简单的 iOS 性能监测工具

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由于现在iOS这一块缺少性能测试，导致 app 性能优化方面工作并没有明确的工作目标。所以需要个必要的测试工具来数据化 app 的性能状况。

需要一个工具可以检测 app 的内存占用，CPU使用情况，FPS还有启动时间（可以通过 UIAutomation 来实现）
由于需要检测生产环境下各种友商 app，用于对比性能，所以决定用越狱后tweak来实现性能的检测。

Tweak 的一些实现

（示例代码：Github）

tweak的主要功能是检测app启动后每一秒的内存使用量，CPU使用率，FPS。

内存使用量检测：

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// get current RAM usage
double usedMemory()
{
  task_basic_info_data_t taskInfo;
  mach_msg_type_number_t infoCount = TASK_BASIC_INFO_COUNT;
  kern_return_t kernReturn = task_info(mach_task_self(),
                                       TASK_BASIC_INFO, (task_info_t)&taskInfo, &infoCount);
  if(kernReturn != KERN_SUCCESS) {
      return NSNotFound;
  }

  return taskInfo.resident_size / 1024.0 / 1024.0;
}

CPU使用率检测：

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// get current CPU usage
float cpu_usage()
{
  kern_return_t kr;
  task_info_data_t tinfo;
  mach_msg_type_number_t task_info_count;

  task_info_count = TASK_INFO_MAX;
  kr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)tinfo, &task_info_count);
  if (kr != KERN_SUCCESS) {
      return -1;
  }

  task_basic_info_t basic_info;
  thread_array_t thread_list;
  mach_msg_type_number_t thread_count;

  thread_info_data_t thinfo;
  mach_msg_type_number_t thread_info_count;

  thread_basic_info_t basic_info_th;
  uint32_t stat_thread = 0;

  basic_info = (task_basic_info_t)tinfo;

  kr = task_threads(mach_task_self(), &thread_list, &thread_count);
  if (kr != KERN_SUCCESS) {
      return -1;
  }
  if (thread_count > 0)
      stat_thread += thread_count;

  long tot_sec = 0;
  long tot_usec = 0;
  float tot_cpu = 0;
  int j;

  for (j = 0; j < thread_count; j++)
  {
      thread_info_count = THREAD_INFO_MAX;
      kr = thread_info(thread_list[j], THREAD_BASIC_INFO,
                       (thread_info_t)thinfo, &thread_info_count);
      if (kr != KERN_SUCCESS) {
          return -1;
      }

      basic_info_th = (thread_basic_info_t)thinfo;

      if (!(basic_info_th->flags & TH_FLAGS_IDLE)) {
          tot_sec = tot_sec + basic_info_th->user_time.seconds + basic_info_th->system_time.seconds;
          tot_usec = tot_usec + basic_info_th->system_time.microseconds + basic_info_th->system_time.microseconds;
          tot_cpu = tot_cpu + basic_info_th->cpu_usage / (float)TH_USAGE_SCALE * 100.0;
      }

  }

  kr = vm_deallocate(mach_task_self(), (vm_offset_t)thread_list, thread_count * sizeof(thread_t));
  assert(kr == KERN_SUCCESS);

  return tot_cpu;
}

FPS 监测：

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- (void)displayLinkTick:(CADisplayLink *)displayLink
{
  static CFTimeInterval lastTimeInterval = 0.0;

  CFTimeInterval cuTime = CACurrentMediaTime();
  if (!lastTimeInterval) {
      lastTimeInterval = cuTime;
      return;
  }

  CFTimeInterval newInterval = cuTime - lastTimeInterval;
  lastTimeInterval = cuTime;
  if (newInterval > 1.0 || newInterval <= 0) {
      return;
  }

  currentFPS = round(1.0/ newInterval);
}

由于想要做到通用性，所以选择在 UIApplication 的 delegate 里面的 -application:didFinishLaunchingWithOptions: 来启动检测，由于是 delegate，正常的 Logos 语法没法准确 hook ，于是决定用运行时 Method Swizzling （参考：念茜 Objective-C的hook方案（一）: Method Swizzling ）

自定义IMP用于替换之前的 -application:didFinishLaunchingWithOptions:

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id myDidFinishLaunchingWithOptions_imp(id self, SEL cmd, UIApplication *application, NSDictionary *launchOptions)
{
  BOOL ret = [self myApplication:application didFinishLaunchingWithOptions:launchOptions];
  // remove old log file
  NSString *path = [NSString stringWithFormat:@"/tmp/%@.plist", [NSBundle mainBundle].bundleIdentifier];
  if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
      [[NSFileManager defaultManager] removeItemAtPath:path error:nil];
  }

  // creat a container for recording the log
  logList = [[NSMutableArray alloc] init];

  // get current FPS
  CADisplayLink *displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(displayLinkTick:)];
  [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];

  NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(onTimer) userInfo:nil repeats:YES];
  [timer fire];

  return @(ret);
}

然后在App进入到后台的时候，进行检测记录的文件写入，替换原来的 -applicationDidEnterBackground:

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id myApplicationDidEnterBackground_imp(id self, SEL cmd, UIApplication *application, NSDictionary *launchOptions)
{
  [self myApplicationDidEnterBackground:application];

  [self writeLogsToFile];
}

实现方法替换：

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- (void)setDelegate:(id)delegate
{
  %orig;
  Method method1 = class_getInstanceMethod([delegate class], @selector(application:didFinishLaunchingWithOptions:));
  class_addMethod([delegate class], @selector(myApplication:didFinishLaunchingWithOptions:), (IMP)myDidFinishLaunchingWithOptions_imp, method_getTypeEncoding(method1));
  Method method2 = class_getInstanceMethod([delegate class], @selector(myApplication:didFinishLaunchingWithOptions:));
  method_exchangeImplementations(method1, method2);

  Method method3 = class_getInstanceMethod([delegate class], @selector(applicationDidEnterBackground:));
  class_addMethod([delegate class], @selector(myApplicationDidEnterBackground:), (IMP)myApplicationDidEnterBackground_imp, method_getTypeEncoding(method3));
  Method method4 = class_getInstanceMethod([delegate class], @selector(myApplicationDidEnterBackground:));
  method_exchangeImplementations(method3, method4);
}

Tweak 的使用

和其他的越狱工具大体相当，在 .plist 文件里声明好你想要 hook 的 app（也就是你想要监测的）。利用 Theos 可以把你写好的工具生成一个 dylib ，然后通过已越狱的手机就可以运行了。当然了，如果你要想生成一些报告，还需要在工具中实现。

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