annotate Implab/Promise.cs @ 4:381095ad0a69

Implab.Fx: implemented animation object Implab.Fx: implemented transparency animation helper
author cin
date Tue, 17 Sep 2013 04:27:30 +0400
parents aa367305156b
children dfa21d507bc5
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1 using System;
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2 using System.Collections.Generic;
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3 using System.Linq;
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4 using System.Reflection;
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5 using System.Text;
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6 using System.Diagnostics;
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7 using System.Threading;
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8
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9 namespace Implab {
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10
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11 public delegate void ErrorHandler(Exception e);
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12
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13 public delegate void ResultHandler<T>(T result);
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14 public delegate TNew ResultMapper<TSrc,TNew>(TSrc result);
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15 public delegate Promise<TNew> ChainedOperation<TSrc,TNew>(TSrc result);
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16
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17 /// <summary>
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18 /// Класс для асинхронного получения результатов. Так называемое "обещание".
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19 /// </summary>
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20 /// <typeparam name="T">Тип получаемого результата</typeparam>
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21 /// <remarks>
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22 /// <para>Сервис при обращении к его методу дает обещаиние о выполнении операции,
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23 /// клиент получив такое обещание может установить ряд обратных вызово для получения
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24 /// событий выполнения обещания, тоесть завершения операции и предоставлении результатов.</para>
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25 /// <para>
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26 /// Обещение может быть как выполнено, так и выполнено с ошибкой. Для подписки на
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27 /// данные события клиент должен использовать методы <c>Then</c>.
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28 /// </para>
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29 /// <para>
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30 /// Сервис, в свою очередь, по окончанию выполнения операции (возможно с ошибкой),
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31 /// использует методы <c>Resolve</c> либо <c>Reject</c> для оповещения клиетна о
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32 /// выполнении обещания.
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33 /// </para>
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34 /// <para>
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35 /// Если сервер успел выполнить обещание еще до того, как клиент на него подписался,
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36 /// то в момент подписки клиента будут вызваны соответсвующие события в синхронном
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37 /// режиме и клиент будет оповещен в любом случае. Иначе, обработчики добавляются в
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38 /// список в порядке подписания и в этом же порядке они будут вызваны при выполнении
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39 /// обещания.
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40 /// </para>
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41 /// <para>
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42 /// Обрабатывая результаты обещания можно преобразовывать результаты либо инициировать
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43 /// связанные асинхронные операции, которые также возвращают обещания. Для этого следует
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44 /// использовать соответствующую форму методе <c>Then</c>.
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45 /// </para>
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46 /// <para>
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47 /// Также хорошим правилом является то, что <c>Resolve</c> и <c>Reject</c> должен вызывать
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48 /// только инициатор обещания иначе могут возникнуть противоречия.
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49 /// </para>
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50 /// </remarks>
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51 public class Promise<T> {
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52
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53 struct ResultHandlerInfo {
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54 public ResultHandler<T> resultHandler;
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55 public ErrorHandler errorHandler;
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56 }
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57
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58 enum State {
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59 Unresolved,
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60 Resolving,
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61 Resolved,
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62 Cancelled
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63 }
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64
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65 LinkedList<ResultHandlerInfo> m_handlersChain = new LinkedList<ResultHandlerInfo>();
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66 State m_state;
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67 bool m_cancellable;
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68 T m_result;
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69 Exception m_error;
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70
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71 public Promise() {
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72 m_cancellable = true;
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73 }
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74
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75 /// <summary>
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76 /// Событие, возникающее при отмене асинхронной операции.
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77 /// </summary>
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78 /// <description>
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79 /// Как правило используется для оповещения объекта, выполняющего асинхронную операцию, о том, что ее следует отменить.
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80 /// </description>
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81 public event EventHandler Cancelled;
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82
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83 /// <summary>
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84 /// Выполняет обещание, сообщая об успешном выполнении.
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85 /// </summary>
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86 /// <param name="result">Результат выполнения.</param>
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87 /// <exception cref="InvalidOperationException">Данное обещание уже выполнено</exception>
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88 public void Resolve(T result) {
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89 lock (this) {
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90 if (m_state == State.Cancelled)
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91 return;
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92 if (m_state != State.Unresolved)
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93 throw new InvalidOperationException("The promise is already resolved");
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94 m_result = result;
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95 m_state = State.Resolving;
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96 }
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97
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98 ResultHandlerInfo handler;
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99 while (FetchNextHandler(out handler))
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100 InvokeHandler(handler);
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101 }
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102
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103 /// <summary>
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104 /// Выполняет обещание, сообщая об ошибке
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105 /// </summary>
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106 /// <param name="error">Исключение возникшее при выполнении операции</param>
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107 /// <exception cref="InvalidOperationException">Данное обещание уже выполнено</exception>
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108 public void Reject(Exception error) {
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109 lock (this) {
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110 if (m_state == State.Cancelled)
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111 return;
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112 if (m_state != State.Unresolved)
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113 throw new InvalidOperationException("The promise is already resolved");
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114 m_error = error;
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115 m_state = State.Resolving;
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116 }
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117
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118 ResultHandlerInfo handler;
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119 while (FetchNextHandler(out handler))
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120 InvokeHandler(handler);
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121 }
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122
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123 /// <summary>
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124 /// Отменяет операцию, если это возможно.
