Async call causing EXC_BAD_INSTRUCTION crash - ios

Question

The app I'm working on is using a function that is working fine but blocks the main thread. I am attempting to add a loading spinner using SVProgressHUD and that requires I call my function asynchronously in order to display the spinner. As soon as I call the function asynchronously however the app crashes with EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0 The only change I have made to the function is to invoke the popViewControllerAnimated lines on the main thread. Why is running this code on a new thread causing it to crash and how can I fix it?
Calling code:
-(void) _doSaveDataPoint {
[SVProgressHUD show];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self _saveDataPoint];
dispatch_async(dispatch_get_main_queue(), ^{
[SVProgressHUD dismiss];
});
});
}
_saveDataPoint function. popViewController called on main thread near the end of this code:
-(void) _saveDataPoint {
NSString *errorMsg = nil;
if ([[myLegend type] isEqualToString:#"PIN"]) {
if ([myNodes count]==0) {
errorMsg = #"Please make sure you have added one point on to the map to continue.";
}
}
else if ([[myLegend type] isEqualToString:#"POLYGON"]) {
if ([myNodes count]<3) {
errorMsg = #"Please make sure you have at least 3 points set before continuing.";
}
}
else {
if ([myNodes count]<2) {
errorMsg = #"Please make sure you have at least 2 points set before continuing.";
}
}
if (errorMsg !=nil) {
UIAlertController *alertController = [UIAlertController
alertControllerWithTitle:#"Not enough points"
message:errorMsg
preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction *okAction = [UIAlertAction
actionWithTitle:#"OK"
style:UIAlertActionStyleDefault
handler:^(UIAlertAction *action) {
// Just dismiss
}];
[alertController addAction:okAction];
dispatch_async(dispatch_get_main_queue(), ^{
[self presentViewController:alertController animated:YES completion:nil];
});
return;
}
ClientLegendDataPointBounds *bounds = [[ClientLegendDataPointBounds alloc] init];
int count = 0;
GeoPoint *first = nil;
NSMutableDictionary *attr = [[NSMutableDictionary alloc] init];
for (_EditAnnotation *anno in myNodes) {
GeoPoint *point = [[GeoPoint alloc] initWithLatitude:[anno coordinate].latitude andLongitude:[anno coordinate].longitude];
[bounds expand:point];
if (count==0) {
first = point;
count++;
continue;
}
NSString *xKey = [NSString stringWithFormat:#"x%d",count-1];
NSNumber *xCoord = [NSNumber numberWithDouble:[point latitude ]];
NSString *yKey = [NSString stringWithFormat:#"y%d",count-1];
NSNumber *yCoord = [NSNumber numberWithDouble:[point longitude]];
[attr setObject:xCoord forKey:xKey];
[attr setObject:yCoord forKey:yKey];
count++;
}
if (count>0) {
NSString *pointCount = [NSString stringWithFormat:#"%d", count-1];
[attr setObject:pointCount forKey:#"pointCount"];
}
[self _setBarThemeDefault];
if (myDataPoint==nil) {
myDataPoint = [myLegend addDataPoint:[NSNumber numberWithLongLong:[DateTime currentTimeInMillis]] title:#"" description:#"" latitude:[first latitude] longitude:[first longitude] attributes:attr type:[myLegend type] bounds:bounds];
dispatch_async(dispatch_get_main_queue(), ^{
[[self navigationController] popViewControllerAnimated:NO];
});
[myHandler newItemCreated:myDataPoint];
} else {
[myDataPoint setAttributes:attr];
[myDataPoint setBounds:bounds];
[myDataPoint setLatitude:[first latitude]];
[myDataPoint setLongitude:[first longitude]];
[myDataPoint setModified:[NSNumber numberWithLongLong:[DateTime currentTimeInMillis]]];
[myDataPoint update];
dispatch_async(dispatch_get_main_queue(), ^{
[[self navigationController] popViewControllerAnimated:YES];
});
[myHandler itemUpdated:myDataPoint];
}
[self _finishSurveyLog:[SurveyLogItem ACT_SAVE_SPATIAL_CONST]];
[self _saveUserLocation];
}

Answer 1

I don't know exactly the plugin but could it be that the plugin itselfs dispatches the ui stuff to the main queue? So you don't have to dispatch the call to the main queue by yourself. Take a look at the source code:
SVProgressHUD.m