• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 /*
2  *
3  * Copyright 2015 gRPC authors.
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  *     http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  *
17  */
18 
19 #import <Foundation/Foundation.h>
20 
21 #import "GRXWriteable.h"
22 
23 /** States of a writer. */
24 typedef NS_ENUM(NSInteger, GRXWriterState) {
25 
26   /**
27    * The writer has not yet been given a writeable to which it can push its values. To have a writer
28    * transition to the Started state, send it a startWithWriteable: message.
29    *
30    * A writer's state cannot be manually set to this value.
31    */
32   GRXWriterStateNotStarted,
33 
34   /** The writer might push values to the writeable at any moment. */
35   GRXWriterStateStarted,
36 
37   /**
38    * The writer is temporarily paused, and won't send any more values to the writeable unless its
39    * state is set back to Started. The writer might still transition to the Finished state at any
40    * moment, and is allowed to send writesFinishedWithError: to its writeable.
41    */
42   GRXWriterStatePaused,
43 
44   /**
45    * The writer has released its writeable and won't interact with it anymore.
46    *
47    * One seldomly wants to set a writer's state to this value, as its writeable isn't notified with
48    * a writesFinishedWithError: message. Instead, sending finishWithError: to the writer will make
49    * it notify the writeable and then transition to this state.
50    */
51   GRXWriterStateFinished
52 };
53 
54 /**
55  * An GRXWriter object can produce, on demand, a sequence of values. The sequence may be produced
56  * asynchronously, and it may consist of any number of elements, including none or an infinite
57  * number.
58  *
59  * GRXWriter is the active dual of NSEnumerator. The difference between them is thus whether the
60  * object plays an active or passive role during usage: A user of NSEnumerator pulls values off it,
61  * and passes the values to a writeable. A user of GRXWriter, though, just gives it a writeable, and
62  * the GRXWriter instance pushes values to the writeable. This makes this protocol suitable to
63  * represent a sequence of future values, as well as collections with internal iteration.
64  *
65  * An instance of GRXWriter can start producing values after a writeable is passed to it. It can
66  * also be commanded to finish the sequence immediately (with an optional error). Finally, it can be
67  * asked to pause, and resumed later. All GRXWriter objects support pausing and early termination.
68  *
69  * Thread-safety:
70  *
71  * State transitions take immediate effect if the object is used from a single thread. Subclasses
72  * might offer stronger guarantees.
73  *
74  * Unless otherwise indicated by a conforming subclass, no messages should be sent concurrently to a
75  * GRXWriter. I.e., conforming classes aren't required to be thread-safe.
76  */
77 @interface GRXWriter : NSObject
78 
79 /**
80  * This property can be used to query the current state of the writer, which determines how it might
81  * currently use its writeable. Some state transitions can be triggered by setting this property to
82  * the corresponding value, and that's useful for advanced use cases like pausing an writer. For
83  * more details, see the documentation of the enum further down.
84  */
85 @property(nonatomic) GRXWriterState state;
86 
87 /**
88  * Transition to the Started state, and start sending messages to the writeable (a reference to it
89  * is retained). Messages to the writeable may be sent before the method returns, or they may be
90  * sent later in the future. See GRXWriteable.h for the different messages a writeable can receive.
91  *
92  * If this writer draws its values from an external source (e.g. from the filesystem or from a
93  * server), calling this method will commonly trigger side effects (like network connections).
94  *
95  * This method might only be called on writers in the NotStarted state.
96  */
97 - (void)startWithWriteable:(id<GRXWriteable>)writeable;
98 
99 /**
100  * Send writesFinishedWithError:errorOrNil to the writeable. Then release the reference to it and
101  * transition to the Finished state.
102  *
103  * This method might only be called on writers in the Started or Paused state.
104  */
105 - (void)finishWithError:(NSError *)errorOrNil;
106 @end
107