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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 <Foundation/Foundation.h>
#import "GRXWriteable.h"
/** States of a writer. */
typedef NS_ENUM(NSInteger, GRXWriterState) {
/**
* The writer has not yet been given a writeable to which it can push its values. To have a writer
* transition to the Started state, send it a startWithWriteable: message.
*
* A writer's state cannot be manually set to this value.
*/
GRXWriterStateNotStarted,
/** The writer might push values to the writeable at any moment. */
GRXWriterStateStarted,
/**
* The writer is temporarily paused, and won't send any more values to the writeable unless its
* state is set back to Started. The writer might still transition to the Finished state at any
* moment, and is allowed to send writesFinishedWithError: to its writeable.
*/
GRXWriterStatePaused,
/**
* The writer has released its writeable and won't interact with it anymore.
*
* One seldomly wants to set a writer's state to this value, as its writeable isn't notified with
* a writesFinishedWithError: message. Instead, sending finishWithError: to the writer will make
* it notify the writeable and then transition to this state.
*/
GRXWriterStateFinished
};
/**
* An GRXWriter object can produce, on demand, a sequence of values. The sequence may be produced
* asynchronously, and it may consist of any number of elements, including none or an infinite
* number.
*
* GRXWriter is the active dual of NSEnumerator. The difference between them is thus whether the
* object plays an active or passive role during usage: A user of NSEnumerator pulls values off it,
* and passes the values to a writeable. A user of GRXWriter, though, just gives it a writeable, and
* the GRXWriter instance pushes values to the writeable. This makes this protocol suitable to
* represent a sequence of future values, as well as collections with internal iteration.
*
* An instance of GRXWriter can start producing values after a writeable is passed to it. It can
* also be commanded to finish the sequence immediately (with an optional error). Finally, it can be
* asked to pause, and resumed later. All GRXWriter objects support pausing and early termination.
*
* Thread-safety:
*
* State transitions take immediate effect if the object is used from a single thread. Subclasses
* might offer stronger guarantees.
*
* Unless otherwise indicated by a conforming subclass, no messages should be sent concurrently to a
* GRXWriter. I.e., conforming classes aren't required to be thread-safe.
*/
@interface GRXWriter : NSObject
/**
* This property can be used to query the current state of the writer, which determines how it might
* currently use its writeable. Some state transitions can be triggered by setting this property to
* the corresponding value, and that's useful for advanced use cases like pausing an writer. For
* more details, see the documentation of the enum further down. The property is thread safe.
*/
@property(atomic) GRXWriterState state;
/**
* Transition to the Started state, and start sending messages to the writeable (a reference to it
* is retained). Messages to the writeable may be sent before the method returns, or they may be
* sent later in the future. See GRXWriteable.h for the different messages a writeable can receive.
*
* If this writer draws its values from an external source (e.g. from the filesystem or from a
* server), calling this method will commonly trigger side effects (like network connections).
*
* This method might only be called on writers in the NotStarted state.
*/
- (void)startWithWriteable:(id<GRXWriteable>)writeable;
/**
* Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and
* transition to the Finished state.
*
* This method might only be called on writers in the Started or Paused state.
*/
- (void)finishWithError:(NSError *)errorOrNil;
@end
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