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/*
*
* Copyright 2015 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#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.
BOOL _alreadyFinished;
}
- (instancetype)init {
return [self initWithWriteable:nil];
}
// Designated initializer
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable
dispatchQueue:(dispatch_queue_t)queue {
if (self = [super init]) {
_writeableQueue = queue;
_writeable = writeable;
}
return self;
}
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable {
return [self initWithWriteable:writeable
dispatchQueue:dispatch_get_main_queue()];
}
- (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, ^{
BOOL finished = NO;
@synchronized (self) {
if (!_alreadyFinished) {
_alreadyFinished = YES;
} else {
finished = YES;
}
}
if (!finished) {
// 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.");
BOOL finished = NO;
@synchronized (self) {
if (!_alreadyFinished) {
_alreadyFinished = YES;
} else {
finished = YES;
}
}
if (!finished) {
// 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 {
BOOL finished = NO;
@synchronized (self) {
if (!_alreadyFinished) {
_alreadyFinished = YES;
} else {
finished = YES;
}
}
if (!finished) {
// 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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