iOS PTTextSearch locks main thread

[Brad Mueller]

Hi, I'm having an issue where, occasionally, my search function is locking the main thread, despite being queued to run on a background. The issue is more prominent on slower devices.

Below is my PTPDFDoc category method for performing search. Included in it is a `OBDPDFSearchRequest` object which I use to allow the caller to cancel a search in progress. I added that so I can cancel & search the document as a user types without needing to hit "Enter". 

Please advise if there is something I'm doing wrong that would cause a main thread lock, thanks!

----

- (OBDPDFSearchRequest *)obd_searchForText:(NSString *)text completion:(void (^)(OBDPDFSearchRequest *request, NSArray<PTSearchResult *> *results))completion

{

    NSParameterAssert(completion);

    

    if (text.length == 0)

    {

        completion(nil, nil);

        return nil;

    }

    

    OBDPDFSearchRequest *request = [[OBDPDFSearchRequest alloc] init];

    request.isActive = YES;

    request.searchString = text;

    request.isCancelled = NO;

    

    PTTextSearch *textSearch = [[PTTextSearch alloc] init];

    unsigned int mode = e_pthighlight | e_ptambient_string;

    

    __block NSMutableArray <PTSearchResult *> *results = [[NSMutableArray alloc] init];

    

    __weak typeof(self) weakSelf = self;

    

    dispatch_queue_t queue = dispatch_queue_create("com.onboard.pdf.search", DISPATCH_QUEUE_SERIAL);

    dispatch_async(queue, ^{

        

        [weakSelf Lock];

        if (request.isCancelled == NO && [textSearch Begin:weakSelf pattern:text mode:mode start_page:-1 end_page:-1])

        {

            PTSearchResult *result = [textSearch Run];

            [weakSelf Unlock];

            

            while (result.IsFound == YES && request.isCancelled == NO)

            {

                [results addObject:result];

                

                [weakSelf Lock];

                result = [textSearch Run];

                [weakSelf Unlock];

            }

        }

        else

        {

            [weakSelf Unlock];

        }

        

        if (request.isCancelled == YES)

        {

            [results removeAllObjects];

        }

        

        dispatch_async(dispatch_get_main_queue(), ^{

            

            request.isActive = NO;

            

            completion(request, [NSArray arrayWithArray:results]);

        });

    });

    

    return request;

}

[James]

Hi Brad,

What is the main thread blocking on? Because the text search needs to obtain a read lock on the document, if any other thread including the main thread requires a write lock, it will block until the search releases its lock. Does this explain what you're seeing? (Maybe your app auto-saves every x seconds?)

James