Таинственная проблема «постепенного замедления» в run loop / drawRect

Вот настоящая загадка.

Представьте, что вы выполняете обычный процесс рисования сложного изображения за пределами экрана (CGLayer) и периодически обновляете изображение на экране по мере рисования.

Как вы знаете, способ сделать это: запустить большой процесс рисования в фоновом режиме и вызов на передний план для setNeedsDisplays по желанию, вызывая обновление изображения. Это тривиально и достигается с помощью двух строк кода.

Однако, когда вы это делаете, возникает загадочная проблема: время, затрачиваемое на каждый цикл рисования, увеличивается каждый раз, становясь непригодным для использования . Кроме того, время может меняться беспорядочно.

Это известная ошибка iOS или? Кто-нибудь видел это раньше?

Вот чрезвычайно тривиальное и чрезвычайно простое для понимания приложение, демонстрирующее проблему:

http://www.fileswap.com/dl/p8lU3gAi/stepwiseDrawingV2.zip. html

Пример вывода ниже.

Кто-нибудь знает, почему это происходит? Это очень странное поведение ОС.

Позже ... FELZ придумал поразительный обходной путь. Фельц копирует CGLayer один раз за раунд. Это полностью останавливает странное поведение.

Однако до сих пор нет четкого понимания того, что, черт возьми, именно происходит: следовательно, буквально, где используется время, когда проявляется странная проблема?

А вот длинный пример того, как результат ...

Обратите внимание, что вы иногда получаете "вдвойне странный" результат, например следующий: он демонстрирует "нормальное" странное поведение: время увеличивается с каждым циклом. Тем не менее, иногда время падает до «невероятно быстрого» на пару раундов, а затем возвращается. Странно, да? В дальнейшем, если вы работаете на своем симуляторе, быстро переходите назад и вперед к несвязанным приложениям на вашем Mac для получения «еще более странных» результатов.

Хотя Фельц дал идеальный рабочий ответ, реальный механизм все еще остается загадкой.

