For example:
- (void)someFunc {
[self someFunc1];
[self someFunc2];
[self someFunc3];
}
I call someFunc. As I understand if I interrupt the application then the application doesn't guarantee that all the inner code in someFunc will be performed.
I must call someFunc1, someFunc2 and someFunc3 only once.
The problems I don't know how to solve:
someFunc1, someFunc2 and someFunc3 should be called atomically.
storing info for next launch. For example if we successfully have performed someFunc1 only then at next launch the application should call someFunc2 and someFunc3 only.
I know about method applicationWillTerminate:, but I don't know how to solve the current issue with it.
EDITED
Multitasking is not a solution because Even if the device is running iOS 4 or later, the device may not support multitasking., so it doesn't solve the general problem and makes the final solution more difficult only.
EDITED
For those who spam with off topic answers: read the title first - Save state when user exits an application. Where have you seen here putting the application into background?
This does't make sense. If these functions are running on the main thread, there is no way that the application can terminate normally while your functions are running. This is because the events sent like applicationWillTerminate: are sent on the same thread.
If your function is running on a different thread to the main thread, you will need to save some state information after each function completes, but you still have a race condition.
It might be better to check your application's state before running each function. For example, if you have a three step login/registration process with a server, you should query the server to see if the stage has been completed already before running it.
It's difficult to be more specific without knowing what you are doing in these functions.
You should use background tasks !
Take a look at the documentation here :
Executing a Finite-Length Task in the Background
Put the call of someFunc in the middle of the background task.
If your app goes to the background state, you'll have extra time to finish the execution of the method.
Make your functions to return bool, and when you call them, store the bool value to nsdefaults.
When the app restarts,check the bools from sndefaults, and if they are NO, run the functions and update them.
Nobody wants to help. So my temporary solution:
to save a last state I use a writing to a file because it enables to set its operation as atomic/nonatomic
I have replaced this code with something like this:
typedef enum {
state1,
state2,
state3
} MyState;
#property (assign) MyState state;
-(void)someFunc {
switch (state) {
case state1:
{
[self someFunc1];
state = state2;
[self someFunc];
break;
}
case state2:
{
[self someFunc2];
state = state3;
[self someFunc];
break;
}
default:
break;
}
}
Related
I am working on an iOS application that, say on a button click, launches several threads, each executing a piece of Open GL code. These threads either have a different EAGLContext set on them, or if they use same EAGLContext, then they are synchronised (i.e. 2 threads don't set same EAGLContext in parallel).
Now suppose the app goes into background. As per Apple's documentation, we should stop all the OpenGL calls in applicationWillResignActive: callback so that by the time applicationDidEnterBackground: is called, no further GL calls are made.
I am using dispatch_queues to create background threads. For e.g.:
__block Byte* renderedData; // some memory already allocated
dispatch_sync(glProcessingQueue, ^{
[EAGLContext setCurrentContext:_eaglContext];
glViewPort(...)
glBindFramebuffer(...)
glClear(...)
glDrawArrays(...)
glReadPixels(...) // read in renderedData
}
use renderedData for something else
My question is - how to handle applicationWillResignActive: so that any such background GL calls can be not just stopped, but also be able to resume on applicationDidBecomeActive:? Should I wait for currently running blocks to finish before returning from applicationWillResignActive:? Or should I just suspend glProcessingQueue and return?
I have also read that similar is the case when app is interrupted in other ways, like displaying an alert, a phone call, etc.
I can have multiple such threads at any point of time, invoked by possibly multiple ViewControllers, so I am looking for some scalable solution or design pattern.
The way I see it you need to either pause a thread or kill it.
If you kill it you need to ensure all resources are released which means again calling openGL most likely. In this case it might actually be better to simply wait for the block to finish execution. This means the block must not take too long to finish which is impossible to guarantee and since you have multiple contexts and threads this may realistically present an issue.
