Edit File: mmap_dict.py
import json import mmap import os import struct _INITIAL_MMAP_SIZE = 1 << 20 _pack_integer_func = struct.Struct(b'i').pack _pack_double_func = struct.Struct(b'd').pack _unpack_integer = struct.Struct(b'i').unpack_from _unpack_double = struct.Struct(b'd').unpack_from # struct.pack_into has atomicity issues because it will temporarily write 0 into # the mmap, resulting in false reads to 0 when experiencing a lot of writes. # Using direct assignment solves this issue. def _pack_double(data, pos, value): data[pos:pos + 8] = _pack_double_func(value) def _pack_integer(data, pos, value): data[pos:pos + 4] = _pack_integer_func(value) def _read_all_values(data, used=0): """Yield (key, value, pos). No locking is performed.""" if used <= 0: # If not valid `used` value is passed in, read it from the file. used = _unpack_integer(data, 0)[0] pos = 8 while pos < used: encoded_len = _unpack_integer(data, pos)[0] # check we are not reading beyond bounds if encoded_len + pos > used: raise RuntimeError('Read beyond file size detected, file is corrupted.') pos += 4 encoded_key = data[pos : pos + encoded_len] padded_len = encoded_len + (8 - (encoded_len + 4) % 8) pos += padded_len value = _unpack_double(data, pos)[0] yield encoded_key.decode('utf-8'), value, pos pos += 8 class MmapedDict(object): """A dict of doubles, backed by an mmapped file. The file starts with a 4 byte int, indicating how much of it is used. Then 4 bytes of padding. There's then a number of entries, consisting of a 4 byte int which is the size of the next field, a utf-8 encoded string key, padding to a 8 byte alignment, and then a 8 byte float which is the value. Not thread safe. """ def __init__(self, filename, read_mode=False): self._f = open(filename, 'rb' if read_mode else 'a+b') self._fname = filename capacity = os.fstat(self._f.fileno()).st_size if capacity == 0: self._f.truncate(_INITIAL_MMAP_SIZE) capacity = _INITIAL_MMAP_SIZE self._capacity = capacity self._m = mmap.mmap(self._f.fileno(), self._capacity, access=mmap.ACCESS_READ if read_mode else mmap.ACCESS_WRITE) self._positions = {} self._used = _unpack_integer(self._m, 0)[0] if self._used == 0: self._used = 8 _pack_integer(self._m, 0, self._used) else: if not read_mode: for key, _, pos in self._read_all_values(): self._positions[key] = pos @staticmethod def read_all_values_from_file(filename): with open(filename, 'rb') as infp: # Read the first block of data, including the first 4 bytes which tell us # how much of the file (which is preallocated to _INITIAL_MMAP_SIZE bytes) is occupied. data = infp.read(mmap.PAGESIZE) used = _unpack_integer(data, 0)[0] if used > len(data): # Then read in the rest, if needed. data += infp.read(used - len(data)) return _read_all_values(data, used) def _init_value(self, key): """Initialize a value. Lock must be held by caller.""" encoded = key.encode('utf-8') # Pad to be 8-byte aligned. padded = encoded + (b' ' * (8 - (len(encoded) + 4) % 8)) value = struct.pack('i{0}sd'.format(len(padded)).encode(), len(encoded), padded, 0.0) while self._used + len(value) > self._capacity: self._capacity *= 2 self._f.truncate(self._capacity) self._m = mmap.mmap(self._f.fileno(), self._capacity) self._m[self._used:self._used + len(value)] = value # Update how much space we've used. self._used += len(value) _pack_integer(self._m, 0, self._used) self._positions[key] = self._used - 8 def _read_all_values(self): """Yield (key, value, pos). No locking is performed.""" return _read_all_values(data=self._m, used=self._used) def read_all_values(self): """Yield (key, value). No locking is performed.""" for k, v, _ in self._read_all_values(): yield k, v def read_value(self, key): if key not in self._positions: self._init_value(key) pos = self._positions[key] # We assume that reading from an 8 byte aligned value is atomic return _unpack_double(self._m, pos)[0] def write_value(self, key, value): if key not in self._positions: self._init_value(key) pos = self._positions[key] # We assume that writing to an 8 byte aligned value is atomic _pack_double(self._m, pos, value) def close(self): if self._f: self._m.close() self._m = None self._f.close() self._f = None def mmap_key(metric_name, name, labelnames, labelvalues): """Format a key for use in the mmap file.""" # ensure labels are in consistent order for identity labels = dict(zip(labelnames, labelvalues)) return json.dumps([metric_name, name, labels], sort_keys=True)