【Python学习之路】——Day10(线程、进程)
Python线程
Threading用于提供线程相关的操作,线程是应用程序中工作的最小单元。
#!/usr/bin/env python # -*- coding:utf-8 -*- import threading import time def show(arg): time.sleep(1) print 'thread'+str(arg) for i in range(10): t = threading.Thread(target=show, args=(i,)) t.start() print 'main thread stop'
上述代码创建了10个“前台”线程,然后控制器就交给了CPU,CPU根据指定算法进行调度,分片执行指令。
更多方法:
- start 线程准备就绪,等待CPU调度
- setName 为线程设置名称
- getName 获取线程名称
- setDaemon 设置为后台线程或前台线程(默认)
如果是后台线程,主线程执行过程中,后台线程也在进行,主线程执行完毕后,后台线程不论成功与否,均停止
如果是前台线程,主线程执行过程中,前台线程也在进行,主线程执行完毕后,等待前台线程也执行完成后,程序停止 - join 逐个执行每个线程,执行完毕后继续往下执行,该方法使得多线程变得无意义
- run 线程被cpu调度后自动执行线程对象的run方法
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import threading import time class MyThread(threading.Thread): def __init__(self,num): threading.Thread.__init__(self) self.num = num def run(self):#定义每个线程要运行的函数 print("running on number:%s" %self.num) time.sleep(3) if __name__ == '__main__': t1 = MyThread(1) t2 = MyThread(2) t1.start() t2.start()
线程锁(Lock、RLock)
由于线程之间是进行随机调度,并且每个线程可能只执行n条执行之后,当多个线程同时修改同一条数据时可能会出现脏数据,所以,出现了线程锁 - 同一时刻允许一个线程执行操作。
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#!/usr/bin/env python # -*- coding:utf-8 -*- import threading import time gl_num = 0 def show(arg): global gl_num time.sleep(1) gl_num +=1 print gl_num for i in range(10): t = threading.Thread(target=show, args=(i,)) t.start() print 'main thread stop'
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#!/usr/bin/env python #coding:utf-8 import threading import time gl_num = 0 lock = threading.RLock() def Func(): lock.acquire() global gl_num gl_num +=1 time.sleep(1) print gl_num lock.release() for i in range(10): t = threading.Thread(target=Func) t.start()
信号量(Semaphore)
互斥锁 同时只允许一个线程更改数据,而Semaphore是同时允许一定数量的线程更改数据 ,比如厕所有3个坑,那最多只允许3个人上厕所,后面的人只能等里面有人出来了才能再进去。
import threading,time def run(n): semaphore.acquire() time.sleep(1) print("run the thread: %s" %n) semaphore.release() if __name__ == '__main__': num= 0 semaphore = threading.BoundedSemaphore(5) #最多允许5个线程同时运行 for i in range(20): t = threading.Thread(target=run,args=(i,)) t.start()
事件(event)
python线程的事件用于主线程控制其他线程的执行,事件主要提供了三个方法 set、wait、clear。
事件处理的机制:全局定义了一个“Flag”,如果“Flag”值为 False,那么当程序执行 event.wait 方法时就会阻塞,如果“Flag”值为True,那么event.wait 方法时便不再阻塞。
- clear:将“Flag”设置为False
- set:将“Flag”设置为True
#!/usr/bin/env python # -*- coding:utf-8 -*- import threading def do(event): print 'start' event.wait() print 'execute' event_obj = threading.Event() for i in range(10): t = threading.Thread(target=do, args=(event_obj,)) t.start() event_obj.clear() inp = raw_input('input:') if inp == 'true': event_obj.set()
条件(Condition)
使得线程等待,只有满足某条件时,才释放n个线程
import threading def run(n): con.acquire() con.wait() print("run the thread: %s" %n) con.release() if __name__ == '__main__': con = threading.Condition() for i in range(10): t = threading.Thread(target=run, args=(i,)) t.start() while True: inp = input('>>>') if inp == 'q': break con.acquire() con.notify(int(inp)) con.release()
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def condition_func(): ret = False inp = input('>>>') if inp == '1': ret = True return ret def run(n): con.acquire() con.wait_for(condition_func) print("run the thread: %s" %n) con.release() if __name__ == '__main__': con = threading.Condition() for i in range(10): t = threading.Thread(target=run, args=(i,)) t.start()
Timer
定时器,指定n秒后执行某操作
from threading import Timer def hello(): print("hello, world") t = Timer(1, hello) t.start() # after 1 seconds, "hello, world" will be printed
queue队列
queue is especially useful in threaded programming when information must be exchanged safely between multiple threads.
