是否有一种方法可以确定一个方法需要执行多少时间(以毫秒为单位)?
当前回答
下面是我使用的两个单行宏:
#define TICK NSDate *startTime = [NSDate date]
#define TOCK NSLog(@"Time: %f", -[startTime timeIntervalSinceNow])
像这样使用它:
TICK;
/* ... Do Some Work Here ... */
TOCK;
其他回答
一个在Swift 4中使用mach_absolute_time()的细粒度计时的例子:
let start = mach_absolute_time()
// do something
let elapsedMTU = mach_absolute_time() - start
var timebase = mach_timebase_info()
if mach_timebase_info(&timebase) == 0 {
let elapsed = Double(elapsedMTU) * Double(timebase.numer) / Double(timebase.denom)
print("render took \(elapsed)")
}
else {
print("timebase error")
}
我使用非常少的,一页的类实现,灵感来自这篇博客文章的代码:
#import <mach/mach_time.h>
@interface DBGStopwatch : NSObject
+ (void)start:(NSString *)name;
+ (void)stop:(NSString *)name;
@end
@implementation DBGStopwatch
+ (NSMutableDictionary *)watches {
static NSMutableDictionary *Watches = nil;
static dispatch_once_t OnceToken;
dispatch_once(&OnceToken, ^{
Watches = @{}.mutableCopy;
});
return Watches;
}
+ (double)secondsFromMachTime:(uint64_t)time {
mach_timebase_info_data_t timebase;
mach_timebase_info(&timebase);
return (double)time * (double)timebase.numer /
(double)timebase.denom / 1e9;
}
+ (void)start:(NSString *)name {
uint64_t begin = mach_absolute_time();
self.watches[name] = @(begin);
}
+ (void)stop:(NSString *)name {
uint64_t end = mach_absolute_time();
uint64_t begin = [self.watches[name] unsignedLongLongValue];
DDLogInfo(@"Time taken for %@ %g s",
name, [self secondsFromMachTime:(end - begin)]);
[self.watches removeObjectForKey:name];
}
@end
它的用法很简单:
调用[DBGStopwatch start:@"slow-operation"];一开始 然后[DBGStopwatch stop:@"slow-operation"];做完之后,才能得到时间
NSDate *methodStart = [NSDate date];
/* ... Do whatever you need to do ... */
NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);
迅速:
let methodStart = NSDate()
/* ... Do whatever you need to do ... */
let methodFinish = NSDate()
let executionTime = methodFinish.timeIntervalSinceDate(methodStart)
print("Execution time: \(executionTime)")
Swift3:
let methodStart = Date()
/* ... Do whatever you need to do ... */
let methodFinish = Date()
let executionTime = methodFinish.timeIntervalSince(methodStart)
print("Execution time: \(executionTime)")
易于使用,具有亚毫秒精度。
对于OS X上的细粒度计时,您应该使用在<mach/mach_time.h>中声明的mach_absolute_time():
#include <mach/mach_time.h>
#include <stdint.h>
// Do some stuff to setup for timing
const uint64_t startTime = mach_absolute_time();
// Do some stuff that you want to time
const uint64_t endTime = mach_absolute_time();
// Time elapsed in Mach time units.
const uint64_t elapsedMTU = endTime - startTime;
// Get information for converting from MTU to nanoseconds
mach_timebase_info_data_t info;
if (mach_timebase_info(&info))
handleErrorConditionIfYoureBeingCareful();
// Get elapsed time in nanoseconds:
const double elapsedNS = (double)elapsedMTU * (double)info.numer / (double)info.denom;
当然,关于细粒度度量的通常警告也适用;您可能最好多次调用测试中的例程,并求平均值/取最小值/一些其他形式的处理。
此外,请注意,您可能会发现使用Shark等工具对应用程序运行进行概要分析更有用。这不会为您提供确切的时间信息,但它会告诉您应用程序的时间在哪里花费了多少百分比,这通常更有用(但并不总是如此)。
mach_absolute_time()有一个方便的包装器——它是来自CoreAnimation框架的CACurrentMediaTime()函数。
与NSDate或CFAbsoluteTimeGetCurrent()偏移量不同, mach_absolute_time()和CACurrentMediaTime()基于 主机内部时钟,精确,单原子测量,且不受影响 外部时间参考的更改,例如由时间引起的更改 区域、夏令时或闰秒。
ObjC
#import <QuartzCore/QuartzCore.h>
CFTimeInterval startTime = CACurrentMediaTime();
// Do your stuff here
CFTimeInterval endTime = CACurrentMediaTime();
NSLog(@"Total Runtime: %g s", endTime - startTime);
斯威夫特
import QuartzCore
let startTime = CACurrentMediaTime()
// Do your stuff here
let endTime = CACurrentMediaTime()
print("Total Runtime: \(endTime - startTime) s")
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