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/*
*
* Copyright 2015, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#import "GRXConcurrentWriteable.h"
#import <RxLibrary/GRXWriteable.h>
@interface GRXConcurrentWriteable ()
// This is atomic so that cancellation can nillify it from any thread.
@property(atomic, strong) id<GRXWriteable> writeable;
@end
@implementation GRXConcurrentWriteable {
dispatch_queue_t _writeableQueue;
// This ensures that writesFinishedWithError: is only sent once to the writeable.
dispatch_once_t _alreadyFinished;
}
- (instancetype)init {
return [self initWithWriteable:nil];
}
// Designated initializer
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable {
if (self = [super init]) {
_writeableQueue = dispatch_get_main_queue();
_writeable = writeable;
}
return self;
}
- (void)enqueueValue:(id)value completionHandler:(void (^)())handler {
dispatch_async(_writeableQueue, ^{
// We're racing a possible cancellation performed by another thread. To turn all already-
// enqueued messages into noops, cancellation nillifies the writeable property. If we get it
// before it's nil, we won the race.
id<GRXWriteable> writeable = self.writeable;
if (writeable) {
[writeable writeValue:value];
handler();
}
});
}
- (void)enqueueSuccessfulCompletion {
dispatch_async(_writeableQueue, ^{
dispatch_once(&_alreadyFinished, ^{
// Cancellation is now impossible. None of the other three blocks can run concurrently with
// this one.
[self.writeable writesFinishedWithError:nil];
// Skip any possible message to the wrapped writeable enqueued after this one.
self.writeable = nil;
});
});
}
- (void)cancelWithError:(NSError *)error {
NSAssert(error, @"For a successful completion, use enqueueSuccessfulCompletion.");
dispatch_once(&_alreadyFinished, ^{
// Skip any of the still-enqueued messages to the wrapped writeable. We use the atomic setter to
// nillify writeable because we might be running concurrently with the blocks in
// _writeableQueue, and assignment with ARC isn't atomic.
id<GRXWriteable> writeable = self.writeable;
self.writeable = nil;
dispatch_async(_writeableQueue, ^{
[writeable writesFinishedWithError:error];
});
});
}
- (void)cancelSilently {
dispatch_once(&_alreadyFinished, ^{
// Skip any of the still-enqueued messages to the wrapped writeable. We use the atomic setter to
// nillify writeable because we might be running concurrently with the blocks in
// _writeableQueue, and assignment with ARC isn't atomic.
self.writeable = nil;
});
}
@end
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