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Ramanpreet Nara
553729f3d6
Summary: ## Problem: Let `A` be the set of all ObjC NativeModules that neither provide nor reqeust a method queue. The TurboModule system dispatches all method calls to NativeModules in `A` synchronously to the JS thread. Here is the relevant logic: **RCTTurboModule.mm:** Link: https://fburl.com/diffusion/nz9gqje8 ``` jsi::Value performMethodInvocation( // ... ) { // ... dispatch_queue_t methodQueue = NULL; if ([instance_ conformsToProtocol:protocol(RCTBridgeModule)] && [instance_ respondsToSelector:selector(methodQueue)]) { methodQueue = [instance_ performSelector:selector(methodQueue)]; } if (methodQueue == NULL || methodQueue == RCTJSThread) { // This is the default mode of execution: on JS thread. block(); } else if (methodQueue == dispatch_get_main_queue()) { ``` **Why does this end up happening?** 1. NativeModules that request a method queue have `synthesize methodQueue = _methodQueue` in their `implementation` section. This generates a `methodQueue` getter for the NativeModule, and also creates an ivar to back that getter. The TurboModule system generates a `dispatch_queue_t` and uses ObjC's KVC API to write to the ivar. So in the above logic, for NativeModules that provide a method queue, methodQueue will neither be `NULL` nor `RCTJSThread`, so we don't dispatch synchronously to the JS thread. 2. NativeModules that provide a method queue will return something that is not `NULL` or something that is `RCTJSThread`. If they return `NULL`, the infra will throw an error early. If they return `RCTJSThread`, we'll dispatch synchronously to the JS thread, as we should (...wait. For async NativeModule methods that dispatch to `RCTJSThread`, should we dispatch asynchronously to the JS thread, via jsInvoker? **Edit:** Nope: https://fburl.com/diffusion/ivt9b40s.). In all other cases, we dispatch to appropriately to the respective method queue. 3. For NativeModules that neither provide nor request a method queue (i.e: NativeModules in `A`), they don't implement the `methodQueue` selector. Therefore, we dispatch synchronously to the JS thread. ## The fix (Part 1): The first step towards fixing this problem is to generate `dispatch_queue_t`s for NativeModules in `A`. That's what this diff accomplishes. Changelog: [iOS][Fixed] - Create method queue for NativeModules that don't provide nor request one. Reviewed By: fkgozali Differential Revision: D20821054 fbshipit-source-id: 17a73550ad96766c5c7e719e28e1cc879e36465c