Maybe I let NSOperation to play a wrong role in non-concurrent job. My requirement is , I want to do a lot of async jobs, but I want them to be completed in order. When task1 is finished after the async callback, task2 can be take into work now. And I make all the task a NSOperation. However, NSOperation is used to multiple thread programming most time. Is my choice wrong. But it remind me to think more about the NSOperation in this case, we can't manage manually the isFinished and isExecute in a sync block since the operation have been release in non-concurrent nsoperation,it means i couldnot use the powerful operation queue to automatically manage the task.Any idea?Thanks for your answer..
edit with code :
-(void)main {
[super main];
self.isOperationExcuting = YES;
self.isOperationFinished = NO;
WEAKSELF
[self query:^(NSArray *array, NSError *error) {
//I set my custom property, but it do not cause my NSOperation to be finished
weakSelf.isOperationFinished = YES;
weakSelf.isOperationExcuting = NO;
}];
}
-(void)query:(void (^)(NSArray *array, NSError *error))block {
BmobQuery *query = [BmobQuery queryWithClassName:#"Room"];
[query findObjectsInBackgroundWithBlock:block];
}
-(BOOL)isFinished {
return self.isOperationFinished;
}
- (BOOL)isExecuting {
return self.isOperationExcuting;
}
- (void)start {
[super start];
NSLog(#"start");
}
- (void)cancel {
[super cancel];
NSLog(#"cancel");
}
Just make all added operations serial by setting maxConcurrentOperationCount to 1.
NSOperationQueue* queue = [[ NSOperationQueue alloc ] init];
queue.maxConcurrentOperationCount = 1;
[queue addOperation:operation1];
[queue addOperation:operation2];
[queue addOperation:operation3];
NSOperationQueue
The NSOperationQueue class regulates the execution of a set of
NSOperation objects. After being added to a queue, an operation
remains in that queue until it is explicitly canceled or finishes
executing its task.
Related
Say you have a method that returns information in two separate blocks, like so:
#interface SomeObject : NSObject
- (instancetype)initWithA:(NSString *)aInfo bInfo:(NSString *)bInfo;
#end
- (void)someMethod:(void (^)(NSString *aInfo))firstBlock
secondBlock:(void (^)(NSString *bInfo))secondBlock {
firstBlock(#"a"); secondBlock(#"b");
}
- (void)ourMethod:(void (^)(SomeObject *object))completionBlock {
SomeObject *someObject = [[SomeObject alloc] initWithA:aInfo bInfo:bInfo];
[self someMethod:^(NSString *aInfo) {
//
} secondBlock:^(NSString *bInfo) {
//
}];
completionBlock(someObject);
}
How would you initialize someObject and pass it back when both of the blocks have completed?
Assume that both blocks are executed asynchronously.
I tried fiddling with GCD's dispatch groups to solve this, however, it didn't seem optimal.
Since you need to create your someObject with the values obtained from the two blocks used in the call to someMethod, you need to create someObject after both blocks have been called.
- (void)ourMethod:(void (^)(BOOL initializationComplete))completionBlock {
__block NSString *a = nil;
__block NSString *b = nil;
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
dispatch_group_enter(group);
[self someMethod:^(NSString *aInfo) {
a = aInfo;
dispatch_group_leave(group);
} secondBlock:^(NSString *bInfo) {
b = bInfo;
dispatch_group_leave(group);
}];
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
SomeObject *someObject = [[SomeObject alloc] initWithA:a bInfo:b];
completionBlock(someObject);
});
}
This doesn't block the caller of ourMethod and it ensures the completion block is only called once both blocks are done.
This solution assumes the two blocks are run asynchronously.
You can use a semaphore, but-- in general-- making an asynchronous operation synchronous is a red flag indicating bad design.
Are the two blocks asynchronous in and of themselves? If so, you could have __block BOOL firstDone = NO; and __block BOOL secondDone = NO; and check appropriately to see if it is time to call the completionBlock. Still ugly and you'll want a synchronization primitive in there to ensure you don't hit a race, but that'd work.
If firstBlock() and secondBlock() are synchronous and on the same queue, then just call completionBlock() after the second is done.
Or, alternatively, if they are asynchronous and simultaneously scheduled, toss 'em on an asynchronous queue and then toss a barrier block on the queue that calls the completionBlock.
