RedLock

When a user clicks on the Break button, it executes the Break() function inside the JS. It then calls getData() and also 2 lines of code after getData with CSS. But if you see that 2 CSS btnLock which use to hide lock.png and btnUnlock which displays unlock.png. it is not waiting for getData() to complete and these 2 CSS is getting overridden with what we have in buildTable(). So the option I am looking for is to build the datatable medTable.draw() first and then check if the Break() has completed. If so, then use these 2 CSS to hide and display.

So for that, I want to use the global boolean variable to store the status of the Break function. I mean whether it completed or not so that I can use it after medTable.draw(); to check the Break function completed.

Index

I try to build a redis cluster follow this cluster-tutorial

I try to use this tutorial(RedLock) to write codeRed Lock

Got the following error ： terminate called after throwing an instance of 'sw::redis::MovedError'

I am looking for a readers-writer lock that can be used in python in a distributed system.

So far I've found:

1. redlock, which is based on redis. Does not provide a readers-writer lock.
2. The distributed package of dask offers a lock, but again, no readers-writer lock.
3. kazoo, which works with Zookeeper, offers a readers-writer lock. However Zookeeper is an extremely heavy dependency, as it written in Java and therefore requires the JDK.

Is there a more lightweight alternative to kazoo / Zookeeper? Ideally a pure python solution that is nevertheless battle tested?

Is Redisson's getLock() method good for a distributed use case, and how does it compare to getRedLock()?

Redisson (3.11.x) has several methods to instantiate locks:

• RedissonClient.getLock()
• RedissonClient.getRedLock()
• others like getReadWriteLock(), getFairLock(), etc.

What algorithm does getLock() use, and is it safe for distributed usage? The documentation says:

Implements a non-fair locking so doesn't guarantees an acquire order by threads.

I am looking to compare getLock() to getRedLock(), which appears to use Redlock and is documented at the top-level of Redis' distlock page: https://redis.io/topics/distlock:

This page is an attempt to provide a more canonical algorithm to implement distributed locks with Redis. We propose an algorithm, called Redlock, which implements a DLM which we believe to be safer than the vanilla single instance approach.

I have a Redis cluster of 3 master nodes and each master has corresponding slave nodes. I would like to acquire a lock on the cluster to perform some write operations and then release the lock.

From what I've read is - To connect to a cluster we generally connect to one node in the cluster and perform all operations on that node which in-turn handles re-directing to other nodes in the cluster.

Is it possible to acquire lock on a Redis cluster? [P.S I am using Redisson client] From the examples in Redisson client under Multilock and redlock (https://github.com/redisson/redisson/wiki/8.-Distributed-locks-and-synchronizers), they are acquiring a lock on individual nodes.

• How does Multi lock or Red lock work on a cluster?
• How and what kind of lock do I use if I have a Redis cluster?
• Which library (Jedis/Redisson) do I use?

Jedis also seems to have support for locking on the cluster (https://github.com/kaidul/jedis-lock).

P.S: I've read extensively on this, but I've not been able to find clear answers on locking on a cluster. Would really appreciate some help.

I'm having trouble adding a Compliance Standard to an existing Policy via the Pal Alto Prisma Cloud API.

Everytime I send the request, I'm returned with a 500 Server Error (and, unfortunately, the API documentation is super unhelpful with this). I'm not sure if I'm sending the right information to add a compliance standard as the API documentation doesn't show what info needs to be sent. If I leave out required fields (name, policyType, and severity), I'm returned a 400 error (bad request, which makes sense). But I can't figure out why I keep getting the 500 Server Error.

In essence, my code looks like:

I need to connect to a single Redis instance from an application client.

Since the client will be replicated in Kubernetes, I'm studying Redis documentation about locks to prevent races between the client replicas.

After some googling and reading around, I zeroed in on these two resources:

• the SETNX command described here: https://redis.io/commands/setnx
• the Redlock algorithm described here: https://redis.io/topics/distlock

Interestingly the SETNX docs explicitly advise against using SETNX to implement locks, stating that it has basically become obsolete:

The following pattern is discouraged in favor of the Redlock algorithm [...]

We document the old pattern anyway because certain existing implementations link to this page as a reference.

However the Redlock algorithm is specifically tailored for distributed locks, thus when one seeks to lock on multiple Redis instances - they actually refer to multiple masters.

To go a bit further, the library redsync (golang) declares the New function as follows:

How to make the images painted in canvas valid for all screen sizes? my code but it doesn't work, the painted game screen is too large for small screens and too small for large screens, I have tried everything and nothing works still, I want the canvas to scale according to the screen's size

this is the result I get and the desired result: https://imgur.com/a/bSnGfov

Here's my code for the game canvas:

So I just read about redlock. What I understood is that it needs 3 independent machines to work. By independent they mean that all the machines are masters and there is no replication amongst them, which means they are serving different types of data. So why would I need to lock a key present in three independent redis instances acting as masters ? What are the use cases where I would need to use redlock ?