Use RCTBridgeModule's bridge property instead of [RCTBridge currentBridge]

[cltnschlosser]

From the docs of RCTBridge:

/**
 * The last current active bridge instance. This is set automatically whenever
 * the bridge is accessed. It can be useful for static functions or singletons
 * that need to access the bridge for purposes such as logging, but should not
 * be relied upon to return any particular instance, due to race conditions.
 */
+ (instancetype)currentBridge
{
  return RCTCurrentBridgeInstance;
}

What I've found is there exists a race condition where a JS reload triggered very early could potentially result in MMKV install failing in the initial JS context. Much of this is due to the bridge invalidation being asynchronous. It looks something like this:

• App launch
• Bridge 1 is created
• currentBridge set to bridge 1
• Bridge 1 runtime is initialized (start JS)
• *Reload
• Bridge 1 invalidation start
• currentBridge set to nil
• Bridge 2 is created
• currentBridge is set to bridge 2
• *MMKV from bridge 1 calls install (get’s currentBridge from bridge 2)
  Arbitrary order:
• MMKV install error thrown from bridge 1
• Bridge 1 invalidation finishes (JS stops running)
• Bridge 2 runtime is initialized (start JS)

*Very precisely placed steps to trigger this race condition

Realistically we don't care that the MMKV install in bridge 1 failed, except for the fact that it will throw an error (which can crash the app). Using _bridge we have access the correct bridge, even if it's invalidation has started. The install work in the bridge 1 context may be unnecessary and will be later thrown away when the invalidation is finished, but at least it doesn't error. Later MMKV install is called in bridge 2's context and this is what will be used going forward.

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[cltnschlosser]

_bridge is defined on line 15 @synthesize bridge = _bridge; this follows the documentation here https://github.com/facebook/react-native/blob/7c581f3d3007954413d68daf2e868ce93e120615/React/Base/RCTBridgeModule.h#L159

/**
 * A reference to the RCTBridge. Useful for modules that require access
 * to bridge features, such as sending events or making JS calls. This
 * will be set automatically by the bridge when it initializes the module.
 * To implement this in your module, just add `@synthesize bridge = _bridge;`
 * If using Swift, add `@objc var bridge: RCTBridge!` to your module.
 */
@property (nonatomic, weak, readonly) RCTBridge *bridge;

[ammarahm-ed]

Thanks for debugging this and sending a fix! Looks good.