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diff --git a/src/objective-c/RxLibrary/GRXConcurrentWriteable.h b/src/objective-c/RxLibrary/GRXConcurrentWriteable.h
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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 <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 NS_DESIGNATED_INITIALIZER;
+
+// 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