:26:56.697 stepwiseDrawing[5334:1a03] time difference was     0
:26:56.707 stepwiseDrawing[5334:1a03] time difference was    10
:26:56.717 stepwiseDrawing[5334:1a03] time difference was    10
:26:56.744 stepwiseDrawing[5334:1a03] time difference was    27
:26:56.771 stepwiseDrawing[5334:1a03] time difference was    27
:26:56.807 stepwiseDrawing[5334:1a03] time difference was    37
:26:56.829 stepwiseDrawing[5334:1a03] time difference was    22
:26:56.864 stepwiseDrawing[5334:1a03] time difference was    35
:26:56.891 stepwiseDrawing[5334:1a03] time difference was    28
:26:56.936 stepwiseDrawing[5334:1a03] time difference was    45
:26:56.949 stepwiseDrawing[5334:1a03] time difference was    12
:26:56.981 stepwiseDrawing[5334:1a03] time difference was    32
:26:57.008 stepwiseDrawing[5334:1a03] time difference was    27
:26:57.041 stepwiseDrawing[5334:1a03] time difference was    33
:26:57.074 stepwiseDrawing[5334:1a03] time difference was    34
:26:57.109 stepwiseDrawing[5334:1a03] time difference was    34
:26:57.143 stepwiseDrawing[5334:1a03] time difference was    35
:26:57.179 stepwiseDrawing[5334:1a03] time difference was    36
:26:57.220 stepwiseDrawing[5334:1a03] time difference was    42
:26:57.271 stepwiseDrawing[5334:1a03] time difference was    51
:26:57.312 stepwiseDrawing[5334:1a03] time difference was    40
:26:57.356 stepwiseDrawing[5334:1a03] time difference was    45
:26:57.400 stepwiseDrawing[5334:1a03] time difference was    44
:26:57.447 stepwiseDrawing[5334:1a03] time difference was    46
:26:57.493 stepwiseDrawing[5334:1a03] time difference was    46
:26:57.542 stepwiseDrawing[5334:1a03] time difference was    49
:26:57.593 stepwiseDrawing[5334:1a03] time difference was    50
:26:57.707 stepwiseDrawing[5334:1a03] time difference was   114
:26:57.766 stepwiseDrawing[5334:1a03] time difference was    58
:26:57.801 stepwiseDrawing[5334:1a03] time difference was    36
:26:57.856 stepwiseDrawing[5334:1a03] time difference was    55
:26:57.918 stepwiseDrawing[5334:1a03] time difference was    62
:26:57.976 stepwiseDrawing[5334:1a03] time difference was    58
:26:58.039 stepwiseDrawing[5334:1a03] time difference was    62
:26:58.101 stepwiseDrawing[5334:1a03] time difference was    63
:26:58.165 stepwiseDrawing[5334:1a03] time difference was    63
:26:58.229 stepwiseDrawing[5334:1a03] time difference was    64
:26:58.294 stepwiseDrawing[5334:1a03] time difference was    66
:26:58.365 stepwiseDrawing[5334:1a03] time difference was    70
:26:58.436 stepwiseDrawing[5334:1a03] time difference was    72
:26:58.507 stepwiseDrawing[5334:1a03] time difference was    70
:26:58.572 stepwiseDrawing[5334:1a03] time difference was    65
:26:58.652 stepwiseDrawing[5334:1a03] time difference was    81
:26:58.726 stepwiseDrawing[5334:1a03] time difference was    74
:26:58.809 stepwiseDrawing[5334:1a03] time difference was    82
:26:58.879 stepwiseDrawing[5334:1a03] time difference was    70
:26:58.965 stepwiseDrawing[5334:1a03] time difference was    87
:26:59.043 stepwiseDrawing[5334:1a03] time difference was    77
:26:59.126 stepwiseDrawing[5334:1a03] time difference was    83
:26:59.210 stepwiseDrawing[5334:1a03] time difference was    84
:26:59.215 stepwiseDrawing[5334:1a03] time difference was     6
:26:59.310 stepwiseDrawing[5334:1a03] time difference was    95
:26:59.397 stepwiseDrawing[5334:1a03] time difference was    87
:26:59.486 stepwiseDrawing[5334:1a03] time difference was    89
:26:59.577 stepwiseDrawing[5334:1a03] time difference was    91
:26:59.668 stepwiseDrawing[5334:1a03] time difference was    91
:26:59.768 stepwiseDrawing[5334:1a03] time difference was   100
:26:59.856 stepwiseDrawing[5334:1a03] time difference was    88
:26:59.857 stepwiseDrawing[5334:1a03] time difference was     1
:26:59.965 stepwiseDrawing[5334:1a03] time difference was   108
:27:00.064 stepwiseDrawing[5334:1a03] time difference was   100
:27:00.165 stepwiseDrawing[5334:1a03] time difference was   101
:27:00.268 stepwiseDrawing[5334:1a03] time difference was   103
:27:00.371 stepwiseDrawing[5334:1a03] time difference was   103
:27:00.377 stepwiseDrawing[5334:1a03] time difference was     7
:27:00.493 stepwiseDrawing[5334:1a03] time difference was   115
:27:00.601 stepwiseDrawing[5334:1a03] time difference was   108
