction code to decrement counters""" self.unuse_region() if self._rlist is not None: # Actual client count, which doesn't include the reference kept by the manager, nor ours # as we are about to be deleted try: if len(self._rlist) == 0: # Free all resources associated with the mapped file self._manager._fdict.pop(self._rlist.path_or_fd()) # END remove regions list from manager except (TypeError, KeyError): # sometimes, during shutdown, getrefcount is None. Its possible # to re-import it, however, its probably better to just ignore # this python problem (for now). # The next step is to get rid of the error prone getrefcount alltogether. pass # END exception handling # END handle regions def _copy_from(self, rhs): """Copy all data from rhs into this instance, handles usage count""" self._manager = rhs._manager self._rlist = type(rhs._rlist)(rhs._rlist) self._region = rhs._region self._ofs = rhs._ofs self._size = rhs._size for region in self._rlist: region.increment_client_count() if self._region is not None: self._region.increment_client_count() # END handle regions def __copy__(self): """copy module interface""" cpy = type(self)() cpy._copy_from(self) return cpy #{ Interface def assign(self, rhs): """Assign rhs to this instance. This is required in order to get a real copy. Alternativly, you can copy an existing instance using the copy module""" self._destroy() self._copy_from(rhs) def use_region(self, offset=0, size=0, flags=0): """Assure we point to a window which allows access to the given offset into the file :param offset: absolute offset in bytes into the file :param size: amount of bytes to map. If 0, all available bytes will be mapped :param flags: additional flags to be given to os.open in case a file handle is initially opened for mapping. Has no effect if a region can actually be reused. :return: this instance - it should be queried for whether it points to a valid memory region. This is not the case if the mapping failed because we reached the end of the file **Note:**: The size actually mapped may be smaller than the given size. If that is the case, either the file has reached its end, or the map was created between two existing regions""" need_region = True man = self._manager fsize = self._rlist.file_size() size = min(size or fsize, man.window_size() or fsize) # clamp size to window size if self._region is not None: if self._region.includes_ofs(offset): need_region = False else: self.unuse_region() # END handle existing region # END check existing region # offset too large ? if offset >= fsize: return self # END handle offset if need_region: self._region = man._obtain_region(self._rlist, offset, size, flags, False) self._region.increment_client_count() # END need region handling self._ofs = offset - self._region._b self._size = min(size, self._region.ofs_end() - offset) return self def unuse_region(self): """Unuse the current region. Does nothing if we have no current region **Note:** the cursor unuses the region automatically upon destruction. It is recommended to un-use the region once you are done reading from it in persistent cursors as it helps to free up resource more quickly""" if self._region is not None: self._region.increment_client_count(-1) self._region = None # note: should reset ofs and size, but we spare that for performance. Its not # allowed to query information if we are not valid ! def buffer(self): """Return a buffer object which allows access to our memory region from our offset to the window size. Please note that it might be smaller than you requested when calling use_region() **Note:** You can only obtain a buffer if this instance is_valid() ! **Note:** buffers should not be cached passed the duration of your access as it will prevent resources from being freed even though they might not be accounted for anymore !""" return memoryview(self._region.buffer())[self._ofs:self._ofs+self._size] def map(self): """ :return: the underlying raw memory map. Please not that the offset and size is likely to be different to what you set as offset and size. Use it only if you are sure about the region it maps, which is the whole file in case of StaticWindowMapManager""" return self._region.map() def is_valid(self): """:return: True if we have a valid and usable region""" return self._region is not None def is_associated(self): """:return: True if we are associated with a specific file already""" return self._rlist is not None def ofs_begin(self): """:return: offset to the first byte pointed to by our cursor **Note:** only if is_valid() is True""" return self._region._b + self._ofs def ofs_end(self): """:return: offset to one past the last available byte""" # unroll method calls for performance ! return self._region._b + self._ofs + self._size def size(self): """:return: amount of bytes we point to""" return self._size def region(self): """:return: our mapped region, or None if nothing is mapped yet :raise AssertionError: if we have no current region. This is only useful for debugging""" return self._region def includes_ofs(self, ofs): """:return: True if the given absolute offset is contained in the cursors current region **Note:** cursor must be valid for this to work""" # unroll methods return (self._region._b + self._ofs) <= ofs < (self._region._b + self._ofs + self._size) def file_size(self): """:return: size of the underlying file""" return self._rlist.file_size() def path_or_fd(self): """:return: path or file descriptor of the underlying mapped file""" return self._rlist.path_or_fd() def path(self): """:return: path of the underlying mapped file :raise ValueError: if attached path is not a path""" if isinstance(self._rlist.path_or_fd(), int): raise ValueError("Path queried although mapping was applied to a file descriptor") # END handle type return self._rlist.path_or_fd() def fd(self): """:return: file descriptor used to create the underlying mapping. **Note:** it is not required to be valid anymore :raise ValueError: