CODEWITHSUNDEEP
pythonmultithreading
Searene
Searene

Reputation: 27544

How to use multiple threads

I have this code:

import thread

def print_out(m1, m2):
    print m1
    print m2
    print "\n"

for num in range(0, 10):
    thread.start_new_thread(print_out, ('a', 'b'))

I want to create 10 threads, each thread runs the function print_out, but I failed. The errors are as follows:

Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr
Unhandled exception in thread started by 
sys.excepthook is missing
lost sys.stderr

Upvotes: 16

Views: 23703

Answers (5)

Firebird
Firebird

Reputation: 1

Whenever you are creating thread you need to run main thread before that. Here you are not running any main tread.

To solve the problem you can add a print statement of any other statement. Lets modify your code

import thread
import time

def print_out(m1, m2):
    print m1
    print m2
    print "\n"

for num in range(0, 10):
    thread.start_new_thread(print_out, ('a', 'b'))
    time.sleep(.1)

Here time.sleep() is creating main tread for you and thread.start_new_thread creating 10 threads on the main tread. Note: You can add any statement in place of time.sleep()

Upvotes: 0

R. NG
R. NG

Reputation: 11

Using thread module, you need to have a main thread running, by adding a while loop below

import thread

def print_out(m1, m2):
    print m1
    print m2
    print "\n"

for num in range(0, 10):
    thread.start_new_thread(print_out, ('a', 'b'))`

while(1):
    pass

Upvotes: 1

lijian
lijian

Reputation: 21

The other approach is using threading class.

 instance[num]=threading.Thread(target=print_out, args=('a', 'b'))

 instance[num].start()

Upvotes: 2

David Heffernan
David Heffernan

Reputation: 612794

First of all, you should use the higher level threading module and specifically the Thread class. The thread module is not what you need.

As you extend this code, you most likely will also want to wait for the threads to finish. Following is a demonstration of how to use the join method to achieve that:

import threading

class print_out(threading.Thread):

    def __init__ (self, m1, m2):
        threading.Thread.__init__(self)
        self.m1 = m1
        self.m2 = m2

    def run(self):
        print self.m1
        print self.m2
        print "\n"

threads = []
for num in range(0, 10):
    thread = print_out('a', 'b')
    thread.start()
    threads.append(thread)

for thread in threads:
    thread.join()

Upvotes: 13

Phani
Phani

Reputation: 3315

You should let the main thread stay alive for a little while. If the main thread dies, so will all the other threads and hence you will not see any output. Try adding a time.sleep(0.1) at the end of the code and then you will see the output.

After that, you can have a look at the thread.join() to get more idea about this.

Upvotes: 2

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