How can I get a precise time for example in milliseconds in Objective-C

Question

Is there an easy way to get a time very precisely    I need to calculate some delays between method calls  More specifically  I want to calculate the speed of scrolling in an UIScrollView

User · Answer

Please do not use NSDate  CFAbsoluteTimeGetCurrent  or gettimeofday to measure elapsed time  These all depend on the system clock  which can change at any time due to many different reasons  such as network time sync  NTP  updating the clock  happens often to adjust for drift   DST adjustments  leap seconds  and so on   This means that if you re measuring your download or upload speed  you will get sudden spikes or drops in your numbers that don t correlate with what actually happened  your performance tests will have weird incorrect outliers  and your manual timers will trigger after incorrect durations  Time might even go backwards  and you end up with negative deltas  and you can end up with infinite recursion or dead code  yeah  I ve done both of these    Use mach absolute time  It measures real seconds since the kernel was booted  It is monotonically increasing  will never go backwards   and is unaffected by date and time settings  Since it s a pain to work with  here s a simple wrapper that gives you NSTimeIntervals      LBClock h  interface LBClock   NSObject    instancetype sharedClock     since device boot or something  Monotonically increasing  unaffected by date and time settings -  NSTimeInterval absoluteTime   -  NSTimeInterval machAbsoluteToTimeInterval  uint64 t machAbsolute   end     LBClock m  include  lt mach mach h gt   include  lt mach mach time h gt    implementation LBClock       mach timebase info data t  clock timebase        instancetype sharedClock       static LBClock  g      static dispatch once t onceToken      dispatch once  amp onceToken             g    LBClock new               return g     -  id init       if   self    super init            return nil      mach timebase info  amp  clock timebase       return self     -  NSTimeInterval machAbsoluteToTimeInterval  uint64 t machAbsolute       uint64 t nanos    machAbsolute    clock timebase numer     clock timebase denom       return nanos 1 0e9     -  NSTimeInterval absoluteTime       uint64 t machtime   mach absolute time        return  self machAbsoluteToTimeInterval machtime      end

User · Answer

Also  here is how to calculate a 64-bit NSNumber initialized with the Unix epoch in milliseconds  in case that is how you want to store it in CoreData  I needed this for my app which interacts with a system that stores dates this way        NSNumber   longUnixEpoch         return  NSNumber numberWithLongLong   NSDate date  timeIntervalSince1970    1000

User · Answer

CFAbsoluteTimeGetCurrent   returns the absolute time as a double value  but I don t know what its precision is -- it might only update every dozen milliseconds  or it might update every microsecond  I don t know

User · Answer

You can get current time in milliseconds since January 1st  1970 using an NSDate   -  double currentTimeInMilliseconds       NSDate  date    NSDate date       return  date timeIntervalSince1970  1000

User · Answer

mach absolute time   can be used to get precise measurements  See http   developer apple com qa qa2004 qa1398 html Also available is CACurrentMediaTime    which is essentially the same thing but with an easier-to-use interface   Note  This answer was written in 2009  See Pavel Alexeev s answer for the simpler POSIX clock gettime   interfaces available in newer versions of macOS and iOS

User · Answer

define CTTimeStart   NSDate     date    NSDate date   define CTTimeEnd MSG  NSLog MSG    g     date timeIntervalSinceNow  -1    Usage   CTTimeStart        CTTimeEnd   that was a long time       Output   2013-08-23 15 34 39 558 App-Dev 21229 907  that was a long time   0023