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125 /// </summary>
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126 /// <returns><c>true</c> Операция была отменена, обработчики не будут вызваны.<c>false</c> отмена не возможна, поскольку обещание уже выполнено и обработчики отработали.</returns>
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127 public bool Cancel() {
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128 lock(this) {
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129 if (m_state == State.Unresolved && m_cancellable) {
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130 m_state = State.Cancelled;
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131 EventHandler temp = Cancelled;
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132
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133 if (temp != null)
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134 temp(this,new EventArgs());
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135
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136 return true;
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137 } else
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138 return false;
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139 }
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140 }
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141
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142 /// <summary>
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143 /// Добавляет обработчики событий выполнения обещания.
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144 /// </summary>
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145 /// <param name="success">Обработчик успешного выполнения обещания.
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146 /// Данному обработчику будет передан результат выполнения операции.</param>
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147 /// <param name="error">Обработчик ошибки. Данный обработчик получит
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148 /// исключение возникшее при выполнении операции.</param>
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149 /// <returns>Само обещание</returns>
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150 public Promise<T> Then(ResultHandler<T> success, ErrorHandler error) {
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151 if (success == null && error == null)
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152 return this;
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153
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154 AddHandler(new ResultHandlerInfo() {
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155 resultHandler = success,
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156 errorHandler = error
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157 });
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158
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159 return this;
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160 }
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161
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162 public Promise<T> Then(ResultHandler<T> success) {
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163 return Then (success, null);
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164 }
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165
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166 public Promise<T> Anyway(Action handler) {
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167 if (handler == null)
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168 return this;
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169 AddHandler(new ResultHandlerInfo {
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170 resultHandler = x => handler(),
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171 errorHandler = x => handler()
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172 });
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173
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174 return this;
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175 }
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176
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177 /// <summary>
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178 /// Позволяет преобразовать результат выполения операции к новому типу.
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179 /// </summary>
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180 /// <typeparam name="TNew">Новый тип результата.</typeparam>
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181 /// <param name="mapper">Преобразование результата к новому типу.</param>
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182 /// <param name="error">Обработчик ошибки. Данный обработчик получит
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183 /// исключение возникшее при выполнении операции.</param>
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184 /// <returns>Новое обещание, которое будет выполнено при выполнении исходного обещания.</returns>
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185 public Promise<TNew> Map<TNew>(ResultMapper<T, TNew> mapper, ErrorHandler error) {
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186 if (mapper == null)
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187 throw new ArgumentNullException("mapper");
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188
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189 // создаем прицепленное обещание
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190 Promise<TNew> chained = new Promise<TNew>();
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191
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192 AddHandler(new ResultHandlerInfo() {
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193 resultHandler = delegate(T result) {
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194 try {
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195 // если преобразование выдаст исключение, то сработает reject сцепленного deferred
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196 chained.Resolve(mapper(result));
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197 } catch (Exception e) {
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198 chained.Reject(e);
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199 }
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200 },
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201 errorHandler = delegate(Exception e) {
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202 if (error != null)
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203 error(e);
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204 // в случае ошибки нужно передать исключение дальше по цепочке
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205 chained.Reject(e);
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206 }
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207 });
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208
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209 return chained;
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210 }
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211
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212 public Promise<TNew> Map<TNew>(ResultMapper<T, TNew> mapper) {
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213 return Map (mapper, null);
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214 }
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215
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216 /// <summary>
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217 /// Сцепляет несколько аснхронных операций. Указанная асинхронная операция будет вызвана после
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218 /// выполнения текущей, а результат текущей операции может быть использован для инициализации
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219 /// новой операции.
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220 /// </summary>
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221 /// <typeparam name="TNew">Тип результата указанной асинхронной операции.</typeparam>
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222 /// <param name="chained">Асинхронная операция, которая должна будет начаться после выполнения текущей.</param>
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223 /// <param name="error">Обработчик ошибки. Данный обработчик получит
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224 /// исключение возникшее при выполнении текуещй операции.</param>
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225 /// <returns>Новое обещание, которое будет выполнено по окончанию указанной аснхронной операции.</returns>
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226 public Promise<TNew> Chain<TNew>(ChainedOperation<T, TNew> chained, ErrorHandler error) {
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227
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228 // проблема в том, что на момент связывания еще не начата асинхронная операция, поэтому нужно
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229 // создать посредника, к которому будут подвызяваться следующие обработчики.