:27:00.710 stepwiseDrawing[5334:1a03] time difference was   109
:27:00.820 stepwiseDrawing[5334:1a03] time difference was   111
:27:00.939 stepwiseDrawing[5334:1a03] time difference was   119
:27:01.053 stepwiseDrawing[5334:1a03] time difference was   114
:27:01.162 stepwiseDrawing[5334:1a03] time difference was   108
:27:01.278 stepwiseDrawing[5334:1a03] time difference was   116
:27:01.396 stepwiseDrawing[5334:1a03] time difference was   118
:27:01.515 stepwiseDrawing[5334:1a03] time difference was   119
:27:01.637 stepwiseDrawing[5334:1a03] time difference was   122
:27:01.648 stepwiseDrawing[5334:1a03] time difference was    11
:27:01.769 stepwiseDrawing[5334:1a03] time difference was   121
:27:01.775 stepwiseDrawing[5334:1a03] time difference was     6
:27:01.910 stepwiseDrawing[5334:1a03] time difference was   135
:27:01.911 stepwiseDrawing[5334:1a03] time difference was     1
:27:02.045 stepwiseDrawing[5334:1a03] time difference was   134
:27:02.175 stepwiseDrawing[5334:1a03] time difference was   131
:27:02.314 stepwiseDrawing[5334:1a03] time difference was   139
:27:02.441 stepwiseDrawing[5334:1a03] time difference was   127
:27:02.586 stepwiseDrawing[5334:1a03] time difference was   145
:27:02.715 stepwiseDrawing[5334:1a03] time difference was   129
:27:02.853 stepwiseDrawing[5334:1a03] time difference was   138
:27:03.000 stepwiseDrawing[5334:1a03] time difference was   146
:27:03.133 stepwiseDrawing[5334:1a03] time difference was   134
:27:03.276 stepwiseDrawing[5334:1a03] time difference was   142
:27:03.419 stepwiseDrawing[5334:1a03] time difference was   143
:27:03.564 stepwiseDrawing[5334:1a03] time difference was   145
:27:03.717 stepwiseDrawing[5334:1a03] time difference was   153
:27:03.858 stepwiseDrawing[5334:1a03] time difference was   141
:27:04.008 stepwiseDrawing[5334:1a03] time difference was   149
:27:04.159 stepwiseDrawing[5334:1a03] time difference was   151
:27:04.318 stepwiseDrawing[5334:1a03] time difference was   159
:27:04.471 stepwiseDrawing[5334:1a03] time difference was   153
:27:04.620 stepwiseDrawing[5334:1a03] time difference was   149
:27:04.778 stepwiseDrawing[5334:1a03] time difference was   158
:27:04.939 stepwiseDrawing[5334:1a03] time difference was   161
:27:05.098 stepwiseDrawing[5334:1a03] time difference was   160
:27:05.269 stepwiseDrawing[5334:1a03] time difference was   171
:27:05.433 stepwiseDrawing[5334:1a03] time difference was   164
:27:05.600 stepwiseDrawing[5334:1a03] time difference was   166
:27:05.765 stepwiseDrawing[5334:1a03] time difference was   165
:27:05.932 stepwiseDrawing[5334:1a03] time difference was   167
:27:06.107 stepwiseDrawing[5334:1a03] time difference was   175
:27:06.269 stepwiseDrawing[5334:1a03] time difference was   163
:27:06.441 stepwiseDrawing[5334:1a03] time difference was   171
:27:06.617 stepwiseDrawing[5334:1a03] time difference was   176
:27:06.798 stepwiseDrawing[5334:1a03] time difference was   181
:27:06.971 stepwiseDrawing[5334:1a03] time difference was   173
:27:07.154 stepwiseDrawing[5334:1a03] time difference was   183
:27:07.326 stepwiseDrawing[5334:1a03] time difference was   172
:27:07.513 stepwiseDrawing[5334:1a03] time difference was   187
:27:07.689 stepwiseDrawing[5334:1a03] time difference was   176
:27:07.875 stepwiseDrawing[5334:1a03] time difference was   185
:27:08.059 stepwiseDrawing[5334:1a03] time difference was   184
:27:08.251 stepwiseDrawing[5334:1a03] time difference was   192
:27:08.432 stepwiseDrawing[5334:1a03] time difference was   181
:27:08.620 stepwiseDrawing[5334:1a03] time difference was   188
:27:08.811 stepwiseDrawing[5334:1a03] time difference was   190
:27:09.004 stepwiseDrawing[5334:1a03] time difference was   193
:27:09.195 stepwiseDrawing[5334:1a03] time difference was   191
:27:09.393 stepwiseDrawing[5334:1a03] time difference was   198
:27:09.590 stepwiseDrawing[5334:1a03] time difference was   197
:27:09.795 stepwiseDrawing[5334:1a03] time difference was   205
:27:09.989 stepwiseDrawing[5334:1a03] time difference was   193
:27:10.189 stepwiseDrawing[5334:1a03] time difference was   200
:27:10.392 stepwiseDrawing[5334:1a03] time difference was   203
:27:10.600 stepwiseDrawing[5334:1a03] time difference was   208
