Barrier provides one of the python synchronization technique with which single or multiple threads wait until a point in a set of activities and make progress together.
To define a barrier object, “threading. Barrier” is used.
threading.Barrier(parties, action = None, timeout = None)
Where,
parties = Number of threads
action = called by one of the threads when they are released.
timeout = Default timeout value. In case no timeout value is specified for the wait(), this timeout value is used.
Below mentioned methods are used by Barrier class.
| Sr.No | Method & Description |
|---|---|
| 1 | parties A number of threads required to reach the common barrier point. |
| 2 | n_waiting Number of threads waiting in the common barrier point |
| 3 | broken A boolean value, True- if the barrier is in the broken state else False. |
| 4 | wait( timeout = None) Wait until notified or a timeout occurs. If the calling thread has not acquired the lock when this method is called, a runtime error is raised. This method releases the underlying lock and then blocks until it is awakened by a notify() or notify_all() method call for the same condition variable in another thread, or until the optional timeout occurs. Once awakened or timed out, it re-acquires the lock and returns. When the timeout argument is present and not None, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof). |
| 5 | reset() Set or return the barrier to the default state .i.e. empty state. And threads waiting on it will receive the BrokenBarrierError. |
| 6 | Abort() This will put the barrier into a broken state. This causes all the active threads or any future calls to wait() to fail with the BrokenBarrierError. |
barrierThread.py
from random import randrange
from threading import Barrier, Thread
from time import ctime, sleep
num = 4
# 4 threads will need to pass this barrier to get released.
b = Barrier(num)
names = ['India', 'Japan', 'USA', 'China']
def player():
name = names.pop()
sleep(randrange(2, 5))
print('%s reached the barrier at: %s \n' % (name, ctime()))
b.wait()
threads = []
print("Race starts now…")
for i in range(num):
threads.append(Thread(target=player))
threads[-1].start()
"""
Below loop enables waiting for the threads to complete before moving on with the main script.
"""
for thread in threads:
thread.join()
print("All Reached Barrier Point!")Result
Race starts now… India reached the barrier at: Fri Jan 18 14:07:44 2019 China reached the barrier at: Fri Jan 18 14:07:44 2019 Japan reached the barrier at: Fri Jan 18 14:07:46 2019 USA reached the barrier at: Fri Jan 18 14:07:46 2019 All Reached Barrier Point!