So pausing seems better. I am not sure if there is a direct API to pause a thread but you can make it wait. Maybe a s system similar to this one can help.
The linked example seems to handle exactly what you would want; it already checks the current thread and locks that one. I guess you could pack that into some tool as a static method or a C function and wherever you are confident you can pause the thread you would simply do something like:
dispatch_sync(glProcessingQueue, ^{
[EAGLContext setCurrentContext:_eaglContext];
[ThreadManager pauseCurrentThreadIfNeeded];
glViewPort(...)
glBindFramebuffer(...)
[ThreadManager pauseCurrentThreadIfNeeded];
glClear(...)
glDrawArrays(...)
glReadPixels(...) // read in renderedData
[ThreadManager pauseCurrentThreadIfNeeded];
}
You might still have an issue with main thread if it is used. You might want to skip pause on that one otherwise your system may simply never wake up again (not sure though, try it).
So now you are look at interface of your ThreadManager to be something like:
+ (void)pause {
__threadsPaused = YES;
}
+ (void)resume {
__threadsPaused = NO;
}
+ (void)pauseCurrentThreadIfNeeded {
if(__threadsPaused) {
// TODO: insert code for locking until __threadsPaused becomes false
}
}
Let us know what you find out.
In objective C,
I am making my program to wait using while loop
doInitialize()
{
dispach_group_t loadDataGroup=dispatch_group_create();
dispatch_group_async(loadDataGroup,...get_global_queue(..),0),^{
renewauth();
}
dispatch_group_notify(loadDataGroup,...get_global_queue(..),0),^{
//Do other tasks once renew session has completed...
}
}
renewauth()
{
RenewAuthTokenInProgress=true;
startRenewThread();
**while (RenewAuthTokenInProgress);**
}
In turn startRenewThread() function also performs dispatch_async operation inside. So I have to make renewAuth() wait.
And async task in startRenewThread will update the bool variable once renewal is successful.
Is there any better approach of doing it other than dispatch_groups?
And is it good to make other threads wait with while (true) statement?
Manoj Kumar,
using a while loop to wait till the boolean variable change is not the correct approach to solve the problem. Here are few of the issues with this method
Your CPU is un-necessarily burdened with checking the variable regularly.
This will clearly show that developer isn't much equipted with basic skills of coding and features available with language.
If for any reason your variable will never change then your CPU will never stop checking the value of bool in while loop and blocks the execution of further code on the same thread.
Here are few of the correct approach :
Blocks or closures : Make use of blocks to execute the code asynchronously when the RenewAuthToken is done.
Delegates : if blocks are harder to understand, Make use of delegates and trigger the delegate when you are done with RenewAuthToken.
Notifications : Add observer for notifications in classes which needs to respond when RenewAuthToken is done and throw notification from the asynctask and let the class to catch it execute the code.
Locks : If it is necessary to block the execution of the thread till the response comes use locks to control the thread execution rather than using while loop
EDIT
As pointed out by fogmeister in comments
If you block the main thread for too long with a while(true) loop then
the app will actually be terminated by the iOS Watchdog as it will
assume it has crashed
Please have a look at the link : understand iOS watchdog termination reasons provided by fogmeister
Hope it helps.
I believe what you need it's a semaphore like:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
dispatch_semaphore_t sem = dispatch_semaphore_create(0);
__block BOOL done = FALSE;
while (true) {
[self someCompletionMethod completion:^(BOOL success) {
if(success) { // Stop condition
done = TRUE;
}
// do something
dispatch_semaphore_signal(sem); // This will let a new iteration
}];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
if(done) {
dispatch_async(dispatch_get_main_queue(), ^{
// Dispatch to main
NSLog(#"Done!");
break;
});
}
}
});
Semaphores are an old-school threading concept introduced to the world by the ever-so-humble Edsger W. Dijkstra. Semaphores are a complex topic because they build upon the intricacies of operating system functions.