:27:10.801 stepwiseDrawing[5334:1a03] time difference was   202
:27:11.006 stepwiseDrawing[5334:1a03] time difference was   205
:27:11.220 stepwiseDrawing[5334:1a03] time difference was   213
:27:11.430 stepwiseDrawing[5334:1a03] time difference was   210
:27:11.633 stepwiseDrawing[5334:1a03] time difference was   203
:27:11.843 stepwiseDrawing[5334:1a03] time difference was   210
:27:12.055 stepwiseDrawing[5334:1a03] time difference was   213
:27:12.276 stepwiseDrawing[5334:1a03] time difference was   220
:27:12.484 stepwiseDrawing[5334:1a03] time difference was   208
:27:12.700 stepwiseDrawing[5334:1a03] time difference was   216
:27:12.919 stepwiseDrawing[5334:1a03] time difference was   219
:27:13.145 stepwiseDrawing[5334:1a03] time difference was   226
:27:13.360 stepwiseDrawing[5334:1a03] time difference was   215
:27:13.584 stepwiseDrawing[5334:1a03] time difference was   224
:27:13.813 stepwiseDrawing[5334:1a03] time difference was   229
:27:14.049 stepwiseDrawing[5334:1a03] time difference was   236
:27:14.269 stepwiseDrawing[5334:1a03] time difference was   220
:27:14.496 stepwiseDrawing[5334:1a03] time difference was   228
:27:14.725 stepwiseDrawing[5334:1a03] time difference was   229
:27:14.963 stepwiseDrawing[5334:1a03] time difference was   238
:27:15.196 stepwiseDrawing[5334:1a03] time difference was   232
:27:15.423 stepwiseDrawing[5334:1a03] time difference was   227
:27:15.657 stepwiseDrawing[5334:1a03] time difference was   235
:27:15.901 stepwiseDrawing[5334:1a03] time difference was   243
:27:16.133 stepwiseDrawing[5334:1a03] time difference was   232
:27:16.372 stepwiseDrawing[5334:1a03] time difference was   240
:27:16.613 stepwiseDrawing[5334:1a03] time difference was   241
:27:16.863 stepwiseDrawing[5334:1a03] time difference was   250
:27:17.101 stepwiseDrawing[5334:1a03] time difference was   238
:27:17.346 stepwiseDrawing[5334:1a03] time difference was   245
:27:17.593 stepwiseDrawing[5334:1a03] time difference was   247
:27:17.849 stepwiseDrawing[5334:1a03] time difference was   256
:27:18.093 stepwiseDrawing[5334:1a03] time difference was   244
:27:18.344 stepwiseDrawing[5334:1a03] time difference was   251
:27:18.603 stepwiseDrawing[5334:1a03] time difference was   260
:27:18.854 stepwiseDrawing[5334:1a03] time difference was   251
:27:19.114 stepwiseDrawing[5334:1a03] time difference was   259
:27:19.376 stepwiseDrawing[5334:1a03] time difference was   263
:27:19.646 stepwiseDrawing[5334:1a03] time difference was   270
:27:19.927 stepwiseDrawing[5334:1a03] time difference was   281
:27:20.202 stepwiseDrawing[5334:1a03] time difference was   274
:27:20.460 stepwiseDrawing[5334:1a03] time difference was   259
:27:20.743 stepwiseDrawing[5334:1a03] time difference was   283
:27:21.011 stepwiseDrawing[5334:1a03] time difference was   268
:27:21.281 stepwiseDrawing[5334:1a03] time difference was   270
:27:21.563 stepwiseDrawing[5334:1a03] time difference was   282
:27:21.848 stepwiseDrawing[5334:1a03] time difference was   284
:27:22.126 stepwiseDrawing[5334:1a03] time difference was   278
:27:22.398 stepwiseDrawing[5334:1a03] time difference was   272
:27:22.677 stepwiseDrawing[5334:1a03] time difference was   279
:27:22.970 stepwiseDrawing[5334:1a03] time difference was   293
:27:23.258 stepwiseDrawing[5334:1a03] time difference was   288
:27:23.545 stepwiseDrawing[5334:1a03] time difference was   287
:27:23.834 stepwiseDrawing[5334:1a03] time difference was   289
:27:24.122 stepwiseDrawing[5334:1a03] time difference was   288
:27:24.413 stepwiseDrawing[5334:1a03] time difference was   292
:27:24.708 stepwiseDrawing[5334:1a03] time difference was   295
:27:25.002 stepwiseDrawing[5334:1a03] time difference was   294
:27:25.303 stepwiseDrawing[5334:1a03] time difference was   301
:27:25.585 stepwiseDrawing[5334:1a03] time difference was   282
:27:25.880 stepwiseDrawing[5334:1a03] time difference was   294
:27:26.174 stepwiseDrawing[5334:1a03] time difference was   294
:27:26.470 stepwiseDrawing[5334:1a03] time difference was   296
:27:26.475 stepwiseDrawing[5334:1a03] time difference was     5
:27:26.777 stepwiseDrawing[5334:1a03] time difference was   302
:27:27.077 stepwiseDrawing[5334:1a03] time difference was   299
:27:27.373 stepwiseDrawing[5334:1a03] time difference was   297