Bolts/Common/BFTask.m

/*
 *  Copyright (c) 2014, Facebook, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

#import "BFTask.h"

#import <libkern/OSAtomic.h>

#import "Bolts.h"

NS_ASSUME_NONNULL_BEGIN

__attribute__ ((noinline)) void warnBlockingOperationOnMainThread() {
    NSLog(@"Warning: A long-running operation is being executed on the main thread. \n"
          " Break on warnBlockingOperationOnMainThread() to debug.");
}

NSString *const BFTaskErrorDomain = @"bolts";
NSInteger const kBFMultipleErrorsError = 80175001;

NSString *const BFTaskMultipleErrorsUserInfoKey = @"errors";

@interface BFTask () {
    id _result;
    NSError *_error;
}

@property (nonatomic, assign, readwrite, getter=isCancelled) BOOL cancelled;
@property (nonatomic, assign, readwrite, getter=isFaulted) BOOL faulted;
@property (nonatomic, assign, readwrite, getter=isCompleted) BOOL completed;

@property (nonatomic, strong) NSObject *lock;
@property (nonatomic, strong) NSCondition *condition;
@property (nonatomic, strong) NSMutableArray *callbacks;

@end

@implementation BFTask

#pragma mark - Initializer

- (instancetype)init {
    self = [super init];
    if (!self) return self;

    _lock = [[NSObject alloc] init];
    _condition = [[NSCondition alloc] init];
    _callbacks = [NSMutableArray array];

    return self;
}

- (instancetype)initWithResult:(nullable id)result {
    self = [super init];
    if (!self) return self;

    [self trySetResult:result];

    return self;
}

- (instancetype)initWithError:(NSError *)error {
    self = [super init];
    if (!self) return self;

    [self trySetError:error];

    return self;
}

- (instancetype)initCancelled {
    self = [super init];
    if (!self) return self;

    [self trySetCancelled];

    return self;
}

#pragma mark - Task Class methods

+ (instancetype)taskWithResult:(nullable id)result {
    return [[self alloc] initWithResult:result];
}

+ (instancetype)taskWithError:(NSError *)error {
    return [[self alloc] initWithError:error];
}

+ (instancetype)cancelledTask {
    return [[self alloc] initCancelled];
}

+ (instancetype)taskForCompletionOfAllTasks:(nullable NSArray<BFTask *> *)tasks {
    __block int32_t total = (int32_t)tasks.count;
    if (total == 0) {
        return [self taskWithResult:nil];
    }

    __block int32_t cancelled = 0;
    NSObject *lock = [[NSObject alloc] init];
    NSMutableArray *errors = [NSMutableArray array];

    BFTaskCompletionSource *tcs = [BFTaskCompletionSource taskCompletionSource];
    for (BFTask *task in tasks) {
        [task continueWithBlock:^id(BFTask *t) {
            if (t.error) {
                @synchronized (lock) {
                    [errors addObject:t.error];
                }
            } else if (t.cancelled) {
                OSAtomicIncrement32Barrier(&cancelled);
            }

            if (OSAtomicDecrement32Barrier(&total) == 0) {
                if (errors.count > 0) {
                    if (errors.count == 1) {
                        tcs.error = [errors firstObject];
                    } else {
                        NSError *error = [NSError errorWithDomain:BFTaskErrorDomain
                                                             code:kBFMultipleErrorsError
                                                         userInfo:@{ BFTaskMultipleErrorsUserInfoKey: errors }];
                        tcs.error = error;
                    }
                } else if (cancelled > 0) {
                    [tcs cancel];
                } else {
                    tcs.result = nil;
                }
            }
            return nil;
        }];
    }
    return tcs.task;
}

+ (instancetype)taskForCompletionOfAllTasksWithResults:(nullable NSArray<BFTask *> *)tasks {
    return [[self taskForCompletionOfAllTasks:tasks] continueWithSuccessBlock:^id(BFTask * __unused task) {
        return [tasks valueForKey:@"result"];
    }];
}

+ (instancetype)taskForCompletionOfAnyTask:(nullable NSArray<BFTask *> *)tasks
{
    __block int32_t total = (int32_t)tasks.count;
    if (total == 0) {
        return [self taskWithResult:nil];
    }
    
    __block int completed = 0;
    __block int32_t cancelled = 0;
    
    NSObject *lock = [NSObject new];
    NSMutableArray<NSError *> *errors = [NSMutableArray new];
    