You can see a tutorial here about semaphore and check it out more links: https://www.raywenderlich.com/63338/grand-central-dispatch-in-depth-part-2
I hope this can help you.
What you do is absolutely lethal. It blocks the running thread (presumably the main thread) so the UI is frozen. It runs one core at 100% load for no reason whatsoever which empties the battery rapidly and heats up the phone. This will get you some very, very unhappy customers or very, very happy ex-customers.
Anything like this has to run in the background: startRenewThread should trigger some action that sets RenewAuthTokenInProgress = NO and sets whether there is a new token or not, and then triggers further action.
This is an absolutely essential programming pattern on iOS (and Android as far as I know).
I have a view with a bunch of UISwitch.
My problem is that when I tap on a switch I need to wait about 10 seconds before being able to tap any other switch of the view.
Here is my code :
-(void) didTapSwitch:(UISwitch *)sender
{
NSLog(#"BEGIN didTapSwitch, %#",sender);
DADudesManager *dudesManager = [DADudesManager getInstance];
DADude *updatedDude = [dudesManager.dudesList objectAtIndex:[[self.spendingDudesTableView indexPathForCell:sender.superview.superview] row]];
DAAccountManager *accountManager = [DAAccountManager getInstance];
[accountManager.accountsOperationQueue addOperationWithBlock:^{
NSLog(#"BACKGROUND OPERATION BEGINS switchDudeBeneficiates, %#",sender);
DASpendingsManager *spendingsManager = [DASpendingsManager getInstance];
[[spendingsManager.spendingObserver childByAppendingPath:self.spending.spendingID] updateChildValues:#{updatedDude.dudeName: [sender isOn] ? #"1" : #"0"}];
NSLog(#"BACKGROUND OPERATION ENDS switchDudeBeneficiates, %#",sender);
}];
NSLog(#"END switchDudeBeneficiates, %#",sender);
}
My spendingObserver is a Firebase object initiated before.
When the code above is executed, the NSLogs show almost instantaneously in the console, the data is updated online at the same time, but the switches don't react to any tap for another 9 to 11 secs.
Of course commenting the line [[spendingsManager.spendingObserver childByAppendingPath:self.spending.spendingID] updateChildValues:#{weakDude.dudeName: [weakSwitch isOn] ? #"1" : #"0"}]; removes the latency, so the problem must come from Firebase, but I have no clue what's going on.
I am probably missing something obvious as I'm pretty new to IOS development !
I can think couple of reasons.
You are sending the PayLoad in the main thread, which is causing the User INterface events to be suspended.
The code you ran, might be linked to other functions in the library you are using, that might be causing the lag.
TRY - >
try putting your code in an NSOperation and execute that. Or use GCD to do work on different thread just not the UI thread which is the main thead.
Step back and simplify. Make your switch code simply log the change in value. NSLog includes a timestamp, so you can tell when the switch events occur.
If do-nothing code responds quickly, as I suspect it will, then add log statements at the beginning and end of your switch action method. That way you can see if there is a delay between the beginning and end of the processing.
You could also run the app in instruments (time profiler) and see where your app is spending time.
I've just read the following post and have tried to implement the approach described there:
Writing iOS acceptance tests using Kiwi - Being Agile
All the stuff described there does work perfectly. But! there is one thing that breaks determinism when I am running my acceptance tests.
Here is the repo on Github where author of the post pushed his experiments (it can be found on the bottom of the page in the comments): https://github.com/moredip/2012-Olympics-iOS--iPad-and-iPhone--source-code/tree/kiwi-acceptance-mk1
Consider this code he uses for tapping a view:
- (void) tapViewViaSelector:(NSString *)viewSelector{
[UIAutomationBridge tapView:[self viewViaSelector:viewSelector]];
sleepFor(0.1); //ugh
}
...where sleepFor has the following definition behind itself:
#define sleepFor(interval) (CFRunLoopRunInMode(kCFRunLoopDefaultMode, interval, false))
It is a naive attempt ('naive' is not about the author, but about the fact that it is the first thing that comes into a head) to wait for a tiny period of time until all the animations are processed and soak all the possible events that were(or could be) scheduled to a main run loop (see also this comment).
