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Parallel printing and write lock


Parallel printing and write lock

By : user6064217
Date : November 20 2020, 11:01 PM
Hope that helps This might be a problem with the global lock variable. When you are creating the child process in unix you have a copy of the memory of the parent. In windows it seems that it not the case
Try this code
code :
from __future__ import division
import os, sys
import signal
from time import sleep
from multiprocessing import Pool, freeze_support, Lock

if os.name == 'nt':
    import colorama  # to support cursor up
    colorama.init()

_term_move_up = '\x1b[A'



class simple_bar(object):
    def __init__(self, iterable, desc='', position=0):
        signal.signal(signal.SIGINT, signal.SIG_IGN)  # handles keyboardinterrupt
        self.iterable = iterable
        self.total = len(iterable)
        self.n = 0
        self.position = position
        self.desc = desc
        self.display()

    def __iter__(self):
        for obj in self.iterable:
            yield obj
            self.update()

    def update(self, n=1):
        self.n += n
        self.display()

    def display(self, fp=None, width=79):
        if not fp:
            fp = sys.stdout

        with write_lock:
            fp.write('\n' * self.position)
            l_part = self.desc + ': '
            bar = l_part + '#' * int((self.n / self.total) * (width - len(l_part)))
            fp.write('\r' + bar + ' ' * (width - len(bar)))
            fp.write(_term_move_up * self.position)
            fp.flush()

def progresser(n):
    text = "progresser #{}".format(n)
    for i in simple_bar(range(5000), desc=text, position=n):
        sleep(0.001)

def init_child(lock_):
    global write_lock
    write_lock = lock_

if __name__ == '__main__':
    write_lock = Lock()
    L = list(range(3))
    pool = Pool(len(L), initializer=init_child, initargs=(write_lock,))
    pool.map(progresser, L)


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pthreads: reader/writer locks, upgrading read lock to write lock

pthreads: reader/writer locks, upgrading read lock to write lock


By : smile
Date : March 29 2020, 07:55 AM
I wish did fix the issue. What else than a dead lock do you want in the following scenario?
thread 1 acquire read lock thread 2 acquire read lock thread 1 ask to upgrade lock to write thread 2 ask to upgrade lock to write
Obtaining Read/Write Lock for Sqlite Parallel Updates

Obtaining Read/Write Lock for Sqlite Parallel Updates


By : Greg Besso
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I write a lot of parallel scripts in python for research purposes and was wondering if it is possible to obtain a read/write lock manually in sqlite for a specific set of commands. Here is an oversimplified example of why I need it: , You can increment an integer value using a single UPDATE statement:
code :
sqlite> CREATE TABLE B(Id INTEGER, Value INTEGER);
sqlite> INSERT INTO B VALUES(0, 15);
sqlite> UPDATE B SET Value=Value + 23 WHERE Id = 0;
sqlite> SELECT * FROM B;
0|38
sqlite> 
sqlite> CREATE TABLE C(Id INTEGER, Value TEXT);
sqlite> INSERT INTO C VALUES(0, 'X');
sqlite> UPDATE C SET Value=Value || 'Y' WHERE Id = 0;
sqlite> SELECT * FROM C;
0|XY
sqlite> 
Python : Any way to get one process to have a write lock and others to just read on parallel?

Python : Any way to get one process to have a write lock and others to just read on parallel?


By : Srihari Thekumparamb
Date : March 29 2020, 07:55 AM
help you fix your problem I found these python version of the reader writer lock
A reader-writer lock for Python
PThreads: Read/Write Lock: How to check if thread holds the write lock?

PThreads: Read/Write Lock: How to check if thread holds the write lock?


By : Hoàng Xuân Sơn
Date : March 29 2020, 07:55 AM
To fix this issue Your wrapper should keep track of whether it already has the write lock held in that thread. You can do this in a number of ways, but looking at how popular libraries ilke boost or ACE do it would probably help.
You should consider using one of those existing libraries and skip the worries and effort of re-implementing what has probably been done before.
Documentation contradictions about ReentrantReadWriteLock. Does eventually write lock has priority over read lock or not

Documentation contradictions about ReentrantReadWriteLock. Does eventually write lock has priority over read lock or not


By : Adam Therazy
Date : March 29 2020, 07:55 AM
hop of those help? Here, quoting from your quote:
or if there is a group of reader threads
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