    BFTaskCompletionSource *source = [BFTaskCompletionSource taskCompletionSource];
    for (BFTask *task in tasks) {
        [task continueWithBlock:^id(BFTask *t) {
            if (t.error != nil) {
                @synchronized(lock) {
                    [errors addObject:t.error];
                }
            } else if (t.cancelled) {
                OSAtomicIncrement32Barrier(&cancelled);
            } else {
                if(OSAtomicCompareAndSwap32Barrier(0, 1, &completed)) {
                    [source setResult:t.result];
                }
            }
            
            if (OSAtomicDecrement32Barrier(&total) == 0 &&
                OSAtomicCompareAndSwap32Barrier(0, 1, &completed)) {
                if (cancelled > 0) {
                    [source cancel];
                } else if (errors.count > 0) {
                    if (errors.count == 1) {
                        source.error = errors.firstObject;
                    } else {
                        NSError *error = [NSError errorWithDomain:BFTaskErrorDomain
                                                             code:kBFMultipleErrorsError
                                                         userInfo:@{ @"errors": errors }];
                        source.error = error;
                    }
                }
            }
            // Abort execution of per tasks continuations
            return nil;
        }];
    }
    return source.task;
}


+ (BFTask<BFVoid> *)taskWithDelay:(int)millis {
    BFTaskCompletionSource *tcs = [BFTaskCompletionSource taskCompletionSource];
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, millis * NSEC_PER_MSEC);
    dispatch_after(popTime, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
        tcs.result = nil;
    });
    return tcs.task;
}

+ (BFTask<BFVoid> *)taskWithDelay:(int)millis cancellationToken:(nullable BFCancellationToken *)token {
    if (token.cancellationRequested) {
        return [BFTask cancelledTask];
    }

    BFTaskCompletionSource *tcs = [BFTaskCompletionSource taskCompletionSource];
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, millis * NSEC_PER_MSEC);
    dispatch_after(popTime, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
        if (token.cancellationRequested) {
            [tcs cancel];
            return;
        }
        tcs.result = nil;
    });
    return tcs.task;
}

+ (instancetype)taskFromExecutor:(BFExecutor *)executor withBlock:(nullable id (^)(void))block {
    return [[self taskWithResult:nil] continueWithExecutor:executor withBlock:^id(BFTask *task) {
        return block();
    }];
}

#pragma mark - Custom Setters/Getters

- (nullable id)result {
    @synchronized(self.lock) {
        return _result;
    }
}

- (BOOL)trySetResult:(nullable id)result {
    @synchronized(self.lock) {
        if (self.completed) {
            return NO;
        }
        self.completed = YES;
        _result = result;
        [self runContinuations];
        return YES;
    }
}

- (nullable NSError *)error {
    @synchronized(self.lock) {
        return _error;
    }
}

- (BOOL)trySetError:(NSError *)error {
    @synchronized(self.lock) {
        if (self.completed) {
            return NO;
        }
        self.completed = YES;
        self.faulted = YES;
        _error = error;
        [self runContinuations];
        return YES;
    }
}

- (BOOL)isCancelled {
    @synchronized(self.lock) {
        return _cancelled;
    }
}

- (BOOL)isFaulted {
    @synchronized(self.lock) {
        return _faulted;
    }
}

- (BOOL)trySetCancelled {
    @synchronized(self.lock) {
        if (self.completed) {
            return NO;
        }
        self.completed = YES;
        self.cancelled = YES;
        [self runContinuations];
        return YES;
    }
}

- (BOOL)isCompleted {
    @synchronized(self.lock) {
        return _completed;
    }
}

- (void)runContinuations {
    @synchronized(self.lock) {
        [self.condition lock];
        [self.condition broadcast];
        [self.condition unlock];
        for (void (^callback)(void) in self.callbacks) {
            callback();
        }
        [self.callbacks removeAllObjects];
    }
}

#pragma mark - Chaining methods

- (BFTask *)continueWithExecutor:(BFExecutor *)executor withBlock:(BFContinuationBlock)block {
    return [self continueWithExecutor:executor block:block cancellationToken:nil];
}

- (BFTask *)continueWithExecutor:(BFExecutor *)executor
                           block:(BFContinuationBlock)block
               cancellationToken:(nullable BFCancellationToken *)cancellationToken {
    BFTaskCompletionSource *tcs = [BFTaskCompletionSource taskCompletionSource];