In my iOS application I am using Core Data.
For table View listing I use NSFetchedResultsController and
Connecting to Remote store I use NSIncrementalStore.
My FetchedResultsController Context is having MainQueue Cuncurrency type.(I couldn't do it with a PrivateQueueCurrencyTYpe).
For resolving Fault, for a many relationship, the executeFetchResultsCall:withContext:error method is executed from my IncrementalStore subclass.
Inside the executeFetchResults method, I will invoke the API (connecting to remote server) if it is not available in my local database.
myarray = [object representationsForRelationship:#"manyconnection" withParams:nil];
Now I need the results array in return synchronously to be returned to the ExecuteFetchResultsMethod. Also this operation should be executed on Main thread.
So I am having only one option to fetch the results from server which causes the UI to unresponsive for the specified sleep time.
-(RequestResult*)makeSyncJsonRequest{
__block RequestResult *retResult = [[RequestResult alloc] init];
__block BOOL block = YES;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
void (^resultBlock)(RequestResult*) = ^(RequestResult* result){
if(!retResult.error)
retResult = result;
block = NO;
dispatch_group_leave(group);
};
// Add a task to the group
dispatch_group_async(group, queue, ^{
// Some asynchronous work
dispatch_group_enter(group);
[self makeAsyncJsonRequestWithBlock:resultBlock];
});
// Do some other work while the tasks execute.
// When you cannot make any more forward progress,
// wait on the group to block the current thread.
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
return retResult;
}
As the above operation is being executed on main thread,the UI hangs.
Inorder to make the UI smoother, I need to carry out the executeFetchrequest in some other thread which is not possible.
It also expects the results array in return.
Is there any option to carry out this something like in a completion handler manner?
or
Any alternate methods or design to work this proper.
Any Help is highly appreciated.
This is a skeleton, using a dispatch_group, assuming you are using an NSFetchedResultsController to update your UITableView:
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// do your setup (FetchedResultsController and such)
[self syncData];
}
- (void)syncData
{
NSArray<Entity*> *results = [self fetchData];
BOOL needsUpdateFromServer = YES; // check your results and set this bool accordingly
if (!needsUpdateFromServer) {
return;
}
__block ServerResponse *fromServer = nil;
__block dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
[self loadDataFromServer:^(ServerResponse *response) {
fromServer = response;
dispatch_group_leave(group);
}];
dispatch_group_notify(group,dispatch_get_main_queue(),^{
[self persistData:fromServer];
/*
According to our discussion, you are using an NSFetchedResultsController.
So your tableView should update automatically after persisting the data.
*/
});
}
- (void)loadDataFromServer:(void (^)(ServerResponse *response))completion
{
// [someDownloadService downloadDataFromServerInBackgroundWithCompletion:^(ServerResponse* response){
dispatch_async(dispatch_get_main_queue(), ^{
completion(response);
});
// }];
}
- (NSArray<Entity*>*)fetchData
{
NSArray<Entity*> *results = nil;
// fetch from core data and return it
return results;
}
- (void)persistData:(NSArray<ServerResponse*> *)serverResponses
{
// parse whatever you get from server
// ... and persist it using Core Data
}
#end
I have created NSOperation class in that class i am calling NSURLConnection to fetch some data.
I am calling NSURLConnection using main thread inside NSOperation class.
NSURLConnection's delegate is set to NSOperation class object.
Call from NSURLConnection comes on main thread.
I need to process this data using the same operation thread. how do i achieve this ??
#implementation ModelCreationSearchOperation {
int try;
}
- (BOOL)isConcurrent
{
return YES;
}
- (void)start
{
[self willChangeValueForKey:#"isExecuting"];
_isExecuting = YES;
[self didChangeValueForKey:#"isExecuting"];
dispatch_async(dispatch_get_main_queue(), ^{
if (self.isCancelled) {
[self finish];
return;
}
});
[self fetchData];
}
-(void)fetchData {
dispatch_async(dispatch_get_main_queue(), ^{
self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
});
}
- (void)finish
{
[self willChangeValueForKey:#"isExecuting"];
[self willChangeValueForKey:#"isFinished"];
_isExecuting = NO;
_isFinished = YES;
[self didChangeValueForKey:#"isExecuting"];
[self didChangeValueForKey:#"isFinished"];
[self cancel];
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
//Main thread
//Want to perform parsing of response data on operation thread ....
