python队列多线程

Question

What is the simplest way to have only two trains(in the same time) on the railroad. My english is bad. this is only way how I can explain it. I know I should use Queue? I can't find info in my language

Thank you!

1>go, 2>go. 3,4wait. 1>finish, 3>go (4th still wait) ..

from threading import Thread
import time
import random

def trains(city):
    print city, 'start'

    for count in range(1,3):
        delay = random.randrange(5,10)
        print city, 'delay', delay
        time.sleep(delay)

    print city, 'end'


cities = ['prague', 'london', 'berlin', 'moscow']
threadlist = []

for city in cities:                             
    t = Thread(target=trains, args=(city,))
    t.start()
    threadlist.append(t)


for b in threadlist:
    b.join()

Answer 1

I'm going to guess at some things here:

from threading import Thread, Lock, BoundedSemaphore
import time
import random

def trains(city):
    with railroads:
        with iolock:
            print city, 'start'

        for count in range(1,3):
            delay = random.randrange(5,10)
            with iolock:
                print city, 'delay', delay
            time.sleep(delay)

        with iolock:
            print city, 'end'


cities = ['prague', 'london', 'berlin', 'moscow']
threadlist = []

iolock = Lock()
railroads = BoundedSemaphore(2)

for city in cities:                             
    t = Thread(target=trains, args=(city,))
    t.start()
    threadlist.append(t)


for b in threadlist:
    b.join()

The purpose of iolock is to stop mixed-up output in your terminal: only 1 thread prints at a time. The purpose of railroads is to allow at most two threads to enter the body of the code simultaneously. Here's sample output. Note that "prague" and "london" happen to run at first, but "berlin" doesn't start before "london" ends. Then "moscow" doesn't start until "prague" ends:

prague start
london start
prague delay 8
london delay 5
london delay 6
prague delay 5
london end
berlin start
berlin delay 8
prague end
moscow start
moscow delay 8
berlin delay 6
moscow delay 7
berlin end
moscow end