How to wait NSTask to finish in async block

Question

 NSURLSessionDataTask *dataTask = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
        if (error)
        {
            NSLog(@"Did fail with error %@" , [error localizedDescription]);
            fail();
            return ;
        }
        else
        {
        }

I use dataTaskWithRequest to send async http request and in the completion block, i want to run a python script.

 NSTask * task = [[NSTask alloc] init];
    [task setLaunchPath:kPythonPath];
    [task setArguments:@[self.scriptFileFullPath,outputFile]];
    [task launch];
    [task waitUntilExit];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(checkPythonTaskStatus:) name:NSTaskDidTerminateNotification object:task];

the python task may take a long time so i should wait for its completion. But the NSTaskDidTerminateNotification will not be sent since the NSTask is running in a separate thread. Anyone know how to wait for NSTask to finish in this condition?

Answer 1

NSTask has a property terminationHandler.

The completion block is invoked when the task has completed. The task object is passed to the block to allow access to the task parameters, for example to determine if the task completed successfully.

---

NSTask * task = [[NSTask alloc] init];
task.launchPath = kPythonPath;
task.arguments = @[self.scriptFileFullPath, outputFile];
task.terminationHandler = ^(NSTask *task){
 // do things after completion
};
[task launch];