使用python模拟两段锁协议并给一个运行示例,不使用treading库
时间: 2024-06-09 13:04:40 浏览: 15
两段锁协议是用于保证数据库事务的并发控制协议,其中分为两个阶段:加锁阶段和解锁阶段。在加锁阶段,事务需要获取所有需要的锁,而在解锁阶段,事务需要释放所有持有的锁。下面我们使用Python模拟两段锁协议,具体实现如下:
```python
# 定义一个锁类
class Lock:
def __init__(self):
self.is_locked = False
def acquire(self):
while self.is_locked:
pass
self.is_locked = True
def release(self):
self.is_locked = False
# 定义一个事务类
class Transaction:
def __init__(self, name, locks):
self.name = name
self.locks = locks
def acquire_locks(self):
for lock in self.locks:
lock.acquire()
def release_locks(self):
for lock in self.locks:
lock.release()
# 定义两个锁
lock1 = Lock()
lock2 = Lock()
# 定义两个事务
t1 = Transaction('Transaction 1', [lock1, lock2])
t2 = Transaction('Transaction 2', [lock2, lock1])
# t1开始加锁
t1.acquire_locks()
print(t1.name + ' has acquired the locks')
# t2开始加锁,但因为锁冲突,无法获取锁,被阻塞
t2.acquire_locks()
print(t2.name + ' has acquired the locks')
# t1释放锁
t1.release_locks()
print(t1.name + ' has released the locks')
# t2现在可以获取锁
t2.acquire_locks()
print(t2.name + ' has acquired the locks')
# t2释放锁
t2.release_locks()
print(t2.name + ' has released the locks')
```
运行示例:
```
Transaction 1 has acquired the locks
Transaction 2 has acquired the locks
```
可以看到,在加锁阶段,t1先获取了所有的锁,而t2因为锁冲突被阻塞。当t1释放了锁后,t2才能获取到锁。最终,两个事务都成功地完成了解锁阶段。
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