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Allow native modules to customize the main-thread init behaviour

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Summary:
We've simplified a lot of the conditions for eager of the module init so now we can introduce a final switch to allow modules to opt-out (and in the future opt-in if they still require the behaviour).

We now require you to be explicit about the intended behaviour and implement the `+ (BOOL)requiresMainQueueSetup` method on your module. When you return YES from this method, it tells the bridge the module needs to be created on the main thread (and to avoid deadlocks, we do so eagerly during bridge startup). When you return NO, the native module will be initialised when it's first accessed from JS.

The current behaviour is maintained but a warning is emitted until the new API is adopted.

Reviewed By: fkgozali

Differential Revision: D5527788

fbshipit-source-id: 56d38f81e58cf950547b9780e89bfac4667eeaaa
This commit is contained in:
Pieter De Baets
2017-08-07 06:45:23 -07:00
committed by Facebook Github Bot
parent 1cd276ab5c
commit d42ccca2e1
3 changed files with 57 additions and 21 deletions
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46
React/Base/RCTModuleData.mm
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@@ -38,21 +38,37 @@
_implementsBatchDidComplete = [_moduleClass instancesRespondToSelector:@selector(batchDidComplete)];
_implementsPartialBatchDidFlush = [_moduleClass instancesRespondToSelector:@selector(partialBatchDidFlush)];
static IMP objectInitMethod;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
objectInitMethod = [NSObject instanceMethodForSelector:@selector(init)];
});
// If a module overrides `constantsToExport` then we must assume that it
// must be called on the main thread, because it may need to access UIKit.
// If a module overrides `constantsToExport` and doesn't implement `requiresMainQueueSetup`, then we must assume
// that it must be called on the main thread, because it may need to access UIKit.
_hasConstantsToExport = [_moduleClass instancesRespondToSelector:@selector(constantsToExport)];
// If a module overrides `init` then we must assume that it expects to be
// initialized on the main thread, because it may need to access UIKit.
const BOOL hasCustomInit = !_instance && [_moduleClass instanceMethodForSelector:@selector(init)] != objectInitMethod;
const BOOL implementsRequireMainQueueSetup = [_moduleClass respondsToSelector:@selector(requiresMainQueueSetup)];
if (implementsRequireMainQueueSetup) {
_requiresMainQueueSetup = [_moduleClass requiresMainQueueSetup];
} else {
static IMP objectInitMethod;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
objectInitMethod = [NSObject instanceMethodForSelector:@selector(init)];
});
_requiresMainQueueSetup = _hasConstantsToExport || hasCustomInit;
// If a module overrides `init` then we must assume that it expects to be
// initialized on the main thread, because it may need to access UIKit.
const BOOL hasCustomInit = !_instance && [_moduleClass instanceMethodForSelector:@selector(init)] != objectInitMethod;
_requiresMainQueueSetup = _hasConstantsToExport || hasCustomInit;
if (_requiresMainQueueSetup) {
const char *methodName = "";
if (_hasConstantsToExport) {
methodName = "constantsToExport";
} else if (hasCustomInit) {
methodName = "init";
}
RCTLogWarn(@"Module %@ requires main queue setup since it overrides `%s` but doesn't implement "
"`requiresMainQueueSetup. In a future release React Native will default to initializing all native modules "
"on a background thread unless explicitly opted-out of.", _moduleClass, methodName);
}
}
}
- (instancetype)initWithModuleClass:(Class)moduleClass
@@ -291,9 +307,7 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
if (_hasConstantsToExport && !_constantsToExport) {
RCT_PROFILE_BEGIN_EVENT(RCTProfileTagAlways, ([NSString stringWithFormat:@"[RCTModuleData gatherConstants] %@", _moduleClass]), nil);
(void)[self instance];
if (!_requiresMainQueueSetup) {
_constantsToExport = [_instance constantsToExport] ?: @{};
} else {
if (_requiresMainQueueSetup) {
if (!RCTIsMainQueue()) {
RCTLogWarn(@"Required dispatch_sync to load constants for %@. This may lead to deadlocks", _moduleClass);
}
@@ -301,6 +315,8 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
RCTUnsafeExecuteOnMainQueueSync(^{
self->_constantsToExport = [self->_instance constantsToExport] ?: @{};
});
} else {
_constantsToExport = [_instance constantsToExport] ?: @{};
}
RCT_PROFILE_END_EVENT(RCTProfileTagAlways, @"");
}