Initial checkin of gRPC to third_party/

third_party/grpc/src/objective-c/RxLibrary/GRXWriter.h

+/*
+ *
+ * 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 "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.
+ */
+@property(nonatomic) 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