The problem is that this naive code does not work in a deterministic way. There are a bunches of UI interactions which cause fx next button tap to be pressed before the current edited textfield's keyboard is disappeared and so on...
If I just increase the time from 0.1 to fx 1 all the problems disappear, but this leads to that every single interaction like "fill in textfield with a text..." or "tap button with title..." become to cost One second!
So I don't mean just increasing a wait time here, but rather a way to make such artificial waits guarantee that I do can proceed my test case with a next step.
I hope that it should be a more reliable way to wait enough until all the stuff caused by current action (all the transitions/animations or whatever main run loop stuff) are done.
To summarize it all to be a question:
Is there a way to exhaust/drain/soak all the stuff scheduled to a main thread and its run loop to be sure that main thread is idle and its run loop is "empty"?
This was my initial solution:
// DON'T like it
static inline void runLoopIfNeeded() {
// https://developer.apple.com/library/mac/#documentation/CoreFOundation/Reference/CFRunLoopRef/Reference/reference.html
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource);
// DON'T like it
if (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource) runLoopIfNeeded();
}
you can try this
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0, true) == kCFRunLoopRunHandledSource);
this will run until no more things in the run loop. you can try to change the time interval to 0.1 if 0 is not working.
To check on the status of a run loop associated with a thread and register callbacks for separate phases, you may use a CFRunLoopObserverRef. This allows for extremely fine grained control over when the callbacks are invoked. Also, you don't have to depend on hacky timeouts and such.
One can be added like so (notice I am adding one to the main run loop)
CFRunLoopObserverRef obs = CFRunLoopObserverCreateWithHandler(kCFAllocatorDefault, kCFRunLoopAllActivities, true, 0 /* order */, handler);
CFRunLoopAddObserver([NSRunLoop mainRunLoop].getCFRunLoop, obs, kCFRunLoopCommonModes);
CFRelease(obs);
Depending on the activities you register for, your handler will get invoked appropriately. In the sample above, the observer listens for all activities. You probably only need kCFRunLoopBeforeWaiting
You handler could look like this
id handler = ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
switch (activity) {
case kCFRunLoopEntry:
// About to enter the processing loop. Happens
// once per `CFRunLoopRun` or `CFRunLoopRunInMode` call
break;
case kCFRunLoopBeforeTimers:
case kCFRunLoopBeforeSources:
// Happens before timers or sources are about to be handled
break;
case kCFRunLoopBeforeWaiting:
// All timers and sources are handled and loop is about to go
// to sleep. This is most likely what you are looking for :)
break;
case kCFRunLoopAfterWaiting:
// About to process a timer or source
break;
case kCFRunLoopExit:
// The `CFRunLoopRun` or `CFRunLoopRunInMode` call is about to
// return
break;
}
};
Here is my current solution, I will add some comments and explanations to the code a bit later, if nobody tell me I am wrong or suggests a better answer first:
// It is much better, than it was, but still unsure
static inline void runLoopIfNeeded() {
// https://developer.apple.com/library/mac/#documentation/CoreFOundation/Reference/CFRunLoopRef/Reference/reference.html
__block BOOL flag = NO;
// http://stackoverflow.com/questions/7356820/specify-to-call-someting-when-main-thread-is-idle
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
dispatch_async(dispatch_get_main_queue(), ^{
flag = YES;
});
});
while (CFRunLoopRunInMode(kCFRunLoopDefaultMode, 0.1, YES) == kCFRunLoopRunHandledSource);
if (flag == NO) runLoopIfNeeded();
}
Right now I don't have any ideas how this could be made more effective.