if the mapping was not created by a file descriptor""" if isinstance(self._rlist.path_or_fd(), str): raise ValueError("File descriptor queried although mapping was generated from path") # END handle type return self._rlist.path_or_fd() #} END interface class StaticWindowMapManager: """Provides a manager which will produce single size cursors that are allowed to always map the whole file. Clients must be written to specifically know that they are accessing their data through a StaticWindowMapManager, as they otherwise have to deal with their window size. These clients would have to use a SlidingWindowMapBuffer to hide this fact. This type will always use a maximum window size, and optimize certain methods to accommodate this fact""" __slots__ = [ '_fdict', # mapping of path -> StorageHelper (of some kind '_window_size', # maximum size of a window '_max_memory_size', # maximum amount of memory we may allocate '_max_handle_count', # maximum amount of handles to keep open '_memory_size', # currently allocated memory size '_handle_count', # amount of currently allocated file handles ] #{ Configuration MapRegionListCls = MapRegionList MapWindowCls = MapWindow MapRegionCls = MapRegion WindowCursorCls = WindowCursor #} END configuration _MB_in_bytes = 1024 * 1024 def __init__(self, window_size=0, max_memory_size=0, max_open_handles=sys.maxsize): """initialize the manager with the given parameters. :param window_size: if -1, a default window size will be chosen depending on the operating system's architecture. It will internally be quantified to a multiple of the page size If 0, the window may have any size, which basically results in mapping the whole file at one :param max_memory_size: maximum amount of memory we may map at once before releasing mapped regions. If 0, a viable default will be set depending on the system's architecture. It is a soft limit that is tried to be kept, but nothing bad happens if we have to over-allocate :param max_open_handles: if not maxint, limit the amount of open file handles to the given number. Otherwise the amount is only limited by the system itself. If a system or soft limit is hit, the manager will free as many handles as possible""" self._fdict = dict() self._window_size = window_size self._max_memory_size = max_memory_size self._max_handle_count = max_open_handles self._memory_size = 0 self._handle_count = 0 if window_size < 0: coeff = 64 if is_64_bit(): coeff = 1024 # END handle arch self._window_size = coeff * self._MB_in_bytes # END handle max window size if max_memory_size == 0: coeff = 1024 if is_64_bit(): coeff = 8192 # END handle arch self._max_memory_size = coeff * self._MB_in_bytes # END handle max memory size #{ Internal Methods def _collect_lru_region(self, size): """Unmap the region which was least-recently used and has no client :param size: size of the region we want to map next (assuming its not already mapped partially or full if 0, we try to free any available region :return: Amount of freed regions .. Note:: We don't raise exceptions anymore, in order to keep the system working, allowing temporary overallocation. If the system runs out of memory, it will tell. .. TODO:: implement a case where all unusued regions are discarded efficiently. Currently its only brute force """ num_found = 0 while (size == 0) or (self._memory_size + size > self._max_memory_size): lru_region = None lru_list = None for regions in self._fdict.values(): for region in regions: # check client count - if it's 1, it's just us if (region.client_count() == 1 and (lru_region is None or region._uc < lru_region._uc)): lru_region = region lru_list = regions # END update lru_region # END for each region # END for each regions list if lru_region is None: break # END handle region not found num_found += 1 del(lru_list[lru_list.index(lru_region)]) lru_region.increment_client_count(-1) self._memory_size -= lru_region.size() self._handle_count -= 1 # END while there is more memory to free return num_found def _obtain_region(self, a, offset, size, flags, is_recursive): """Utilty to create a new region - for more information on the parameters, see MapCursor.use_region. :param a: A regions (a)rray :return: The newly created region""" if self._memory_size + size > self._max_memory_size: self._collect_lru_region(size) # END handle collection r = None if a: assert len(a) == 1 r = a[0] else: try: r = self.MapRegionCls(a.path_or_fd(), 0, sys.maxsize, flags) except Exception: # apparently we are out of system resources or hit a limit # As many more operations are likely to fail in that condition ( # like reading a file from disk, etc) we free up as much as possible # As this invalidates our insert position, we have to recurse here if is_recursive: # we already tried this, and still have no success in obtaining # a mapping. This is an exception, so we propagate it raise # END handle existing recursion self._collect_lru_region(0) return self._obtain_region(a, offset, size, flags, True) # END handle exceptions self._handle_count += 1 self._memory_size += r.size() a.append(r) # END handle array assert r.includes_ofs(offset) return r #}END internal methods #{ Interface def make_cursor(self, path_or_fd): """ :return: a cursor pointing to the given path or file descriptor. It can be used to map new regions of the file into memory **Note:** if a file descriptor is given, it is assumed to be open and valid, but may be closed afterwards. To refer to the same file, you may reuse your existing file descriptor, but keep in mind that new windows can only be mapped as long as it stays valid. This is why the using actual file paths are preferred unless you plan to keep the file descriptor open. **Note:** file descriptors are problematic as they are not necessarily unique, as two different files opened and closed in succession might have the same file descriptor id. **Note:** Using file descriptors directly is faster once new windows are mapped as it prevents the file