iOS时间差值计算方法

• 开发中在很多情况下需要测试某一个代码块执行的时间,以便提供更好的优化方案,以下提供了几种时间差值计算的方案.

dispatch_benchmark

• dispatch_benchmark 是苹果GCD内部API,能直接返回某一个代码块执行多次后的平均每次执行时间,返回时间单位是ns.
• 使用方法如下:

1. 需要提前声明,否则会报错,提示私有API无法直接使用.

// 因为是私有api 所以需要声明一下 count代表block执行的次数
extern uint64_t dispatch_benchmark(size_t count, void(^bock)(void));

2. 声明后可以直接使用,使用方法如下

  // block执行次数
     size_t count = 300;
    size_t signalCount = 1000;
    //benchmarkTime 为执行该block count 次后平均每一次的时间,单位ns
    // block内部的代码会循环执行count * signalCount 次
   uint64_t benchmarkTime = dispatch_benchmark(count, ^{
        for (int j = 0; j < 1000; j++) {
            @autoreleasepool {
                NSMutableArray* array = [NSMutableArray array];
                for (int i = 0; i < signalCount; ++i) {
                    [array addObject:@1];
                }
            }
        }
    });
    // 单位ns 
    /*
     1秒=1000毫秒(ms),1毫秒=1／1000秒(s)；
     1秒=1000000 微秒(μs),1微秒=1／1000000秒(s)；
     1秒=1000000000 纳秒(ns),1纳秒=1／1000000000秒(s)；
     1秒=1000000000000皮秒 1皮秒==1/1000000000000秒.
     */
   // benchmark time is = 29739487, is 0.029739 secound
    NSLog(@"benchmark time is = %llu, is %f secound",benchmarkTime,benchmarkTime*1.0/1000000000);

CACurrentMediaTime

/* Returns the current CoreAnimation absolute time. This is the result of
* calling mach_absolute_time () and converting the units to seconds. */

• CACurrentMediaTime是通过获取coreAnimation层的绝对时间进行计算,单位是s.
• 使用方法如下:

 CFTimeInterval startTimeInterval = CACurrentMediaTime();
   for (int i = 0; i < 1000; ++i) {
        @autoreleasepool{
            NSMutableArray* array = [NSMutableArray array];
            for (int i = 0; i < 1000; ++i) {
                [array addObject:@1];
            }
        }
    }
    CFTimeInterval endTimeInterval = CACurrentMediaTime();
    //endTimeInterval - startTimeInterval = 0.028688
    NSLog(@"endTimeInterval - startTimeInterval = %f",endTimeInterval - startTimeInterval);

NSDate获取时间

• 通过NSDate 的属性timeIntervalSinceReferenceDate 获取到参考日期以来的间隔,然后计算两个间隔之间的差值.单位是s.

NSDate* date = [[NSDate alloc] init];
    
    // 参考日期以来的间隔
    NSTimeInterval startTime = [date timeIntervalSinceReferenceDate];
     for (int i = 0; i < 1000; ++i) {
        @autoreleasepool{
            NSMutableArray* array = [NSMutableArray array];
            for (int i = 0; i < 1000; ++i) {
                [array addObject:@1];
            }
        }
    }
   NSTimeInterval endTime = [[NSDate date] timeIntervalSinceReferenceDate];
    // endTime - startTime is = 0.029718 单位s
    NSLog(@"endTime - startTime is = %f",endTime - startTime);

CFAbsoluteTime

• 通过CFAbsoluteTimeGetCurrent获取时间.
• API说明
  /* absolute time is the time interval since the reference date /
  / the reference date (epoch) is 00:00:00 1 January 2001. */
  你会发现 其实和NSDate 原理是一样的,与参考时间进行计算.
  具体使用如下:

 /* absolute time is the time interval since the reference date */
    /* the reference date (epoch) is 00:00:00 1 January 2001. */
    // 你会发现 其实和NSDate 原理是一样的,与参考时间进行计算
    CFAbsoluteTime absoluteTimeStart =  CFAbsoluteTimeGetCurrent();
  for (int i = 0; i < 1000; ++i) {
        @autoreleasepool{
            NSMutableArray* array = [NSMutableArray array];
            for (int i = 0; i < 1000; ++i) {
                [array addObject:@1];
            }
        }
    }
    CFAbsoluteTime absoluteTimeEnd = CFAbsoluteTimeGetCurrent();
    // absoluteTimeEnd - absoluteTimeStart = 0.028272  单位s
    NSLog(@"absoluteTimeEnd - absoluteTimeStart = %f",absoluteTimeEnd - absoluteTimeStart);

clock_t

• 通过clock获取时钟时间,同样适用于c++,单位us
• 使用方法:

  clock_t startTime = clock();
    for (int i = 0; i < 1000; ++i) {
        @autoreleasepool{
            NSMutableArray* array = [NSMutableArray array];
            for (int i = 0; i < 1000; ++i) {
                [array addObject:@1];
            }
        }
    }
    clock_t endTime = clock();
  //endTime - startTime is = 28534, is 0.028534 second
    NSLog(@"endTime - startTime is = %lu, is %f second",endTime - startTime,(endTime - startTime)*1.0/CLOCKS_PER_SEC);