}
You say that you "want to perform parsing of response data on operation thread." Do you really need to run it on the operation thread, or do you just need to get it off the main thread? The operation queue doesn't necessarily have a single, dedicated thread, so the question doesn't quite make sense. (It's one of the beauties of dispatch queues and operation queues, that it manages the threads for us and we generally don't have to get involved in those details.)
If you simply want the code in connectionDidFinishLoading to run on a background thread (if, for example, you're doing something exceptionally slow in this delegate method), just dispatch it to a background thread (you could use a global queue for that). If you want a serial queue for these connectionDidFinishLoading calls, create your own serial queue for that and dispatch this code to that queue. But if it's not too computationally intensive (e.g. parsing JSON or something like that), you can often just let it run on the main thread without incident.
As an aside, you can, if you really want, create a dedicated thread for your NSURLConnection delegate calls, and schedule the connection on that thread, but it's generally overkill. But see AFNetworking code for example of this implementation. This is illustrated in How do I start an Asychronous NSURLConnection inside an NSOperation?
I'm trying to figure out what is the difference between those 2.
Does it mean currentQueue cannot be mainQueue or it's a wrong assumption?
currentQueue return mainQueue if you call it in main-thread.
new is new queue with new threads
new is initializer method which NSOperationQueue inherits from NSObject
Documentation says:
This method is a combination of alloc and init. Like alloc, it initializes the isa instance variable of the new object so it points to the class data structure. It then invokes the init method to complete the initialization process.
This means calling +new creates new instance of NSOperationQueue
currentQueue returns you the queue on which the method was called.
NSOperationQueue docs of currentQueue says:
The operation queue that started the operation or nil if the queue could not be determined
I.e. if method calling +currentQueue is mainQueue, it can return mainQueue
prove of concept write by #Cy-4AH. Hop this can clarify a bit.
-(void) viewDidLoad {
NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^(void){
//this block will executed in a separate thread (not the main thread)
if ([NSOperationQueue currentQueue] == [NSOperationQueue mainQueue]) {
NSLog(#"= in block");
} else {
NSLog(#"not = in block"); //This will be log
}
}];
NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
[operationQueue addOperation:blockOperation];
//this block will executed in the main thread
if ([NSOperationQueue currentQueue] == [NSOperationQueue mainQueue]) {
NSLog(#"= outside of block"); //This will be log
} else {
NSLog(#"not = outside of block");
}
}
I am downloading four plist files asynchronously over the internet. I need to wait until all four files are downloaded, until I either on the first run, push a UIViewController, or on all subsequent runs, refresh the data, and reload all my UITableViews.
On the first run, everything works perfectly. When refreshing though, all four url requests are called, and started, but never call their completion or failure blocks, and the UI freezes. Which is odd since I preform all operations in a background thread. I have not been able to figure out why this is happening.
The first load and the refresh methods call the four "update" methods in the same way, and use NSCondition in the same way.