    // Capture all of the state that needs to used when the continuation is complete.
    dispatch_block_t executionBlock = ^{
        if (cancellationToken.cancellationRequested) {
            [tcs cancel];
            return;
        }

        id result = block(self);
        if ([result isKindOfClass:[BFTask class]]) {

            id (^setupWithTask) (BFTask *) = ^id(BFTask *task) {
                if (cancellationToken.cancellationRequested || task.cancelled) {
                    [tcs cancel];
                } else if (task.error) {
                    tcs.error = task.error;
                } else {
                    tcs.result = task.result;
                }
                return nil;
            };

            BFTask *resultTask = (BFTask *)result;

            if (resultTask.completed) {
                setupWithTask(resultTask);
            } else {
                [resultTask continueWithBlock:setupWithTask];
            }

        } else {
            tcs.result = result;
        }
    };

    BOOL completed;
    @synchronized(self.lock) {
        completed = self.completed;
        if (!completed) {
            [self.callbacks addObject:[^{
                [executor execute:executionBlock];
            } copy]];
        }
    }
    if (completed) {
        [executor execute:executionBlock];
    }

    return tcs.task;
}

- (BFTask *)continueWithBlock:(BFContinuationBlock)block {
    return [self continueWithExecutor:[BFExecutor defaultExecutor] block:block cancellationToken:nil];
}

- (BFTask *)continueWithBlock:(BFContinuationBlock)block cancellationToken:(nullable BFCancellationToken *)cancellationToken {
    return [self continueWithExecutor:[BFExecutor defaultExecutor] block:block cancellationToken:cancellationToken];
}

- (BFTask *)continueWithExecutor:(BFExecutor *)executor
                withSuccessBlock:(BFContinuationBlock)block {
    return [self continueWithExecutor:executor successBlock:block cancellationToken:nil];
}

- (BFTask *)continueWithExecutor:(BFExecutor *)executor
                    successBlock:(BFContinuationBlock)block
               cancellationToken:(nullable BFCancellationToken *)cancellationToken {
    if (cancellationToken.cancellationRequested) {
        return [BFTask cancelledTask];
    }

    return [self continueWithExecutor:executor block:^id(BFTask *task) {
        if (task.faulted || task.cancelled) {
            return task;
        } else {
            return block(task);
        }
    } cancellationToken:cancellationToken];
}

- (BFTask *)continueWithSuccessBlock:(BFContinuationBlock)block {
    return [self continueWithExecutor:[BFExecutor defaultExecutor] successBlock:block cancellationToken:nil];
}

- (BFTask *)continueWithSuccessBlock:(BFContinuationBlock)block cancellationToken:(nullable BFCancellationToken *)cancellationToken {
    return [self continueWithExecutor:[BFExecutor defaultExecutor] successBlock:block cancellationToken:cancellationToken];
}

#pragma mark - Syncing Task (Avoid it)

- (void)warnOperationOnMainThread {
    warnBlockingOperationOnMainThread();
}

- (void)waitUntilFinished {
    if ([NSThread isMainThread]) {
        [self warnOperationOnMainThread];
    }

    @synchronized(self.lock) {
        if (self.completed) {
            return;
        }
        [self.condition lock];
    }
    // TODO: (nlutsenko) Restructure this to use Bolts-Swift thread access synchronization architecture
    // In the meantime, it's absolutely safe to get `_completed` aka an ivar, as long as it's a `BOOL` aka less than word size.
    while (!_completed) {
        [self.condition wait];
    }
    [self.condition unlock];
}

#pragma mark - NSObject

- (NSString *)description {
    // Acquire the data from the locked properties
    BOOL completed;
    BOOL cancelled;
    BOOL faulted;
    NSString *resultDescription = nil;

    @synchronized(self.lock) {
        completed = self.completed;
        cancelled = self.cancelled;
        faulted = self.faulted;
        resultDescription = completed ? [NSString stringWithFormat:@" result = %@", self.result] : @"";
    }

    // Description string includes status information and, if available, the
    // result since in some ways this is what a promise actually "is".
    return [NSString stringWithFormat:@"<%@: %p; completed = %@; cancelled = %@; faulted = %@;%@>",
            NSStringFromClass([self class]),
            self,
            completed ? @"YES" : @"NO",
            cancelled ? @"YES" : @"NO",
            faulted ? @"YES" : @"NO",
            resultDescription];
}

@end

NS_ASSUME_NONNULL_END