Add synchronized block to protect against race condition #69
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alsutton
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Jan 20, 2021
…nitialized, and when we try to perform .init() which means a race condition can occur (as mentioned in facebook/SoLoader#60). This change uses synchronization on the NativeLoader class, and a secondary check to verify that the initialization needs to take place just before we perform it, in order to reduce the window for a race condition to affect client code. When combined with facebook/SoLoader#69 this will remove the race condition from the code because the initialisation inside SoLoader and inside Fresco will both be synchronized on the NativeLoad.class object.
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Jan 22, 2021
…de (#2579) Summary: Thanks for submitting a PR! Please read these instructions carefully: - [X] Explain the **motivation** for making this change. - [X] Provide a **test plan** demonstrating that the code is solid. - [X] Match the **code formatting** of the rest of the codebase. - [X] Target the `master` branch ## Motivation (required) There is a period of time between checking if NativeLoader has been initialized, and when we try to perform `.init()` which means a race condition can occur (as mentioned in facebook/SoLoader#60). This PR provides a mechanism for client code to avoid that race condition. This change uses synchronization on the `NativeLoader` class object, and a secondary check to verify that the initialization needs to take place just before we perform it in order to reduce the window in which a race condition can happen. When combined with facebook/SoLoader#69 this will remove the race condition from the code because the initialisation inside SoLoader and inside Fresco will both be synchronized on the `NativeLoader.class` object. Without that PR in SoLoader this change will still allow fresco clients to synchronize on `NativeLoader.class` in their own code around any areas which may race with this code in fresco. ## Test Plan (required) This code doesn't alter the functionality of fresco, and so existing tests should provide verification that there is no operational impact. ## Next Steps Sign the [CLA][2], if you haven't already. Small pull requests are much easier to review and more likely to get merged. Make sure the PR does only one thing, otherwise please split it. Make sure all **tests pass** on [Circle CI][4]. PRs that break tests are unlikely to be merged. For more info, see the [Contributing guide][4]. [1]: https://medium.com/martinkonicek/what-is-a-test-plan-8bfc840ec171#.y9lcuqqi9 [2]: https://code.facebook.com/cla [3]: http://circleci.com/gh/facebook/fresco [4]: /~https://github.com/facebook/fresco/blob/master/CONTRIBUTING.md Pull Request resolved: #2579 Reviewed By: oprisnik Differential Revision: D25973346 Pulled By: wizh fbshipit-source-id: 10239f7359e45ffc5deddec86d5798a838fc4bc5
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Fixes: #60
As mentioned in issue #60 if the init method is called twice from two different threads it can result in a race condition where both threads receive false for
NativeLoader.isInitialized(), but, whenNativeLoader.init()is run for a second time it throws an exception.Adding a synchronized block here ensures that only one thread will be able to query the initialisation state and trigger the initialisation at a time.