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Improve TreeTypeAdapter thread-safety #1976

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Marcono1234
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@Marcono1234 Marcono1234 commented Sep 24, 2021

Gson claims to be thread-safe so TreeTypeAdapter.delegate() might be called by multiple threads. To guarantee that each thread sees a fully constructed delegate, the field has to be volatile.

Otherwise when a user-defined type adapter with non-final fields (even though it is stateless) is being used as delegate a thread might see an incomplete constructed instance. See Safe Publication and Safe Initialization in Java; the current case of TreeTypeAdapter.delegate() would be similar to the "Unsafe Local DCL & Unsafe Singleton" case shown in that blog post.

Gson claims to be thread-safe so TreeTypeAdapter.delegate() might be
called by multiple threads. To guarantee that each thread sees a fully
constructed `delegate`, the field has to be `volatile`.
@google-cla google-cla bot added the cla: yes label Sep 24, 2021
@eamonnmcmanus eamonnmcmanus merged commit a92bbf8 into google:master Nov 1, 2021
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@Marcono1234 Marcono1234 deleted the marcono1234/TreeTypeAdapter-thread-safety branch Nov 1, 2021
tibor-universe pushed a commit to getuniverse/gson that referenced this pull request Nov 21, 2021
* Improve TreeTypeAdapter thread-safety

Gson claims to be thread-safe so TreeTypeAdapter.delegate() might be
called by multiple threads. To guarantee that each thread sees a fully
constructed `delegate`, the field has to be `volatile`.

* Improve TreeTypeAdapter thread race comment
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