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230 // когда будет выполнена реальная асинхронная операция, она обратиться к посреднику, чтобы
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231 // передать через него результаты работы.
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232 Promise<TNew> medium = new Promise<TNew>();
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233
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234 AddHandler(new ResultHandlerInfo() {
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235 resultHandler = delegate(T result) {
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236 try {
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237 chained(result).Then(
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238 x => medium.Resolve(x),
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239 e => medium.Reject(e)
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240 );
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241 } catch(Exception e) {
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242 // если сцепленное действие выдало исключение вместо обещания, то передаем ошибку по цепочке
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243 medium.Reject(e);
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244 }
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245 },
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246 errorHandler = delegate(Exception e) {
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247 if (error != null)
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248 error(e);
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249 // в случае ошибки нужно передать исключение дальше по цепочке
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250 medium.Reject(e);
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251 }
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252 });
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253
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254 return medium;
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255 }
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256
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257 public Promise<TNew> Chain<TNew>(ChainedOperation<T, TNew> chained) {
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258 return Chain (chained, null);
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259 }
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260
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261 /// <summary>
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262 /// Дожидается отложенного обещания и в случае успеха, возвращает
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263 /// его, результат, в противном случае бросает исключение.
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264 /// </summary>
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265 /// <remarks>
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266 /// <para>
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267 /// Если ожидание обещания было прервано по таймауту, это не значит,
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268 /// что обещание было отменено или что-то в этом роде, это только
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269 /// означает, что мы его не дождались, однако все зарегистрированные
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270 /// обработчики, как были так остались и они будут вызваны, когда
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271 /// обещание будет выполнено.
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272 /// </para>
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273 /// <para>
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274 /// Такое поведение вполне оправдано поскольку таймаут может истечь
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275 /// в тот момент, когда началась обработка цепочки обработчиков, и
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276 /// к тому же текущее обещание может стоять в цепочке обещаний и его
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277 /// отклонение может привести к непрогнозируемому результату.
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278 /// </para>
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279 /// </remarks>
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280 /// <param name="timeout">Время ожидания</param>
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281 /// <returns>Результат выполнения обещания</returns>
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282 public T Join(int timeout) {
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283 ManualResetEvent evt = new ManualResetEvent(false);
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284 Anyway(() => evt.Set());
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285
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286 if (!evt.WaitOne(timeout, true))
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287 throw new TimeoutException();
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288
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289 if (m_error != null)
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290 throw new TargetInvocationException( m_error );
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291 else
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292 return m_result;
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293 }
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294
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295 public T Join() {
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296 return Join(Timeout.Infinite);
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297 }
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298
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299 /// <summary>
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300 /// Данный метод последовательно извлекает обработчики обещания и когда
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301 /// их больше не осталось - ставит состояние "разрешено".
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302 /// </summary>
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303 /// <param name="handler">Информация об обработчике</param>
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304 /// <returns>Признак того, что еще остались обработчики в очереди</returns>
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305 bool FetchNextHandler(out ResultHandlerInfo handler) {
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306 handler = default(ResultHandlerInfo);
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307
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308 lock (this) {
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309 Debug.Assert(m_state == State.Resolving);
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310
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311 if (m_handlersChain.Count > 0) {
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312 handler = m_handlersChain.First.Value;
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313 m_handlersChain.RemoveFirst();
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314 return true;
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315 } else {
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316 m_state = State.Resolved;
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317 return false;
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318 }
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319 }
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320 }
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321
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322 void AddHandler(ResultHandlerInfo handler) {
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323 bool invokeRequired = false;
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324
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325 lock (this) {
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326 if (m_state != State.Resolved)
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327 m_handlersChain.AddLast(handler);
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328 else
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329 invokeRequired = true;
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330 }
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331
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332 // обработчики не должны блокировать сам объект
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333 if (invokeRequired)
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334 InvokeHandler(handler);
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335 }
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336
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337 void InvokeHandler(ResultHandlerInfo handler) {
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338 if (m_error == null) {
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339 try {
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340 if (handler.resultHandler != null)
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341 handler.resultHandler(m_result);
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342 } catch { }
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343 }
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344
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345 if (m_error != null) {
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346 try {
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347 if (handler.errorHandler !=null)
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348 handler.errorHandler(m_error);
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349 } catch { }
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350 }
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351 }
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352
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353
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354 }
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355 }