| 4 | ################################################################################ |
| 5 | |
| 6 | class DAL2: |
| 7 | |
| 8 | # CONSTANTS |
| 9 | MAX_BLOCKS = (2 ** 16) - 1 |
| 10 | MAX_SIZE = (2 ** 16) |
| 11 | |
| 12 | # Disk Abstraction Layer |
| 13 | def __init__(self, blocks, size): |
| 14 | assert type(blocks) is int and 1 <= blocks <= self.MAX_BLOCKS |
| 15 | assert type(size) is int and 1 <= size <= self.MAX_SIZE |
| 16 | blocks = int(ceil(float(blocks * (size + 1)) / size)) |
| 17 | assert blocks <= self.MAX_SIZE |
| 18 | DAL1.BLOCKS = blocks |
| 19 | DAL1.SIZE = size |
| 20 | self.__disk = DAL1() |
| 21 | self.__blocks = (blocks * size) / (size + 1) |
| 22 | self.__index = (blocks - self.__blocks) * size |
| 23 | self.__BIT = [0 for index in range(self.__blocks)] |
| 24 | |
| 25 | # Open A Block |
| 26 | def open(self, status): |
| 27 | assert type(status) is int and 1 <= status <= 255 |
| 28 | index = self.__BIT.index(0) |
| 29 | self.__BIT[index] = status |
| 30 | return index |
| 31 | |
| 32 | # Read A Block |
| 33 | def read(self, block): |
| 34 | assert type(block) is int and 0 <= block < self.__blocks |
| 35 | assert self.__BIT[block] != 0 |
| 36 | return self.__disk.read(self.__index + block * self.__disk.SIZE, \ |
| 37 | self.__disk.SIZE) |
| 38 | |
| 39 | # Write A Block |
| 40 | def write(self, block, data): |
| 41 | assert type(block) is int and 0 <= block < self.__blocks |
| 42 | assert type(data) is str and len(data) == self.__disk.SIZE |
| 43 | assert self.__BIT[block] != 0 |
| 44 | self.__disk.write(self.__index + block * self.__disk.SIZE, data) |
| 45 | |
| 46 | # Close A Block |
| 47 | def close(self, block): |
| 48 | assert type(block) is int and 0 <= block < self.__blocks |
| 49 | assert self.__BIT[block] != 0 |
| 50 | self.__disk.erase(self.__index + block * self.__disk.SIZE, \ |
| 51 | self.__disk.SIZE) |
| 52 | self.__BIT[block] = 0 |
| 53 | |
| 54 | # Get Status Information |
| 55 | def status(self, block): |
| 56 | assert type(block) is int and 0 <= block < self.__blocks |
| 57 | return self.__BIT[block] |
| 58 | |
| 59 | # Probability Of Failure |
| 60 | def fail(self, probability): |
| 61 | self.__disk.fail(probability) |
| 62 | |
| 63 | # Dump To File |