举例讲解Python编程中对线程锁的使用

2024-03-15 17:20:03 505

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/envpython3
#coding=utf-8

importthreading

shared_resource_with_lock=0
shared_resource_with_no_lock=0
COUNT=100000
shared_resource_lock=threading.Lock()

####LOCKMANAGEMENT##
defincrement_with_lock():
globalshared_resource_with_lock
foriinrange(COUNT):
shared_resource_lock.acquire()
shared_resource_with_lock+=1
shared_resource_lock.release()

defdecrement_with_lock():
globalshared_resource_with_lock
foriinrange(COUNT):
shared_resource_lock.acquire()
shared_resource_with_lock-=1
shared_resource_lock.release()
####NOLOCKMANAGEMENT##

defincrement_without_lock():
globalshared_resource_with_no_lock
foriinrange(COUNT):
shared_resource_with_no_lock+=1

defdecrement_without_lock():
globalshared_resource_with_no_lock
foriinrange(COUNT):
shared_resource_with_no_lock-=1

####theMainprogram
if__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("thevalueofsharedvariablewithlockmanagementis%s"\
%shared_resource_with_lock)
print("thevalueofsharedvariablewithraceconditionis%s"\
%shared_resource_with_no_lock)

执行结果：

$./threading_lock.py

thevalueofsharedvariablewithlockmanagementis0
thevalueofsharedvariablewithraceconditionis0

又如：

importrandom
importthreading
importtime
logging.basicConfig(level=logging.DEBUG,
format='(%(threadName)-10s)%(message)s',
)

classCounter(object):
def__init__(self,start=0):
self.lock=threading.Lock()
self.value=start
defincrement(self):
logging.debug(time.ctime(time.time()))
logging.debug('Waitingforlock')
self.lock.acquire()
try:
pause=random.randint(1,3)
logging.debug(time.ctime(time.time()))
logging.debug('Acquiredlock')
self.value=self.value+1
logging.debug('lock{0}seconds'.format(pause))
time.sleep(pause)
finally:
self.lock.release()
defworker(c):
foriinrange(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()
foriinrange(2):
t=threading.Thread(target=worker,args=(counter,))
t.start()
logging.debug('Waitingforworkerthreads')
main_thread=threading.currentThread()
fortinthreading.enumerate():
iftisnotmain_thread:
t.join()
logging.debug('Counter:%d',counter.value)

执行结果：

$pythonthreading_lock.py

(Thread-1)TueSep1515:49:182015
(Thread-1)Sleeping3.00
(Thread-2)TueSep1515:49:182015
(MainThread)Waitingforworkerthreads
(Thread-2)Sleeping2.00
(Thread-2)TueSep1515:49:202015
(Thread-2)Waitingforlock
(Thread-2)TueSep1515:49:202015
(Thread-2)Acquiredlock
(Thread-2)lock2seconds
(Thread-1)TueSep1515:49:212015
(Thread-1)Waitingforlock
(Thread-2)TueSep1515:49:222015
(Thread-1)TueSep1515:49:222015
(Thread-2)Sleeping2.00
(Thread-1)Acquiredlock
(Thread-1)lock1seconds
(Thread-1)TueSep1515:49:232015
(Thread-1)Sleeping2.00
(Thread-2)TueSep1515:49:242015
(Thread-2)Waitingforlock
(Thread-2)TueSep1515:49:242015
(Thread-2)Acquiredlock
(Thread-2)lock1seconds
(Thread-1)TueSep1515:49:252015
(Thread-1)Waitingforlock
(Thread-1)TueSep1515:49:252015
(Thread-1)Acquiredlock
(Thread-1)lock2seconds
(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：

importlogging
importthreading
importtime
logging.basicConfig(level=logging.DEBUG,
format='(%(threadName)-10s)%(message)s',
)

deflock_holder(lock):
logging.debug('Starting')
whileTrue:
lock.acquire()
try:
logging.debug('Holding')
time.sleep(0.5)
finally:
logging.debug('Notholding')
lock.release()
time.sleep(0.5)
return

defworker(lock):
logging.debug('Starting')
num_tries=0
num_acquires=0
whilenum_acquires<3:
time.sleep(0.5)
logging.debug('Tryingtoacquire')
have_it=lock.acquire(0)
try:
num_tries+=1
ifhave_it:
logging.debug('Iteration%d:Acquired',
num_tries)
num_acquires+=1
else:
logging.debug('Iteration%d:Notacquired',
num_tries)
finally:
ifhave_it:
lock.release()
logging.debug('Doneafter%diterations',num_tries)
lock=threading.Lock()
holder=threading.Thread(target=lock_holder,
args=(lock,),
name='LockHolder')
holder.setDaemon(True)
holder.start()
worker=threading.Thread(target=worker,
args=(lock,),
name='Worker')
worker.start()

执行结果：

$pythonthreading_lock_noblock.py

(LockHolder)Starting
(LockHolder)Holding
(Worker)Starting
(LockHolder)Notholding
(Worker)Tryingtoacquire
(Worker)Iteration1:Acquired
(LockHolder)Holding
(Worker)Tryingtoacquire
(Worker)Iteration2:Notacquired
(LockHolder)Notholding
(Worker)Tryingtoacquire
(Worker)Iteration3:Acquired
(LockHolder)Holding
(Worker)Tryingtoacquire
(Worker)Iteration4:Notacquired
(LockHolder)Notholding
(Worker)Tryingtoacquire
(Worker)Iteration5:Acquired
(Worker)Doneafter5iterations

线程安全锁

threading.RLock()

返回可重入锁对象。重入锁必须由获得它的线程释放。一旦线程获得了重入锁，同一线程可不阻塞地再次获得，获取之后必须释放。

通常一个线程只能获取一次锁：

importthreading

lock=threading.Lock()

print'Firsttry:',lock.acquire()
print'Secondtry:',lock.acquire(0)

执行结果：

$pythonthreading_lock_reacquire.py

Firsttry:True
Secondtry:False

使用RLock可以获取多次锁：

importthreading
lock=threading.RLock()
print'Firsttry:',lock.acquire()
print'Secondtry:',lock.acquire(0)

执行结果：

pythonthreading_rlock.py

Firsttry:True
Secondtry:1

再来看一个例子：

#!/usr/bin/envpython3
#coding=utf-8
importthreading
importtime
classBox(object):
lock=threading.RLock()
def__init__(self):
self.total_items=0
defexecute(self,n):
Box.lock.acquire()
self.total_items+=n
Box.lock.release()
defadd(self):
Box.lock.acquire()
self.execute(1)
Box.lock.release()
defremove(self):
Box.lock.acquire()
self.execute(-1)
Box.lock.release()

##Thesetwofunctionsrunninseparate
##threadsandcalltheBox'smethods
defadder(box,items):
whileitems>0:
print("adding1iteminthebox\n")
box.add()
time.sleep(5)
items-=1

defremover(box,items):
whileitems>0:
print("removing1iteminthebox")
box.remove()
time.sleep(5)
items-=1

##themainprogrambuildsome
##threadsandmakesureitworks
if__name__=="__main__":
items=5
print("putting%sitemsinthebox"%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("%sitemsstillremaininthebox"%box.total_items)

执行结果：

$python3threading_rlock2.py

putting5itemsinthebox
adding1iteminthebox
removing1iteminthebox
adding1iteminthebox
removing1iteminthebox
adding1iteminthebox
removing1iteminthebox
removing1iteminthebox
adding1iteminthebox
removing1iteminthebox
adding1iteminthebox
0itemsstillremaininthebox

举例讲解Python编程中对线程锁的使用

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