锁
python的内置数据结构比如列表和字典等是线程安全的，但是简单数据类型比如整数和浮点数则不是线程安全的，要这些简单数据类型的通过操作，就需要使用锁。
#!/usr/bin/env python3# coding=utf-8import threadingshared_resource_with_lock = 0shared_resource_with_no_lock = 0count = 100000shared_resource_lock = threading.lock()####lock management##def increment_with_lock(): global shared_resource_with_lock for i in range(count): shared_resource_lock.acquire() shared_resource_with_lock += 1 shared_resource_lock.release() def decrement_with_lock(): global shared_resource_with_lock for i in range(count): shared_resource_lock.acquire() shared_resource_with_lock -= 1 shared_resource_lock.release() ####no lock management ## def increment_without_lock(): global shared_resource_with_no_lock for i in range(count): shared_resource_with_no_lock += 1 def decrement_without_lock(): global shared_resource_with_no_lock for i in range(count): shared_resource_with_no_lock -= 1 ####the main programif __name__ == __main__: t1 = threading.thread(target = increment_with_lock) t2 = threading.thread(target = decrement_with_lock) t3 = threading.thread(target = increment_without_lock) t4 = threading.thread(target = decrement_without_lock) t1.start() t2.start() t3.start() t4.start() t1.join() t2.join() t3.join() t4.join() print (the value of shared variable with lock management is %s\ %shared_resource_with_lock) print (the value of shared variable with race condition is %s\ %shared_resource_with_no_lock)
执行结果：
$ ./threading_lock.py
the value of shared variable with lock management is 0the value of shared variable with race condition is 0
又如：
import randomimport threadingimport timelogging.basicconfig(level=logging.debug, format='(%(threadname)-10s) %(message)s', ) class counter(object): def __init__(self, start=0): self.lock = threading.lock() self.value = start def increment(self): logging.debug(time.ctime(time.time())) logging.debug('waiting for lock') self.lock.acquire() try: pause = random.randint(1,3) logging.debug(time.ctime(time.time())) logging.debug('acquired lock') self.value = self.value + 1 logging.debug('lock {0} seconds'.format(pause)) time.sleep(pause) finally: self.lock.release()def worker(c): for i in range(2): pause = random.randint(1,3) logging.debug(time.ctime(time.time())) logging.debug('sleeping %0.02f', pause) time.sleep(pause) c.increment() logging.debug('done')counter = counter()for i in range(2): t = threading.thread(target=worker, args=(counter,)) t.start()logging.debug('waiting for worker threads')main_thread = threading.currentthread()for t in threading.enumerate(): if t is not main_thread: t.join()logging.debug('counter: %d', counter.value)
执行结果：
$ python threading_lock.py
(thread-1 ) tue sep 15 15:49:18 2015(thread-1 ) sleeping 3.00(thread-2 ) tue sep 15 15:49:18 2015(mainthread) waiting for worker threads(thread-2 ) sleeping 2.00(thread-2 ) tue sep 15 15:49:20 2015(thread-2 ) waiting for lock(thread-2 ) tue sep 15 15:49:20 2015(thread-2 ) acquired lock(thread-2 ) lock 2 seconds(thread-1 ) tue sep 15 15:49:21 2015(thread-1 ) waiting for lock(thread-2 ) tue sep 15 15:49:22 2015(thread-1 ) tue sep 15 15:49:22 2015(thread-2 ) sleeping 2.00(thread-1 ) acquired lock(thread-1 ) lock 1 seconds(thread-1 ) tue sep 15 15:49:23 2015(thread-1 ) sleeping 2.00(thread-2 ) tue sep 15 15:49:24 2015(thread-2 ) waiting for lock(thread-2 ) tue sep 15 15:49:24 2015(thread-2 ) acquired lock(thread-2 ) lock 1 seconds(thread-1 ) tue sep 15 15:49:25 2015(thread-1 ) waiting for lock(thread-1 ) tue sep 15 15:49:25 2015(thread-1 ) acquired lock(thread-1 ) lock 2 seconds(thread-2 ) done(thread-1 ) done(mainthread) counter: 4
acquire()中传入false值，可以检查是否获得了锁。比如：
import loggingimport threadingimport timelogging.basicconfig(level=logging.debug, format='(%(threadname)-10s) %(message)s', ) def lock_holder(lock): logging.debug('starting') while true: lock.acquire() try: logging.debug('holding') time.sleep(0.5) finally: logging.debug('not holding') lock.release() time.sleep(0.5) return def worker(lock): logging.debug('starting') num_tries = 0 num_acquires = 0 while num_acquires 0: print (adding 1 item in the box\n) box.add() time.sleep(5) items -= 1 def remover(box,items): while items > 0: print (removing 1 item in the box) box.remove() time.sleep(5) items -= 1 ## the main program build some## threads and make sure it worksif __name__ == __main__: items = 5 print (putting %s items in the box % items) box = box() t1 = threading.thread(target=adder,args=(box,items)) t2 = threading.thread(target=remover,args=(box,items)) t1.start() t2.start() t1.join() t2.join() print (%s items still remain in the box % box.total_items)
执行结果：
$ python3 threading_rlock2.py
putting 5 items in the box adding 1 item in the boxremoving 1 item in the boxadding 1 item in the boxremoving 1 item in the boxadding 1 item in the boxremoving 1 item in the boxremoving 1 item in the boxadding 1 item in the boxremoving 1 item in the boxadding 1 item in the box0 items still remain in the box