Closing Channels in Objective-C

Closing channels is not a direct concept in Objective-C, but we can simulate similar behavior using Grand Central Dispatch (GCD) and dispatch queues. In this example, we’ll use a dispatch queue to communicate work from the main queue to a worker queue. When we have no more jobs for the worker, we’ll signal completion using a semaphore.

#import <Foundation/Foundation.h>
#import <dispatch/dispatch.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        dispatch_queue_t workerQueue = dispatch_queue_create("com.example.workerQueue", DISPATCH_QUEUE_SERIAL);
        dispatch_semaphore_t doneSemaphore = dispatch_semaphore_create(0);
        
        __block BOOL isWorkComplete = NO;
        
        // Here's the worker block. It repeatedly checks for jobs until isWorkComplete is set to YES.
        dispatch_async(workerQueue, ^{
            while (!isWorkComplete) {
                dispatch_sync(dispatch_get_main_queue(), ^{
                    if (!isWorkComplete) {
                        NSLog(@"received job %d", arc4random_uniform(100));
                    } else {
                        NSLog(@"received all jobs");
                        dispatch_semaphore_signal(doneSemaphore);
                    }
                });
                [NSThread sleepForTimeInterval:0.5]; // Simulate some work
            }
        });
        
        // This sends 3 jobs to the worker over the main queue
        for (int j = 1; j <= 3; j++) {
            NSLog(@"sent job %d", j);
            [NSThread sleepForTimeInterval:0.5]; // Simulate sending delay
        }
        
        NSLog(@"sent all jobs");
        isWorkComplete = YES;
        
        // We await the worker using the semaphore
        dispatch_semaphore_wait(doneSemaphore, DISPATCH_TIME_FOREVER);
        
        NSLog(@"work completed");
    }
    return 0;
}

In this Objective-C version:

We use a dispatch queue (workerQueue) to simulate the worker goroutine.
A semaphore (doneSemaphore) is used to signal when all work is complete.
The isWorkComplete flag is used to indicate when all jobs have been sent.
The worker block continuously checks for jobs until isWorkComplete is set to YES.
We simulate sending jobs by logging messages in a loop.
After sending all jobs, we set isWorkComplete to YES and wait on the semaphore.

To run the program, save it as ClosingChannels.m and compile it with:

$ clang -framework Foundation ClosingChannels.m -o ClosingChannels
$ ./ClosingChannels
sent job 1
received job 42
sent job 2
received job 13
sent job 3
received job 87
sent all jobs
received all jobs
work completed

Note that the exact numbers in “received job” messages will vary due to the use of arc4random_uniform().

While this example doesn’t directly close a channel as in the original code, it demonstrates a similar concept of signaling completion of work in Objective-C using GCD and semaphores.

Non Blocking Channel Operations in Objective-C

Range Over Channels in Objective-C

Learn X By Example

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Closing Channels in Objective-C