User · Answer

I would NOT use mach absolute time   because it queries a combination of the kernel and the processor for an absolute time using ticks  probably an uptime    What I would use    CFAbsoluteTimeGetCurrent      This function is optimized to correct the difference in the iOS and OSX software and hardware   Something Geekier  The quotient of a difference in mach absolute time   and AFAbsoluteTimeGetCurrent   is always around 24000011 154871  Here is a log of my app   Please note that final result time is a difference in CFAbsoluteTimeGetCurrent   s   2012-03-19 21 46 35 609 Rest Counter 3776 707  First Time  353900795 609040  2012-03-19 21 46 36 360 Rest Counter 3776 707  Second Time  353900796 360177  2012-03-19 21 46 36 361 Rest Counter 3776 707  Final Result Time  difference   0 751137  2012-03-19 21 46 36 363 Rest Counter 3776 707  Mach absolute time  18027372  2012-03-19 21 46 36 365 Rest Counter 3776 707  Mach absolute time final time  24000113 153295  2012-03-19 21 46 36 367 Rest Counter 3776 707  -----------------------------------------------------  2012-03-19 21 46 43 074 Rest Counter 3776 707  First Time  353900803 074637  2012-03-19 21 46 43 170 Rest Counter 3776 707  Second Time  353900803 170256  2012-03-19 21 46 43 172 Rest Counter 3776 707  Final Result Time  difference   0 095619  2012-03-19 21 46 43 173 Rest Counter 3776 707  Mach absolute time  2294833  2012-03-19 21 46 43 175 Rest Counter 3776 707  Mach absolute time final time  23999753 727777  2012-03-19 21 46 43 177 Rest Counter 3776 707  -----------------------------------------------------  2012-03-19 21 46 46 499 Rest Counter 3776 707  First Time  353900806 499199  2012-03-19 21 46 55 017 Rest Counter 3776 707  Second Time  353900815 016985  2012-03-19 21 46 55 018 Rest Counter 3776 707  Final Result Time  difference   8 517786  2012-03-19 21 46 55 020 Rest Counter 3776 707  Mach absolute time  204426836  2012-03-19 21 46 55 022 Rest Counter 3776 707  Mach absolute time final time  23999996 639500  2012-03-19 21 46 55 024 Rest Counter 3776 707  -----------------------------------------------------

User · Answer

Functions based on mach absolute time are good for short measurements  But for long measurements important caveat is that they stop ticking while device is asleep     There is a function to get time since boot  It doesn t stop while sleeping  Also  gettimeofday is not monotonic  but in my experiments I ve always see that boot time changes when system time changes  so I think it should work fine   func timeSinceBoot   - gt  TimeInterval       var bootTime   timeval       var currentTime   timeval       var timeZone   timezone        let mib   UnsafeMutablePointer lt Int32 gt  allocate capacity  2      mib 0    CTL KERN     mib 1    KERN BOOTTIME     var size   MemoryLayout size ofValue  bootTime       var timeSinceBoot   0 0      gettimeofday  amp currentTime   amp timeZone       if sysctl mib  2   amp bootTime   amp size  nil  0     -1  amp  amp  bootTime tv sec    0           timeSinceBoot   Double currentTime tv sec - bootTime tv sec          timeSinceBoot    Double currentTime tv usec - bootTime tv usec    1000000 0           return timeSinceBoot     And since iOS 10 and macOS 10 12 we can use CLOCK MONOTONIC   if  available OSX 10 12           var uptime   timespec       if clock gettime CLOCK MONOTONIC RAW   amp uptime     0           return Double uptime tv sec    Double uptime tv nsec    1000000000 0           To sum it up    Date timeIntervalSinceReferenceDate     changes when system time changes  not monotonic CFAbsoluteTimeGetCurrent       not monotonic  may go backward CACurrentMediaTime       stops ticking when device is asleep timeSinceBoot       doesn t sleep  but might be not monotonic CLOCK MONOTONIC     doesn t sleep  monotonic  supported since iOS 10

User · Answer

I know this is an old one but even I found myself wandering past it again  so I thought I d submit my own option here   Best bet is to check out my blog post on this  Timing things in Objective-C  A stopwatch  Basically  I wrote a class that does stop watching in a very basic way but is encapsulated so that you only need to do the following    MMStopwatchARC start   My Timer       your work here      MMStopwatchARC stop   My Timer      And you end up with   MyApp 4090 15203   - gt  Stopwatch   My Timer  runtime   0 029    in the log     Again  check out my post for a little more or download it here  MMStopwatch zip

User · Answer

For those we need the Swift version of the answer of  Jeff Thompson       Get a current time for where you want to start measuring from var date   NSDate       do work        Find elapsed time and convert to milliseconds    Use  -  modifier to conversion since receiver is earlier than now var timePassed ms  Double   date timeIntervalSinceNow   -1000 0   I hope this help you

User · Answer

NSDate and the timeIntervalSince  methods will return a NSTimeInterval which is a double with sub-millisecond accuracy  NSTimeInterval is in seconds  but it uses the double to give you greater precision   In order to calculate millisecond time accuracy  you can do      Get a current time for where you want to start measuring from NSDate  date    NSDate date       do work        Find elapsed time and convert to milliseconds    Use  -  modifier to conversion since receiver is earlier than now double timePassed ms    date timeIntervalSinceNow    -1000 0    Documentation on timeIntervalSinceNow   There are many other ways to calculate this interval using NSDate  and I would recommend looking at the class documentation for NSDate which is found in NSDate Class Reference

[iphone] How can I get a precise time, for example in milliseconds in Objective-C?

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