dispatch_group_t - EXC_BAD_INSTRUCTION

Question

这是我第一次使用 dispatch_group_t，我犯了一个简单的错误。 dispatch_group_notify 在任何异步调用返回之前被调用，因此甚至在第一个 dispatch_group_leave(group) 之前被调用，然后抛出 EXC_BAD_INSTRUCTION。

但是，我不知道为什么会这样。

dispatch_queue_t queue =      dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();

dispatch_group_async(group, queue, ^{
    [self getCategoriesMainWithParameters:nil withSuccess:^(NSArray *objects) {
        [categoriesMain addObjectsFromArray:objects];
        dispatch_group_leave(group);
    } failure:^(NSError *error) {
        groupError = error;
        dispatch_group_leave(group);
    }];
});

dispatch_group_async(group, queue, ^{
    [self getCategoriesSubWithParameters:nil withSuccess:^(NSArray *objects) {
        [categoriesSub addObjectsFromArray:objects];
        dispatch_group_leave(group);
    } failure:^(NSError *error) {
        groupError = error;
        dispatch_group_leave(group);
    }];
});

dispatch_group_async(group, queue, ^{
    [self getCategoriesProductWithParameters:nil withSuccess:^(NSArray *objects) {
        [categoriesProduct addObjectsFromArray:objects];
        dispatch_group_leave(group);
    } failure:^(NSError *error) {
        groupError = error;
        dispatch_group_leave(group);
    }];
});

dispatch_group_notify(group,dispatch_get_main_queue(),^{
   ...
});

Answer 1

函数dispatch_group_async在调度块时自动“进入”组，并在调度块完成时自动“离开”。但是你再次调用 dispatch_group_leave，所以你最终调用了太多的“离开”，导致你描述的错误。

应该调用 dispatch_group_async（为您进行所有“进入”和“离开”调用），或者在异步调用之前手动调用 dispatch_group_enter 并调用 dispatch_group_leave在异步进程的完成处理程序中。

在这种情况下，因为您在调度块中调用异步任务，所以 dispatch_group_async 模式将不起作用。您希望在调用异步方法之前手动 dispatch_group_enter，然后让完成处理程序调用 dispatch_group_leave，正如您所做的那样。当每个“进入”都与“离开”相匹配时，该组将收到通知。而且因为您调用的方法已经是异步的，所以您根本不需要使用 dispatch_async 或 dispatch_group_async。

因此，它可能看起来像：

dispatch_group_t group = dispatch_group_create();

dispatch_group_enter(group);
[self getCategoriesMainWithParameters:nil withSuccess:^(NSArray *objects) {
    [categoriesMain addObjectsFromArray:objects];
    dispatch_group_leave(group);
} failure:^(NSError *error) {
    groupError = error;
    dispatch_group_leave(group);
}];

dispatch_group_enter(group);
[self getCategoriesSubWithParameters:nil withSuccess:^(NSArray *objects) {
    [categoriesSub addObjectsFromArray:objects];
    dispatch_group_leave(group);
} failure:^(NSError *error) {
    groupError = error;
    dispatch_group_leave(group);
}];

dispatch_group_enter(group);
[self getCategoriesProductWithParameters:nil withSuccess:^(NSArray *objects) {
    [categoriesProduct addObjectsFromArray:objects];
    dispatch_group_leave(group);
} failure:^(NSError *error) {
    groupError = error;
    dispatch_group_leave(group);
}];

dispatch_group_notify(group,dispatch_get_main_queue(),^{
    ...
});

dispatch_group_t - EXC_BAD_INSTRUCTION

dispatch_group_t - EXC_BAD_INSTRUCTION

objective-c

grand-central-dispatch