003fa7adda
Fundamentally, we should take a write lock on the message, check its validity for a change, and then make and commit that change. Previously, `check_update_message` did not operate in a transaction, but `do_update_message` did -- which led to the ordering: - `check_update_message` reads Message, not in a transaction - `check_update_message` verifies properties of the Message - `do_update_message` starts a transaction - `do_update_message` takes a read lock on UserMessage - `do_update_message` writes on UserMessage - `do_update_message` writes Message - `do_update_message` commits This leads to race conditions, where the `check_update_message` may have verified based on stale data, and `do_update_message` may improperly overwrite it; as well as deadlocks, where other (properly-written) codepaths take a write lock on Message _before_ updating UserMessage, and thus deadlock with `do_update_message`. Change `check_update_message` to open a transaction, and take the write lock when first accessing the Message row. We update the comment above `do_update_message` to clarify this expectation. The new ordering is thus: - `check_update_message` starts a transaction - `check_update_message` takes a write lock on Message - `check_update_message` verifies properties of the Message - `do_update_message` writes on UserMessage - `do_update_message` writes Message - `check_update_message` commits |
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| confirmation | ||
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| CODE_OF_CONDUCT.md | ||
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| LICENSE | ||
| NOTICE | ||
| README.md | ||
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README.md
Zulip overview
Zulip is an open-source team collaboration tool with unique topic-based threading that combines the best of email and chat to make remote work productive and delightful. Fortune 500 companies, leading open source projects, and thousands of other organizations use Zulip every day. Zulip is the only modern team chat app that is designed for both live and asynchronous conversations.
Zulip is built by a distributed community of developers from all around the world, with 74+ people who have each contributed 100+ commits. With over 1000 contributors merging over 500 commits a month, Zulip is the largest and fastest growing open source team chat project.
Come find us on the development community chat!
Getting started
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Contributing code. Check out our guide for new contributors to get started. We have invested in making Zulip’s code highly readable, thoughtfully tested, and easy to modify. Beyond that, we have written an extraordinary 150K words of documentation for Zulip contributors.
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Contributing non-code. Report an issue, translate Zulip into your language, or give us feedback. We'd love to hear from you, whether you've been using Zulip for years, or are just trying it out for the first time.
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Checking Zulip out. The best way to see Zulip in action is to drop by the Zulip community server. We also recommend reading about Zulip's unique approach to organizing conversations.
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Running a Zulip server. Self-host Zulip directly on Ubuntu or Debian Linux, in Docker, or with prebuilt images for Digital Ocean and Render. Learn more about self-hosting Zulip.
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Using Zulip without setting up a server. Learn about Zulip Cloud hosting options. Zulip sponsors free Zulip Cloud Standard for hundreds of worthy organizations, including fellow open-source projects.
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Participating in outreach programs like Google Summer of Code and Outreachy.
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Supporting Zulip. Advocate for your organization to use Zulip, become a sponsor, write a review in the mobile app stores, or help others find Zulip.
You may also be interested in reading our blog, and following us on Twitter and LinkedIn.
Zulip is distributed under the Apache 2.0 license.