📅  最后修改于: 2020-12-23 05:04:37             🧑  作者: Mango
运行多个线程类似于同时运行多个不同的程序,但具有以下优点-
进程中的多个线程与主线程共享相同的数据空间,因此与单独的进程相比,可以更轻松地共享信息或彼此通信。
线程有时被称为轻量级进程,它们不需要太多的内存开销。它们比流程便宜。
线程具有开始,执行序列和结论。它具有一个指令指针,可跟踪其上下文中当前正在运行的位置。
可以先占(中断)。
可以在其他线程正在运行时将其暂时置于暂挂状态(也称为休眠)-这称为yield。
有两种不同的线程-
内核线程是操作系统的一部分,而用户空间线程未在内核中实现。
有两个模块支持在Python3中使用线程-
线程模块已被“弃用”了很长时间。鼓励用户改用线程模块。因此,在Python 3中,模块“线程”不再可用。但是,由于Python3中的向后兼容性,它已重命名为“ _thread”。
要生成另一个线程,您需要调用线程模块中可用的以下方法-
_thread.start_new_thread ( function, args[, kwargs] )
通过此方法调用,可以快速有效地在Linux和Windows中创建新线程。
方法调用立即返回,子线程启动,并使用传递的args列表调用函数。当函数返回时,线程终止。
在这里, args是参数的元组;使用一个空的元组调用函数而不传递任何参数。 kwargs是关键字参数的可选字典。
#!/usr/bin/python3
import _thread
import time
# Define a function for the thread
def print_time( threadName, delay):
count = 0
while count < 5:
time.sleep(delay)
count += 1
print ("%s: %s" % ( threadName, time.ctime(time.time()) ))
# Create two threads as follows
try:
_thread.start_new_thread( print_time, ("Thread-1", 2, ) )
_thread.start_new_thread( print_time, ("Thread-2", 4, ) )
except:
print ("Error: unable to start thread")
while 1:
pass
执行以上代码后,将产生以下结果-
Thread-1: Fri Feb 19 09:41:39 2016
Thread-2: Fri Feb 19 09:41:41 2016
Thread-1: Fri Feb 19 09:41:41 2016
Thread-1: Fri Feb 19 09:41:43 2016
Thread-2: Fri Feb 19 09:41:45 2016
Thread-1: Fri Feb 19 09:41:45 2016
Thread-1: Fri Feb 19 09:41:47 2016
Thread-2: Fri Feb 19 09:41:49 2016
Thread-2: Fri Feb 19 09:41:53 2016
程序陷入无限循环。您将必须按ctrl-c才能停止
尽管它对于低级线程非常有效,但是与更新的线程模块相比,线程模块非常有限。
与上一节中讨论的线程模块相比, Python 2.4中包含的更新的线程模块为线程提供了更强大的高级支持。
threading模块暴露出线程模块的所有方法,并提供了一些额外的方法-
threading.activeCount() -返回活动的线程对象数。
threading.currentThread() -返回调用者的线程控件中线程对象的数量。
threading.enumerate() -返回当前处于活动状态的所有线程对象的列表。
除了这些方法之外,线程模块还具有实现线程的Thread类。 Thread类提供的方法如下-
run() -run()方法是线程的入口点。
start() -start()方法通过调用run方法来启动线程。
join([time]) -join()等待线程终止。
isAlive() -isAlive()方法检查线程是否仍在执行。
getName() -getName()方法返回线程的名称。
setName() -setName()方法设置线程的名称。
要使用线程模块实现新线程,您必须执行以下操作-
定义Thread类的新子类。
重写__init __(self [,args])方法以添加其他参数。
然后,重写run(self [,args])方法以实现线程在启动时应执行的操作。
一旦创建了新的Thread子类,就可以创建它的实例,然后通过调用start()来启动新线程,该start()依次调用run()方法。
#!/usr/bin/python3
import threading
import time
exitFlag = 0
class myThread (threading.Thread):
def __init__(self, threadID, name, counter):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.counter = counter
def run(self):
print ("Starting " + self.name)
print_time(self.name, self.counter, 5)
print ("Exiting " + self.name)
def print_time(threadName, delay, counter):
while counter:
if exitFlag:
threadName.exit()
time.sleep(delay)
print ("%s: %s" % (threadName, time.ctime(time.time())))
counter -= 1
# Create new threads
thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)
# Start new Threads
thread1.start()
thread2.start()
thread1.join()
thread2.join()
print ("Exiting Main Thread")
当我们运行上面的程序时,它将产生以下结果-
Starting Thread-1
Starting Thread-2
Thread-1: Fri Feb 19 10:00:21 2016
Thread-2: Fri Feb 19 10:00:22 2016
Thread-1: Fri Feb 19 10:00:22 2016
Thread-1: Fri Feb 19 10:00:23 2016
Thread-2: Fri Feb 19 10:00:24 2016
Thread-1: Fri Feb 19 10:00:24 2016
Thread-1: Fri Feb 19 10:00:25 2016
Exiting Thread-1
Thread-2: Fri Feb 19 10:00:26 2016
