src/objective-c/RxLibrary/GRXConcurrentWriteable.h

/*
 *
 * Copyright 2015, Google Inc.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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#import <Foundation/Foundation.h>

#import "GRXWriter.h"
#import "GRXWriteable.h"

/**
 * This is a thread-safe wrapper over a GRXWriteable instance. It lets one enqueue calls to a
 * GRXWriteable instance for the main thread, guaranteeing that writesFinishedWithError: is the last
 * message sent to it (no matter what messages are sent to the wrapper, in what order, nor from
 * which thread). It also guarantees that, if cancelWithError: is called from the main thread (e.g.
 * by the app cancelling the writes), no further messages are sent to the writeable except
 * writesFinishedWithError:.
 *
 * TODO(jcanizales): Let the user specify another queue for the writeable callbacks.
 */
@interface GRXConcurrentWriteable : NSObject

/**
 * The GRXWriteable passed is the wrapped writeable.
 * The GRXWriteable instance is retained until writesFinishedWithError: is sent to it, and released
 * after that.
 */
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable
                    dispatchQueue:(dispatch_queue_t)queue NS_DESIGNATED_INITIALIZER;
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable;

/**
 * Enqueues writeValue: to be sent to the writeable in the main thread.
 * The passed handler is invoked from the main thread after writeValue: returns.
 */
- (void)enqueueValue:(id)value completionHandler:(void (^)())handler;

/**
 * Enqueues writesFinishedWithError:nil to be sent to the writeable in the main thread. After that
 * message is sent to the writeable, all other methods of this object are effectively noops.
 */
- (void)enqueueSuccessfulCompletion;

/**
 * If the writeable has not yet received a writesFinishedWithError: message, this will enqueue one
 * to be sent to it in the main thread, and cancel all other pending messages to the writeable
 * enqueued by this object (both past and future).
 * The error argument cannot be nil.
 */
- (void)cancelWithError:(NSError *)error;

/**
 * Cancels all pending messages to the writeable enqueued by this object (both past and future).
 * Because the writeable won't receive writesFinishedWithError:, this also releases the writeable.
 */
- (void)cancelSilently;
@end