For the first run:
- (void)loadContentForProgram:(NSString *)programPath
{
NSLog(#"Start Load Program");
AppDelegate *myDelegate = (AppDelegate *)[UIApplication sharedApplication].delegate;
hud = [[MBProgressHUD alloc] initWithView:myDelegate.window];
[myDelegate.window addSubview:hud];
hud.labelText = #"Loading...";
hud.detailsLabelText = #"Loading Data";
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
//Do stuff here to load data from files
//Update From online files
hud.detailsLabelText = #"Updating Live Data";
resultLock = NO;
progressLock = NO;
recallLock = NO;
stageLock = NO;
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCurrentCompsText];
[self updateCompetitionResults];
[self updateCompetitionRecalls];
[self updateCompetitionProgress];
while (!resultLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(#"Unlock");
[condition unlock];
updateInProgress = NO;
//Reset Refresh controls and table views
self.refreshControlsArray = [[NSMutableArray alloc] init];
self.tableViewsArray = [[NSMutableArray alloc] init];
NSLog(#"Finished Loading Program");
[[NSNotificationCenter defaultCenter] postNotificationName:#"WMSOFinishedLoadingProgramData" object:nil]; //Pushes view controller
dispatch_async(dispatch_get_main_queue(), ^{
[MBProgressHUD hideHUDForView:myDelegate.window animated:YES];
});
});
}
When refreshing data:
- (void)updateProgramContent
{
if (!updateInProgress) {
updateInProgress = YES;
for (int i = 0; i < self.refreshControlsArray.count; i++) {
if (!((UIRefreshControl *)self.refreshControlsArray[i]).refreshing) {
[self.refreshControlsArray[i] beginRefreshing];
[self.tableViewsArray[i] setContentOffset:CGPointMake(0.0, 0.0) animated:YES];
}
}
resultLock = NO;
stageLock = NO;
recallLock = NO;
progressLock = NO;
dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
condition = [[NSCondition alloc] init];
[condition lock];
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
while (!resultLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!stageLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!recallLock) {
[condition wait];
}
NSLog(#"Unlock");
while (!progressLock) {
[condition wait];
}
NSLog(#"Unlock");
[condition unlock];
});
for (int i = 0; i < self.refreshControlsArray.count; i++) {
[self.refreshControlsArray[i] performSelector:#selector(endRefreshing) withObject:nil afterDelay:1.0];
[self.tableViewsArray[i] performSelector:#selector(reloadData) withObject:nil afterDelay:1.0];
}
updateInProgress = NO;
}
}
The block below that appears in each loading method above, corresponds to a method that will download and update a specific piece of data.
[self updateCompetitionProgress];
[self updateCompetitionRecalls];
[self updateCompetitionResults];
[self updateCurrentCompsText];
which runs:
- (void)updateCompetitionResults
{
__block NSDictionary *competitionResultsData = nil;
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:#"Some URL",[self.programName stringByReplacingOccurrencesOfString:#" " withString:#"%20"]]] cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:20.0];
AFPropertyListRequestOperation *operation = [AFPropertyListRequestOperation propertyListRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id propertyList) {
competitionResultsData = (NSDictionary *)propertyList;
[competitionResultsData writeToFile:[#"SOME LOCAL PATH"] atomically:NO];
[self updateCompetitionResultsWithDictionary:competitionResultsData];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id propertyList) {
competitionResultsData = [NSDictionary dictionaryWithContentsOfFile:[#"SOME LOCAL PATH"]];
NSLog(#"Failed to retreive competition results: %#", error);
[self updateCompetitionResultsWithDictionary:competitionResultsData];
}];
[operation start];
}
and the completion and failure blocks call the same method to update the data
- (void)updateCompetitionResultsWithDictionary:(NSDictionary *)competitionResultsData
{
//Do Stuff with the data here
resultLock = YES;
[condition signal];
}
So, Why does this work on the first run, but not any of the subsequent runs?
As I mentioned in my comments, above, the most obvious problem is that you're invoking methods that use condition before you initialize condition. Make sure initialize condition before you start calling updateCompetitionResults, etc.
In terms of a more radical change, I might suggest retiring NSCondition altogether, and use operation queues:
I might use NSOperationQueue (or you can use dispatch groups, too, if you want, but I like the operation queue's ability to configure how many concurrent operations you can operate ... also if you get to a point that you want to cancel operations, I think NSOperationQueue offers some nice features there, too). You can then define each download and processing as a separate NSOperation (each of the downloads should happen synchronously, because they're running in an operation queue, you get the benefits of asynchronous operations, but you can kick off the post-processing immediately after the download is done). You then just queue them up to run asynchronously, but define a final operation which is dependent upon the other four will kick off as soon as the four downloads are done. (By the way, I use NSBlockOperation which provides block-functionality for NSOperation objects, but you can do it any way you want.)
And whereas your updateProgramContent might download asynchronously, it processes the four downloaded files sequentially, one after another. Thus, if the first download takes a while to download, it will hold up the post-processing of the others. Instead, I like to encapsulate both the downloading and the post processing of each of the four plist files in a single NSOperation, each. Thus, we enjoy maximal concurrency of not only the downloading, but the post-processing, too.
