Python多线程死锁原理与基于锁排序的解决方案

class Sample:
  def __enter__(self):
    print('enter resources')
    return self
  
  def __exit__(self, exc_type, exc_val, exc_tb):
    print('exit')
    # print(exc_type)
    # print(exc_val)
    # print(exc_tb)

  def doSomething(self):
    a = 1/1
    return a

def getSample():
  return Sample()

if __name__ == '__main__':
  with getSample() as sample:
    print('do something')
    sample.doSomething()

import time
from contextlib import contextmanager

@contextmanager
def timethis(label):
  start = time.time()
  try:
    yield
  finally:
    end = time.time()
    print('{}: {}'.format(label, end - start))
    
    
with timethis('timer'):
  pass

from contextlib import contextmanager

# 用来存储local的数据
_local = threading.local()

@contextmanager
def acquire(*locks):
 # 对锁按照id进行排序
  locks = sorted(locks, key=lambda x: id(x))

  # 如果已经持有锁当中的序号有比当前更大的，说明策略失败
  acquired = getattr(_local,'acquired',[])
  if acquired and max(id(lock) for lock in acquired) >= id(locks[0]):
    raise RuntimeError('Lock Order Violation')

  # 获取所有锁
  acquired.extend(locks)
  _local.acquired = acquired

  try:
    for lock in locks:
      lock.acquire()
    yield
  finally:
    # 倒叙释放
    for lock in reversed(locks):
      lock.release()
    del acquired[-len(locks):]

x_lock = threading.Lock()
y_lock = threading.Lock()

def thread_1():
  while True:
    with acquire(x_lock, y_lock):
      print('Thread-1')

def thread_2():
  while True:
    with acquire(y_lock, x_lock):
      print('Thread-2')

t1 = threading.Thread(target=thread_1)
t1.start()

t2 = threading.Thread(target=thread_2)
t2.start()

def thread_1():
  while True:
    with acquire(x_lock):
      with acquire(y_lock):
       print('Thread-1')

def thread_2():
  while True:
    with acquire(y_lock):
      with acquire(x_lock):
       print('Thread-1')

import threading

def philosopher(left, right):
  while True:
    with acquire(left,right):
       print(threading.currentThread(), 'eating')

# 叉子的数量
NSTICKS = 5
chopsticks = [threading.Lock() for n in range(NSTICKS)]

for n in range(NSTICKS):
  t = threading.Thread(target=philosopher,
             args=(chopsticks[n],chopsticks[(n+1) % NSTICKS]))
  t.start()