Question

在DISPATCH_QUEUE_PRIORITY_DEFAULT gcd队列中运行的dispatch_async块中：我创建了两个RACSubject对象，使用RACSignal merge：然后订阅完成。然后，为了进行此测试（并在我的实际代码中复制场景），我在它们上发送sendComplete。合并的信号完成订阅永远不会触发。我独立地为这些主题附加了两个完成订阅，那些就是开火。如果我在主线程而不是gcd队列上进行相同的测试，那么它会按预期工作。

有没有办法让这项工作或者我将不得不重构以使所有主题都在主线程上？

#import <ReactiveCocoa/ReactiveCocoa.h>

@interface rac_signal_testTests: SenTestCase
@end

@implementation rac_signal_testTests

- (void)setUp
{
    [super setUp];

    // Set-up code here.
}

- (void)tearDown
{
    // Tear-down code here.

    [super tearDown];
}

-(void)test_merged_subjects_will_complete_on_main_thread{
    RACSubject *subject1 = [[RACSubject subject] setNameWithFormat:@"subject1"];
    RACSubject *subject2 = [[RACSubject subject] setNameWithFormat:@"subject2"];

    RACSignal *merged = [RACSignal merge:@[subject1, subject2]];

    __block BOOL completed_fired = NO;

    [merged subscribeCompleted:^{
        completed_fired = YES;
    }];

    [subject1 sendNext:@"1"];
    [subject2 sendNext:@"2"];

    [subject1 sendCompleted];
    [subject2 sendCompleted];

    STAssertTrue(completed_fired, nil);
}

//test proving that throttling isn't breaking the merged signal (initial hypothesis).
-(void)test_merged_subjects_will_complete_if_one_of_them_has_a_throttled_subscriber_on_main_thread{
    RACSubject *subject1 = [[RACSubject subject] setNameWithFormat:@"subject1"];
    RACSubject *subject2 = [[RACSubject subject] setNameWithFormat:@"subject2"];

    __block NSString * hit_subject2_next = nil;
    [[subject2 throttle:.5] subscribeNext:^(NSString *value){
        hit_subject2_next = value;
    }];

    RACSignal *merged = [RACSignal merge:@[subject1, subject2]];

    __block BOOL completed_fired = NO;

    [merged subscribeCompleted:^{
        completed_fired = YES;
    }];

    [subject2 sendNext:@"2"];
    [subject2 sendCompleted];
    [subject1 sendCompleted];
    STAssertEqualObjects(@"2", hit_subject2_next, nil);
    STAssertTrue(completed_fired, nil);
}

-(void)test_merged_subjects_will_complete_if_on_gcd_queue{
    __block BOOL complete = NO;

    dispatch_queue_t global_default_queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

    dispatch_async(global_default_queue, ^{
        RACSubject *subject1 = [[RACSubject subject] setNameWithFormat:@"subject1"];
        RACSubject *subject2 = [[RACSubject subject] setNameWithFormat:@"subject2"];

        __block NSString * hit_subject2_next = nil;

        RACScheduler *global_default_scheduler = [RACScheduler schedulerWithQueue:global_default_queue name:@"com.test.global_default"];

        RACSignal *sig1 = [subject1 deliverOn:RACScheduler.mainThreadScheduler];
        RACSignal *sig2 = [subject2 deliverOn:RACScheduler.mainThreadScheduler];

        [sig2    subscribeNext:^(NSString *value){
            hit_subject2_next = value;
        }];

        [sig2 subscribeCompleted:^{
            NSLog(@"hit sig2 complete");
        }];

        [sig1 subscribeCompleted:^{
            NSLog(@"hit sig1 complete");
        }];

        RACSignal *merged = [[RACSignal merge:@[sig1, sig2]] deliverOn:RACScheduler.mainThreadScheduler];

        [merged subscribeCompleted:^{
            complete = YES;
        }];

        [subject2 sendNext:@"2"];
//        if we dispatch the send complete calls to the main queue then this code works but that seems like it shoul be unnecessary.
//        dispatch_async(dispatch_get_main_queue(), ^{
            [subject1 sendCompleted];
            [subject2 sendCompleted];
//        });
    });

    NSDate *startTime = NSDate.date;
    do{
        [NSRunLoop.mainRunLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:.5]];
    }while(!complete && [NSDate.date timeIntervalSinceDate:startTime] <= 10.0);

    STAssertTrue(complete, nil);
}

@end

Answer 1

因此，这是一个相当糟糕的案例，由GCD和RAC的互动引起。严格来说，没有错误。但令人惊讶和奇怪。我们在https://github.com/ReactiveCocoa/ReactiveCocoa/blob/1bd47736f306befab64859602dbdea18f7f9a3f6/Documentation/DesignGuidelines.md#subscription-will-always-occur-on-a-scheduler的设计指南中讨论了这一要求。

关键是订阅必须始终在已知的调度程序上进行。这是RAC内部强制执行的要求。如果您只使用普通的旧GCD，则没有已知的调度程序，因此RAC必须异步将订阅发送到调度程序。

所以去参加考试：

[merged subscribeCompleted:^{
    complete = YES;
}];

实际订阅是异步发生的，因为没有已知的调度程序。订阅最终会在<{strong> -sendCompleted来电之后发生，并且完全错过了它们。这真的是一种竞争条件，但实际上你可能永远不会看到它成功。

如果可能，修复方法是使用RACScheduler代替GCD。如果需要使用特定的GCD队列，可以使用RACTargetQueueScheduler。例如，您的测试的工作简化版本：

-(void)test_merged_subjects_will_complete_if_on_gcd_queue{ __block BOOL complete = NO; dispatch_queue_t global_default_queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); RACScheduler *scheduler = [[RACTargetQueueScheduler alloc] initWithName:@"testScheduler" targetQueue:global_default_queue]; [scheduler schedule:^{ RACSubject *subject1 = [[RACSubject subject] setNameWithFormat:@"subject1"]; RACSubject *subject2 = [[RACSubject subject] setNameWithFormat:@"subject2"]; RACSignal *merged = [RACSignal merge:@[subject1, subject2]]; [merged subscribeCompleted:^{ complete = YES; }]; [subject1 sendCompleted]; [subject2 sendCompleted]; }]; NSDate *startTime = NSDate.date; do{ [NSRunLoop.mainRunLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate dateWithTimeIntervalSinceNow:.5]]; }while(!complete && [NSDate.date timeIntervalSinceDate:startTime] <= 10.0); STAssertTrue(complete, nil); }

由于订阅是在调度程序中进行的，因此subscribeCompleted:是同步完成的，获取已完成的事件，并且所有内容都符合您的预期。

如果您不需要使用特定的GCD队列并且只想在非主队列上完成，那么请执行以下操作：

[[RACScheduler scheduler] schedule:^{ RACSubject *subject1 = [[RACSubject subject] setNameWithFormat:@"subject1"]; RACSubject *subject2 = [[RACSubject subject] setNameWithFormat:@"subject2"]; RACSignal *merged = [RACSignal merge:@[subject1, subject2]]; [merged subscribeCompleted:^{ complete = YES; }]; [subject1 sendCompleted]; [subject2 sendCompleted]; }];

我希望澄清你所看到的内容。如果我需要重新说一些话，请告诉我。

在dispatch_queue sendComplete上创建的RACSubject不会使其合并信号

1 个答案: