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
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
其他回答
我用这个:
clock_t start, end;
double elapsed;
start = clock();
//Start code to time
//End code to time
end = clock();
elapsed = ((double) (end - start)) / CLOCKS_PER_SEC;
NSLog(@"Time: %f",elapsed);
但我不确定iPhone上的CLOCKS_PER_SEC。你还是别打了吧。
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。
许多答案很奇怪,并没有真正以毫秒为单位给出结果(而是以秒或其他单位):
这里是我用来获得MS(毫秒):
迅速:
let startTime = NSDate().timeIntervalSince1970 * 1000
// your Swift code
let endTimeMinusStartTime = NSDate().timeIntervalSince1970 * 1000 - startTime
print("time code execution \(endTimeMinStartTime) ms")
objective - c:
double startTime = [[NSDate date] timeIntervalSince1970] * 1000.0;
// your Objective-C code
double endTimeMinusStartTime = [[NSDate date] timeIntervalSince1970] * 1000.0 - startTime;
printf("time code execution %f ms\n", endTimeMinusStartTime );
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")
}
我在我的utils库中使用这个(Swift 4.2):
public class PrintTimer {
let start = Date()
let name: String
public init(file: String=#file, line: Int=#line, function: String=#function, name: String?=nil) {
let file = file.split(separator: "/").last!
self.name = name ?? "\(file):\(line) - \(function)"
}
public func done() {
let end = Date()
print("\(self.name) took \((end.timeIntervalSinceReferenceDate - self.start.timeIntervalSinceReferenceDate).roundToSigFigs(5)) s.")
}
}
…然后调用如下方法:
func myFunctionCall() {
let timer = PrintTimer()
// ...
timer.done()
}
…运行后在控制台中看起来是这样的:
MyFile.swift:225 - myFunctionCall() took 1.8623 s.
虽然不像上面的TICK/TOCK那样简洁,但它足以清楚地看到它在做什么,并自动包括正在计时的内容(通过文件、方法开头的行和函数名)。显然,如果我想要更多的细节(例如,如果我不只是计时一个方法调用,因为是通常的情况下,而是在该方法内计时块),我可以在PrintTimer init上添加“name="Foo""参数来命名它除了默认值之外的东西。
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