to be opened again just for the purpose of mapping it.""" regions = self._fdict.get(path_or_fd) if regions is None: regions = self.MapRegionListCls(path_or_fd) self._fdict[path_or_fd] = regions # END obtain region for path return self.WindowCursorCls(self, regions) def collect(self): """Collect all available free-to-collect mapped regions :return: Amount of freed handles""" return self._collect_lru_region(0) def num_file_handles(self): """:return: amount of file handles in use. Each mapped region uses one file handle""" return self._handle_count def num_open_files(self): """Amount of opened files in the system""" return reduce(lambda x, y: x + y, (1 for rlist in self._fdict.values() if len(rlist) > 0), 0) def window_size(self): """:return: size of each window when allocating new regions""" return self._window_size def mapped_memory_size(self): """:return: amount of bytes currently mapped in total""" return self._memory_size def max_file_handles(self): """:return: maximium amount of handles we may have opened""" return self._max_handle_count def max_mapped_memory_size(self): """:return: maximum amount of memory we may allocate""" return self._max_memory_size #} END interface #{ Special Purpose Interface def force_map_handle_removal_win(self, base_path): """ONLY AVAILABLE ON WINDOWS On windows removing files is not allowed if anybody still has it opened. If this process is ourselves, and if the whole process uses this memory manager (as far as the parent framework is concerned) we can enforce closing all memory maps whose path matches the given base path to allow the respective operation after all. The respective system must NOT access the closed memory regions anymore ! This really may only be used if you know that the items which keep the cursors alive will not be using it anymore. They need to be recreated ! :return: Amount of closed handles **Note:** does nothing on non-windows platforms""" if sys.platform != 'win32': return # END early bailout num_closed = 0 for path, rlist in self._fdict.items(): if path.startswith(base_path): for region in rlist: region.release() num_closed += 1 # END path matches # END for each path return num_closed #} END special purpose interface class SlidingWindowMapManager(StaticWindowMapManager): """Maintains a list of ranges of mapped memory regions in one or more files and allows to easily obtain additional regions assuring there is no overlap. Once a certain memory limit is reached globally, or if there cannot be more open file handles which result from each mmap call, the least recently used, and currently unused mapped regions are unloaded automatically. **Note:** currently not thread-safe ! **Note:** in the current implementation, we will automatically unload windows if we either cannot create more memory maps (as the open file handles limit is hit) or if we have allocated more than a safe amount of memory already, which would possibly cause memory allocations to fail as our address space is full.""" __slots__ = tuple() def __init__(self, window_size=-1, max_memory_size=0, max_open_handles=sys.maxsize): """Adjusts the default window size to -1""" super().__init__(window_size, max_memory_size, max_open_handles) def _obtain_region(self, a, offset, size, flags, is_recursive): # bisect to find an existing region. The c++ implementation cannot # do that as it uses a linked list for regions. r = None lo = 0 hi = len(a) while lo < hi: mid = (lo + hi) // 2 ofs = a[mid]._b if ofs <= offset: if a[mid].includes_ofs(offset): r = a[mid] break # END have region lo = mid + 1 else: hi = mid # END handle position # END while bisecting if r is None: window_size = self._window_size left = self.MapWindowCls(0, 0) mid = self.MapWindowCls(offset, size) right = self.MapWindowCls(a.file_size(), 0) # we want to honor the max memory size, and assure we have anough # memory available # Save calls ! if self._memory_size + window_size > self._max_memory_size: self._collect_lru_region(window_size) # END handle collection # we assume the list remains sorted by offset insert_pos = 0 len_regions = len(a) if len_regions == 1: if a[0]._b <= offset: insert_pos = 1 # END maintain sort else: # find insert position insert_pos = len_regions for i, region in enumerate(a): if region._b > offset: insert_pos = i break # END if insert position is correct # END for each region # END obtain insert pos # adjust the actual offset and size values to create the largest # possible mapping if insert_pos == 0: if len_regions: right = self.MapWindowCls.from_region(a[insert_pos]) # END adjust right side else: if insert_pos != len_regions: right = self.MapWindowCls.from_region(a[insert_pos]) # END adjust right window left = self.MapWindowCls.from_region(a[insert_pos - 1]) # END adjust surrounding windows mid.extend_left_to(left, window_size) mid.extend_right_to(right, window_size) mid.align() # it can happen that we align beyond the end of the file if mid.ofs_end() > right.ofs: mid.size = right.ofs - mid.ofs # END readjust size # insert new region at the right offset to keep the order try: if self._handle_count >= self._max_handle_count: raise Exception # END assert own imposed max file handles r = self.MapRegionCls(a.path_or_fd(), mid.ofs, mid.size, flags) except Exception: # apparently we are out of system resources or hit a limit # As many more operations are likely to fail in that condition ( # like reading a file from disk, etc) we free up as much as possible # As this invalidates our insert position, we have to recurse here if is_recursive: # we already tried this, and still have no success in obtaining # a mapping. This is an exception, so we propagate it raise # END handle existing recursion self._collect_lru_region(0) return self._obtain_region(a, offset, size, flags, True) # END handle exceptions self._handle_count += 1 self._memory_size += r.size() a.insert(insert_pos, r) # END create new region return r
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