- class
queue.
Queue
(maxsize=0) #先入先出
- class
queue.
LifoQueue
(maxsize=0) #last in fisrt out - class
queue.
PriorityQueue
(maxsize=0) #存储数据时可设置优先级的队列
-
Constructor for a priority queue. maxsize is an integer that sets the upperbound limit on the number of items that can be placed in the queue. Insertion will block once this size has been reached, until queue items are consumed. If maxsize is less than or equal to zero, the queue size is infinite.
The lowest valued entries are retrieved first (the lowest valued entry is the one returned by
sorted(list(entries))[0]
). A typical pattern for entries is a tuple in the form:(priority_number, data)
.
- exception
queue.
Empty
-
Exception raised when non-blocking
get()
(orget_nowait()
) is called on aQueue
object which is empty.
- exception
queue.
Full
-
Exception raised when non-blocking
put()
(orput_nowait()
) is called on aQueue
object which is full.
Queue.
qsize
()
Queue.
empty
() #return True if empty
Queue.
full
() # return True if full
Queue.
put
(item, block=True, timeout=None)-
Put item into the queue. If optional args block is true and timeout is None (the default), block if necessary until a free slot is available. If timeout is a positive number, it blocks at most timeout seconds and raises the
Full
exception if no free slot was available within that time. Otherwise (block is false), put an item on the queue if a free slot is immediately available, else raise theFull
exception (timeout is ignored in that case).
Queue.
put_nowait
(item)-
Equivalent to
put(item, False)
.
Queue.
get
(block=True, timeout=None)-
Remove and return an item from the queue. If optional args block is true and timeout is None (the default), block if necessary until an item is available. If timeout is a positive number, it blocks at most timeout seconds and raises the
Empty
exception if no item was available within that time. Otherwise (block is false), return an item if one is immediately available, else raise theEmpty
exception (timeout is ignored in that case).
Queue.
get_nowait
()-
Equivalent to
get(False)
.
Two methods are offered to support tracking whether enqueued tasks have been fully processed by daemon consumer threads.
Queue.
task_done
()-
Indicate that a formerly enqueued task is complete. Used by queue consumer threads. For each
get()
used to fetch a task, a subsequent call totask_done()
tells the queue that the processing on the task is complete.If a
join()
is currently blocking, it will resume when all items have been processed (meaning that atask_done()
call was received for every item that had beenput()
into the queue).Raises a
ValueError
if called more times than there were items placed in the queue.
Queue.
join
() block直到queue被消费完毕
生产者消费者模型
在并发编程中使用生产者和消费者模式能够解决绝大多数并发问题。该模式通过平衡生产线程和消费线程的工作能力来提高程序的整体处理数据的速度。
为什么要使用生产者和消费者模式
在线程世界里,生产者就是生产数据的线程,消费者就是消费数据的线程。在多线程开发当中,如果生产者处理速度很快,而消费者处理速度很慢,那么生产者就必须等待消费者处理完,才能继续生产数据。同样的道理,如果消费者的处理能力大于生产者,那么消费者就必须等待生产者。为了解决这个问题于是引入了生产者和消费者模式。
什么是生产者消费者模式
生产者消费者模式是通过一个容器来解决生产者和消费者的强耦合问题。生产者和消费者彼此之间不直接通讯,而通过阻塞队列来进行通讯,所以生产者生产完数据之后不用等待消费者处理,直接扔给阻塞队列,消费者不找生产者要数据,而是直接从阻塞队列里取,阻塞队列就相当于一个缓冲区,平衡了生产者和消费者的处理能力。
下面来学习一个最基本的生产者消费者模型的例子
import threading import queue def producer(): for i in range(10): q.put("骨头 %s" % i ) print("开始等待所有的骨头被取走...") q.join() print("所有的骨头被取完了...") def consumer(n): while q.qsize() >0: print("%s 取到" %n , q.get()) q.task_done() #告知这个任务执行完了 q = queue.Queue() p = threading.Thread(target=producer,) p.start() c1 = consumer("李闯")
import time,random import queue,threading q = queue.Queue() def Producer(name): count = 0 while count <20: time.sleep(random.randrange(3)) q.put(count) print('Producer %s has produced %s baozi..' %(name, count)) count +=1 def Consumer(name): count = 0 while count <20: time.sleep(random.randrange(4)) if not q.empty(): data = q.get() print(data) print('\033[32;1mConsumer %s has eat %s baozi...\033[0m' %(name, data)) else: print("-----no baozi anymore----") count +=1 p1 = threading.Thread(target=Producer, args=('A',)) c1 = threading.Thread(target=Consumer, args=('B',)) p1.start() c1.start()
Python 进程
from multiprocessing import Process import threading import time def foo(i): print 'say hi',i for i in range(10): p = Process(target=foo,args=(i,)) p.start()
注意:由于进程之间的数据需要各自持有一份,所以创建进程需要的非常大的开销。
多进程multiprocessing
multiprocessing
is a package that supports spawning processes using an API similar to the threading
module. The multiprocessing
package offers both local and remote concurrency, effectively side-stepping the Global Interpreter Lock by using subprocesses instead of threads. Due to this, the multiprocessing
module allows the programmer to fully leverage multiple processors on a given machine. It runs on both Unix and Windows.
