Python的进程和线程（2）

1. Python中的线程

Thread类
t = threading.Thread(target=None,name=None,args=(),kwargs=None,*,daemin=None)

target:线程调用的对象，目标函数
name：线程的名字，可以重名
args：目标函数传参，元祖
kwargs：传递关键字参数，字典

import threading
import  time

def worker():
    for _ in range(3):
        time.sleep(0.5)
        print("welcome mykernel")
        print("therad over")

def worker1():
    for _ in range(3):
        time.sleep(0.5)
        print("welcome mykernel......")
        print("therad over ..........")

t = threading.Thread(target=worker,name='w1')
t1 = threading.Thread(target=worker1,name='w2')
t.start()
t1.start()

welcome mykernel
therad over
welcome mykernel......
therad over ..........
welcome mykernel
therad over
welcome mykernel......
therad over ..........
welcome mykernel
therad over
welcome mykernel......
therad over ..........

python线程的没有特定的退出方法，
常见的退出：

1. 线程函数内语句执行完成
2. 线程函数中抛出未处理的异常

import threading
import  time

def worker():
    count = 0
    for _ in range(10):
        time.sleep(0.5)
        print("welcome mykernel")
        count +=1
        if count >4:
            raise Exception("count大于4异常")

t = threading.Thread(target=worker,name='w1')
t.start()

welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel


Exception in thread w1:
Traceback (most recent call last):
  File "/root/.pyenv/versions/3.7.3/lib/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/root/.pyenv/versions/3.7.3/lib/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "<ipython-input-9-0fc2f50f7f96>", line 11, in worker
    raise Exception("count大于4异常")
Exception: count大于4异常

Python中的线程无优先级和线程组概念，不能被销毁、停止、挂起和恢复。

1. Thread传入参数

import threading
import  time

def worker(n):
    count = 0
    for _ in range(n):
        time.sleep(0.5)
        print("welcome mykernel")
        count +=1
        if count >4:
            raise Exception("count大于4异常")

t = threading.Thread(target=worker,name='w1',args=(5,))
t.start()

welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel


Exception in thread w1:
Traceback (most recent call last):
  File "/root/.pyenv/versions/3.7.3/lib/python3.7/threading.py", line 917, in _bootstrap_inner
    self.run()
  File "/root/.pyenv/versions/3.7.3/lib/python3.7/threading.py", line 865, in run
    self._target(*self._args, **self._kwargs)
  File "<ipython-input-4-36a6bbbdc89d>", line 11, in worker
    raise Exception("count大于4异常")
Exception: count大于4异常

2. threading的属性和方法

current_thread():返回当前线程对象
main_thread()：返回主线程对象
active_thread()：当前处于alive状态的线程个数
enumerate()：返回所有活着的线程的列表，不包含已经终止和未开始的线程
get_ident()：返回当前线程id飞0整数

import threading
import  time

def worker(n):
    # 打印当前的线程
    print(threading.current_thread())
    # 打印该线程的主进程
    print(threading.main_thread())
    # 打印活着的进程数
    print(threading.active_count())
    # 打印活着进程的列表
    print(threading.enumerate())
    for _ in range(n):
        time.sleep(0.5)
        print("welcome mykernel")

print(threading.current_thread())
t = threading.Thread(target=worker,name='w1',args=(5,))
t.start()

print("T....",threading.enumerate(),'/n')

<_MainThread(MainThread, started 140182288873280)>
<Thread(w1, started 140181357197056)>
<_MainThread(MainThread, started 140182288873280)>
6
[<_MainThread(MainThread, started 140182288873280)>, <Thread(Thread-2, started daemon 140181894067968)>, <Heartbeat(Thread-3, started daemon 140181885675264)>, <HistorySavingThread(IPythonHistorySavingThread, started 140181860497152)>, <ParentPollerUnix(Thread-1, started daemon 140181851318016)>, <Thread(w1, started 140181357197056)>]
T.... [<_MainThread(MainThread, started 140182288873280)>, <Thread(Thread-2, started daemon 140181894067968)>, <Heartbeat(Thread-3, started daemon 140181885675264)>, <HistorySavingThread(IPythonHistorySavingThread, started 140181860497152)>, <ParentPollerUnix(Thread-1, started daemon 140181851318016)>, <Thread(w1, started 140181357197056)>] /n
welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel
welcome mykernel

3. thread实例的属性和方法

name ：名字标识，可以重名，使用getName(),setName()获取和设置
ident:线程id，是非0 整数，线程启动后才有id，否则为None，线程退出，此id依然可以访问，id可以重复使用
is_alive() 返回线程是否活着

import threading
import  time

def worker():
    count = 0
    while True:
        if (count>4):
            break
        time.sleep(0.5)
        count +=1

        print(threading.current_thread().name)
        print(threading.current_thread().ident)

t = threading.Thread(name='worker',target=worker())
t.start()
for _ in range(3):
    time.sleep(1)
    if t.is_alive():
        print('{} {} alive'.format(t.name,t.ident))
    else:
        print('{} {} dead'.format(t.name, t.ident))

MainThread
139942493099840
MainThread
139942493099840
MainThread
139942493099840
MainThread
139942493099840
MainThread
139942493099840
worker 139941778028288 dead
worker 139941778028288 dead
worker 139941778028288 dead

start() 启动线程，每一个线程必须且只能执行一次该方法
run() 运行线程函数