Allow user input during loop execution for macOS - objective-c

Question

I have an Objective C MacOS project In Xcode 12.3 with a loop containing code that writes to user interface controls and may display alerts. When the loop runs, the cursor becomes a rotating rainbow disc. Clicking on a toolbar item (or any user interface control) has no effect until the loop has terminated.
I would like to have a toolbar item accept user clicks during loop execution. Whilst running the loop in a separate thread would allow this, substantial recoding would be required to remove the interface references and alerts from the loop code.
Is there a way of pausing the loop execution to check for input from user controls such as toolbar items? Adding [[NSRunloop mainRunLoop] runUntilDate:[NSDate datewithTimeIntervalSinceNow:0.5]];at the start of the loop code does not achieve this.
I've tried running the loop code (runBatch) in a separate thread using
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul);
dispatch_async(queue, ^{
[self runBatch];
dispatch_sync(dispatch_get_main_queue(), ^{
});
});
The loop code is contained in runBatch, which sets and reads various UI controls and these are are flagged as only being accessible from the main thread at run time. The project builds OK. Placing these UI interactions on the main thread after async queue completion would be difficult.
An example of code showing the problem is below. The project consists of a window with an NSTextField (outlet textData) and three buttons, two of which run a loop and the third (Stop) sets a stop flag. The runMain shows the index in textData, but when it runs only the final value appears and the Stop button is not responsive. The cursor becomes a coloured wheel after about 3 seconds when it is moved off the Start button.
When the loop is run on the background thread, the Stop button is responsive but textData cannot be updated from the background thread.
What I would like is for textData to show the index value while the loop is running.
AppDelegate.h
#import <Cocoa/Cocoa.h>
#interface AppDelegate : NSObject <NSApplicationDelegate>
#property (weak) IBOutlet NSTextField *textData;
#end
AppDelegate.m
#import "AppDelegate.h"
#interface AppDelegate ()
#property (strong) IBOutlet NSWindow *window;
#end
#implementation AppDelegate
#synthesize textData;
static bool stopBatch = false;
- (IBAction)runMain:(id)sender {
stopBatch = false;
[self runMain];
}
- (IBAction)stopClick:(id)sender {
stopBatch = true;
}
- (IBAction)runBackground:(id)sender {
stopBatch = false;
[self runBatchBackground];
}
-(void) runMain{
[textData setStringValue:#"Start"];
[textData displayIfNeeded];
NSString * iString = #"0";
for (int i=0;i<=10000 ;i++)
{
iString= [NSString stringWithFormat: #"%d",i];
[textData setStringValue:iString];
[textData displayIfNeeded];
if(stopBatch)
{
break;
}
}
NSString *iStringFinal = iString;
}
-(void)runBatchBackground{
[textData setStringValue:#""];
NSString * __block iString = #"0";
dispatch_queue_t backgroundQueue = dispatch_queue_create("Network",nil);
dispatch_async(backgroundQueue, ^(void){
for (int i=0;i<=10000000 ;i++)
{
iString= [NSString stringWithFormat: #"%d",i];
//[self->_textData setStringValue:iString];
//[self->_textData displayIfNeeded];
if(stopBatch)
{
break;
}
}
NSString *iStringFinal = iString;
});
}
#end
After some experimentation I found a simpler solution than that kindly provided by #willeke. Using runMain code as shown below, adding a timerCalled method and adding a class variable iVal allowed the Stop button action to be executed while the loop was running. It appears that the 10000 timer requests are queued and then executed without blocking the main loop (and access to user controls) until timerCalled is exited using a return statement as shown. Is there anything wrong with this approach?
-(void) runMain{
for (int i=0;i<10000 ;i++)
{
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(timerCalled) userInfo:nil repeats:NO];
}
}
-(void)timerCalled{
if(stopBatch) return;
for (int i=0;i<10;i++)
{
iVal++;
iString= [NSString stringWithFormat: #"%ld",iVal];
[textData setStringValue:iString];
}
}

Answer 1

Here you go
- (void)runBatchBackground {
[self.textData setStringValue:#""];
NSString * __block iString = #"0";
dispatch_queue_t backgroundQueue = dispatch_queue_create("Network",nil);
dispatch_async(backgroundQueue, ^(void){
for (int i = 0; i <= 10000000; i++)
{
// Simulate some processing
// If the code on the background thread runs faster than the code
// on the main thread, then the main thread is lagging behind and doesn't
// have time to process events.
[NSThread sleepForTimeInterval:0.25];
iString = [NSString stringWithFormat: #"%d",i];
// Execute UI code on the main thread.
dispatch_async(dispatch_get_main_queue(), ^{
[self.textData setStringValue:iString];
//[self.textData displayIfNeeded]; displayIfNeeded is not needed
});
if (self->stopBatch)
{
break;
}
}
});
}