from multiprocessing import Process import time def f(name): time.sleep(2) print('hello', name) if __name__ == '__main__': p = Process(target=f, args=('bob',)) p.start() p.join()
To show the individual process IDs involved, here is an expanded example:
from multiprocessing import Process import os def info(title): print(title) print('module name:', __name__) print('parent process:', os.getppid()) print('process id:', os.getpid()) print("\n\n") def f(name): info('\033[31;1mfunction f\033[0m') print('hello', name) if __name__ == '__main__': info('\033[32;1mmain process line\033[0m') p = Process(target=f, args=('bob',)) p.start() p.join()
进程间通讯
不同进程间内存是不共享的,要想实现两个进程间的数据交换,可以用以下方法:
Queues
使用方法跟threading里的queue差不多
from multiprocessing import Process, Queue def f(q): q.put([42, None, 'hello']) if __name__ == '__main__': q = Queue() p = Process(target=f, args=(q,)) p.start() print(q.get()) # prints "[42, None, 'hello']" p.join()
Pipes
The Pipe()
function returns a pair of connection objects connected by a pipe which by default is duplex (two-way). For example:
from multiprocessing import Process, Pipe def f(conn): conn.send([42, None, 'hello']) conn.close() if __name__ == '__main__': parent_conn, child_conn = Pipe() p = Process(target=f, args=(child_conn,)) p.start() print(parent_conn.recv()) # prints "[42, None, 'hello']" p.join()
进程数据共享
进程各自持有一份数据,默认无法共享数据
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#!/usr/bin/env python #coding:utf-8 from multiprocessing import Process from multiprocessing import Manager import time li = [] def foo(i): li.append(i) print 'say hi',li for i in range(10): p = Process(target=foo,args=(i,)) p.start() print 'ending',li
#方法一,Array from multiprocessing import Process,Array temp = Array('i', [11,22,33,44]) def Foo(i): temp[i] = 100+i for item in temp: print i,'----->',item for i in range(2): p = Process(target=Foo,args=(i,)) p.start() #方法二:manage.dict()共享数据 from multiprocessing import Process,Manager manage = Manager() dic = manage.dict() def Foo(i): dic[i] = 100+i print dic.values() for i in range(2): p = Process(target=Foo,args=(i,)) p.start() p.join()
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'c': ctypes.c_char, 'u': ctypes.c_wchar, 'b': ctypes.c_byte, 'B': ctypes.c_ubyte, 'h': ctypes.c_short, 'H': ctypes.c_ushort, 'i': ctypes.c_int, 'I': ctypes.c_uint, 'l': ctypes.c_long, 'L': ctypes.c_ulong, 'f': ctypes.c_float, 'd': ctypes.c_double
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from multiprocessing import Process, Queue def f(i,q): print(i,q.get()) if __name__ == '__main__': q = Queue() q.put("h1") q.put("h2") q.put("h3") for i in range(10): p = Process(target=f, args=(i,q,)) p.start()
进程池
进程池内部维护一个进程序列,当使用时,则去进程池中获取一个进程,如果进程池序列中没有可供使用的进进程,那么程序就会等待,直到进程池中有可用进程为止。
进程池中有两个方法:
- apply
- apply_async
#!/usr/bin/env python # -*- coding:utf-8 -*- from multiprocessing import Process,Pool import time def Foo(i): time.sleep(2) return i+100 def Bar(arg): print arg pool = Pool(5) #print pool.apply(Foo,(1,)) #print pool.apply_async(func =Foo, args=(1,)).get() for i in range(10): pool.apply_async(func=Foo, args=(i,),callback=Bar) print 'end' pool.close() pool.join()#进程池中进程执行完毕后再关闭,如果注释,那么程序直接关闭。
参考:http://www.cnblogs.com/wupeiqi/articles/5040827.html