Thread-2: Fri Feb 19 10:00:28 2016
Thread-2: Fri Feb 19 10:00:30 2016
Exiting Thread-2
Exiting Main Thread
Python随附的线程模块包括一种易于实现的锁定机制,可让您同步线程。通过调用Lock()方法创建一个新锁,该方法返回新锁。
新锁对象的acquire(blocking)方法用于强制线程同步运行。可选的阻塞参数使您可以控制线程是否等待获取锁。
如果将blocking设置为0,则如果无法获取锁,则线程立即返回0值,如果获取锁,则线程返回1。如果将阻塞设置为1,则线程将阻塞并等待释放锁。
新的锁对象的release()方法用于在不再需要时释放锁。
#!/usr/bin/python3
import threading
import time
class myThread (threading.Thread):
def __init__(self, threadID, name, counter):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.counter = counter
def run(self):
print ("Starting " + self.name)
# Get lock to synchronize threads
threadLock.acquire()
print_time(self.name, self.counter, 3)
# Free lock to release next thread
threadLock.release()
def print_time(threadName, delay, counter):
while counter:
time.sleep(delay)
print ("%s: %s" % (threadName, time.ctime(time.time())))
counter -= 1
threadLock = threading.Lock()
threads = []
# Create new threads
thread1 = myThread(1, "Thread-1", 1)
thread2 = myThread(2, "Thread-2", 2)
# Start new Threads
thread1.start()
thread2.start()
# Add threads to thread list
threads.append(thread1)
threads.append(thread2)
# Wait for all threads to complete
for t in threads:
t.join()
print ("Exiting Main Thread")
执行以上代码后,将产生以下结果-
Starting Thread-1
Starting Thread-2
Thread-1: Fri Feb 19 10:04:14 2016
Thread-1: Fri Feb 19 10:04:15 2016
Thread-1: Fri Feb 19 10:04:16 2016
Thread-2: Fri Feb 19 10:04:18 2016
Thread-2: Fri Feb 19 10:04:20 2016
Thread-2: Fri Feb 19 10:04:22 2016
Exiting Main Thread
队列模块允许您创建一个可以容纳特定数量项目的新队列对象。有以下方法来控制队列-
get() -get()从队列中删除并返回一个项目。
put() -put将项目添加到队列。
qsize() -qsize()返回队列中当前的项目数。
empty() -如果队列为空,则Empty()返回True;否则,返回true。否则为False。
full() -如果队列已满,则full()返回True;否则,返回true。否则为False。
#!/usr/bin/python3
import queue
import threading
import time
exitFlag = 0
class myThread (threading.Thread):
def __init__(self, threadID, name, q):
threading.Thread.__init__(self)
self.threadID = threadID
self.name = name
self.q = q
def run(self):
print ("Starting " + self.name)
process_data(self.name, self.q)
print ("Exiting " + self.name)
def process_data(threadName, q):
while not exitFlag:
queueLock.acquire()
if not workQueue.empty():
data = q.get()
queueLock.release()
print ("%s processing %s" % (threadName, data))
else:
queueLock.release()
time.sleep(1)
threadList = ["Thread-1", "Thread-2", "Thread-3"]
nameList = ["One", "Two", "Three", "Four", "Five"]
queueLock = threading.Lock()
workQueue = queue.Queue(10)
threads = []
threadID = 1
# Create new threads
for tName in threadList:
thread = myThread(threadID, tName, workQueue)
thread.start()
threads.append(thread)
threadID += 1
# Fill the queue
queueLock.acquire()
for word in nameList:
workQueue.put(word)
queueLock.release()
# Wait for queue to empty
while not workQueue.empty():
pass
# Notify threads it's time to exit
exitFlag = 1
# Wait for all threads to complete
for t in threads:
t.join()
print ("Exiting Main Thread")
执行以上代码后,将产生以下结果-
Starting Thread-1
Starting Thread-2
Starting Thread-3
Thread-1 processing One
Thread-2 processing Two
Thread-3 processing Three
Thread-1 processing Four
Thread-2 processing Five
Exiting Thread-3
Exiting Thread-1
Exiting Thread-2
Exiting Main Thread