Rather than using the AFNetworking (which I'm generally a big fan of) plist-related method, I might be inclined to use NSDictionary and NSArray features that allow you to download a plist from the web and load them into the appropriate structure. These dictionaryWithContentsOfURL and arrayWithContentsOfURL run synchronously, but because we're doing this in a background operation, everything runs asynchronously like you want. This also bypasses the saving them to files. If you wanted them saved to files in your Documents directory, you can do that easily, too. Clearly, if you're doing something sophisticated in your downloading of the plist files (e.g. your server is engaging in some challenge-response authentication), you can't use the convenient NSDictionary and NSArray methods. But if you don't need all of that, the simple NSDictionary and NSArray methods, ___WithContentsOfURL make life pretty simple.
Pulling this all together, it might look like:
#interface ViewController ()
#property (nonatomic, strong) NSArray *competitions;
#property (nonatomic, strong) NSDictionary *competitionResults;
#property (nonatomic, strong) NSDictionary *competitionRecalls;
#property (nonatomic, strong) NSDictionary *competitionProgress;
#end
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self transfer];
}
- (void)allTransfersComplete
{
BOOL success;
if (self.competitions == nil)
{
success = FALSE;
NSLog(#"Unable to download competitions");
}
if (self.competitionResults == nil)
{
success = FALSE;
NSLog(#"Unable to download results");
}
if (self.competitionRecalls == nil)
{
success = FALSE;
NSLog(#"Unable to download recalls");
}
if (self.competitionProgress == nil)
{
success = FALSE;
NSLog(#"Unable to download progress");
}
if (success)
{
NSLog(#"all done successfully");
}
else
{
NSLog(#"one or more failed");
}
}
- (void)transfer
{
NSURL *baseUrl = [NSURL URLWithString:#"http://insert.your.base.url.here/competitions"];
NSURL *competitionsUrl = [baseUrl URLByAppendingPathComponent:#"competitions.plist"];
NSURL *competitionResultsUrl = [baseUrl URLByAppendingPathComponent:#"competitionresults.plist"];
NSURL *competitionRecallsUrl = [baseUrl URLByAppendingPathComponent:#"competitionrecalls.plist"];
NSURL *competitionProgressUrl = [baseUrl URLByAppendingPathComponent:#"competitionprogress.plist"];
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
queue.maxConcurrentOperationCount = 4; // if your server doesn't like four concurrent requests, you can ratchet this back to whatever you want
// create operation that will be called when we're all done
NSBlockOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
// any stuff that can be done in background should be done here
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// any user interface stuff should be done here; I've just put this in a separate method so this method doesn't get too unwieldy
[self allTransfersComplete];
}];
}];
// a variable that we'll use as we create our four download/process operations
NSBlockOperation *operation;
// create competitions operation
operation = [NSBlockOperation blockOperationWithBlock:^{
// download the competitions and load it into the ivar
//
// note, if you *really* want to download this to a file, you can
// do that when the download is done
self.competitions = [NSArray arrayWithContentsOfURL:competitionsUrl];
// if you wanted to do any post-processing of the download
// you could do it here.
NSLog(#"competitions = %#", self.competitions);
}];
[completionOperation addDependency:operation];
// create results operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionResults = [NSDictionary dictionaryWithContentsOfURL:competitionResultsUrl];
NSLog(#"competitionResults = %#", self.competitionResults);
}];
[completionOperation addDependency:operation];
// create recalls operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionRecalls = [NSDictionary dictionaryWithContentsOfURL:competitionRecallsUrl];
NSLog(#"competitionRecalls = %#", self.competitionRecalls);
}];
[completionOperation addDependency:operation];
// create progress operation
operation = [NSBlockOperation blockOperationWithBlock:^{
self.competitionProgress = [NSDictionary dictionaryWithContentsOfURL:competitionProgressUrl];
NSLog(#"competitionProgress = %#", self.competitionProgress);
}];
[completionOperation addDependency:operation];
// queue the completion operation (which is dependent upon the other four)
[queue addOperation:completionOperation];
// now queue the four download and processing operations
[queue addOperations:completionOperation.dependencies waitUntilFinished:NO];
}
#end
Now, I don't know which of your plist's are arrays and which are dictionaries (in my example, I made competitions an array and the rest were dictionaries keyed by the competition id), but hopefully you get the idea of what I was shooting for. Maximize concurrency, eliminate NSCondition logic, really make the most of NSOperationQueue, etc.
This may be all to much to take in, but I only mention it as an alternative to NSCondition. If your current technique works, that's great. But the above outlines how I would tackle a challenge like this.