| /* |
| * |
| * 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 |