I use a subclass of NSOperation to upload large files to AWS S3 using Amazon's iOS SDK (v1.3.2). This all works fine, but some beta testers experience deadlocks (iOS 5.1.1). The result is that the NSOperationQueue in which the operations are scheduled is blocked as only one operation is allowed to run at one time. The problem is that I cannot reproduce the issue whereas the beta testers experience this problem every single time.
The operation is quite complex due to how the AWS iOS SDK works. However, the problem is not related to the AWS iOS SDK as far as I know based on my testing. The operation's main method is pasted below. The idea of the operation's main method is based on this Stack Overflow question.
- (void)main {
// Operation Should Terminate
_operationShouldTerminate = NO;
// Notify Delegate
dispatch_async(dispatch_get_main_queue(), ^{
[self.delegate operation:self isPreparingUploadWithUuid:self.uuid];
});
// Increment Network Activity Count
[self incrementNetworkActivityCount];
// Verify S3 Credentials
[self verifyS3Credentials];
while (!_operationShouldTerminate) {
if ([self isCancelled]) {
_operationShouldTerminate = YES;
} else {
// Create Run Loop
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
}
}
// Decrement Network Activity Count
[self decrementNetworkActivityCount];
NSLog(#"Operation Will Terminate");
}
The method that finalizes the multipart upload sets the boolean _operationShouldTerminate to YES to terminate the operation. That method looks like this.
- (void)finalizeMultipartUpload {
// Notify Delegate
dispatch_async(dispatch_get_main_queue(), ^{
[self.delegate operation:self didFinishUploadingUploadWithUuid:self.uuid];
});
// Operation Should Terminate
_operationShouldTerminate = YES;
NSLog(#"Finalize Multipart Upload");
}
The final log statement is printed to the console, but the while loop in the main method does not seem to exit as the final log statement in the operation's main method is not printed to the console. As a result, the operation queue in which the operation is scheduled, is blocked and any scheduled operations are not executed as a result.
The operation's isFinished method simply returns _operationShouldTerminate as seen below.
- (BOOL)isFinished {
return _operationShouldTerminate;
}
It is odd that the while loop is not exited and it is even more odd that it does not happen on any of my own test devices (iPhone 3GS, iPad 1, and iPad 3). Any help or pointers are much appreciated.
The solution to the problem is both complex and simple as it turns out. What I wrongly assumed was that the methods and delegate callbacks of the operation were executed on the same thread, that is, the thread on which the operation's main method was called. This is not always the case.
Even though this was true in my test and on my devices (iPhone 3GS), which is why I did not experience the problem myself. My beta testers, however, used devices with multicore processors (iPhone 4/4S), which caused some of the code to be executed on a thread different from the thread on which the operation's main method was invoked.
The result of this is that _operationShouldTerminate was modified in the finalizeMultipartUpload method on the wrong thread. This in turn means that the while loop of the main method was not exited properly resulting in the operation deadlocking.
In short, the solution is to update _operationShouldTerminate on the same thread as the main method was invoked on. This will properly exit the while loop and exit the operation.
There are a number of problems with your code, and I can offer two solutions:
1) read up on Concurrent NSOperations in Apple's Concurrency Programming Guide. To keep the runLoop "alive" you have to add either a port or schedule a timer. The main loop should contain a autorelease pool as you may not get one (see Memory Management in that same memo). You need to implement KVO to let the operationQueue know when your operation is finished.
2) Or, you can adopt a small amount of field tested hardened code and reuse it. That Xcode project contains three classes of interest to you: a ConcurrentOperation file that does well what you are trying to accomplish above. The Webfetcher.m class shows how to subclass the concurrent operation to perform an asynchronous URL fetch from the web. And the OperationsRunner is a small helper file you can add to any kind of class to manage the operations queue (run, cancel, query, etc). All of the above are less than 100 lines of code, and provide a base for you to get your code working. The OperationsRunner.h file provide a "how to do" too.