iOS 准确获取app进程启动时间点

debug环境下打印启动耗时环境变量设置

EditSchema -> Run -> Arguments -> Environment Variables添加
DYLD_PRINT_STATISTICS和DYLD_PRINT_STATISTICS_DETAILS值均为1

其中DYLD_PRINT_STATISTICS打印信息如下：

Total pre-main time: 203.41 milliseconds (100.0%)
         dylib loading time: 164.62 milliseconds (80.9%)
        rebase/binding time: 126687488.9 seconds (48910103.9%)
            ObjC setup time:  12.02 milliseconds (5.9%)
           initializer time:  56.09 milliseconds (27.5%)
           slowest intializers :
             libSystem.B.dylib :   2.42 milliseconds (1.1%)
   libBacktraceRecording.dylib :   4.68 milliseconds (2.3%)
    libMainThreadChecker.dylib :  33.34 milliseconds (16.3%)
                    ShadowDemo :  11.59 milliseconds (5.7%)

DYLD_PRINT_STATISTICS_DETAILS输出如下：

  total time: 8.1 seconds (100.0%)
  total images loaded:  358 (351 from dyld shared cache)
  total segments mapped: 21, into 383 pages
  total images loading time: 7.8 seconds (95.4%)
  total load time in ObjC:  12.02 milliseconds (0.1%)
  total debugger pause time: 7.6 seconds (93.4%)
  total dtrace DOF registration time:   0.00 milliseconds (0.0%)
  total rebase fixups:  45,504
  total rebase fixups time:   6.99 milliseconds (0.0%)
  total binding fixups: 533,200
  total binding fixups time: 296.49 milliseconds (3.6%)
  total weak binding fixups time:   0.93 milliseconds (0.0%)
  total redo shared cached bindings time: 333.74 milliseconds (4.0%)
  total bindings lazily fixed up: 0 of 0
  total time in initializers and ObjC +load:  56.09 milliseconds (0.6%)
                         libSystem.B.dylib :   2.42 milliseconds (0.0%)
                libMainThreadChecker.dylib :  33.34 milliseconds (0.4%)
                                ShadowDemo :  11.59 milliseconds (0.1%)
total symbol trie searches:    1243688
total symbol table binary searches:    0
total images defining weak symbols:  37
total images using weak symbols:  92

开发阶段只具备参考意义，并不能准确反映线上的情况。

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获取进程创建的时间

#import 
#import 

static CFAbsoluteTime __startProcessTime = 0.f; // 进程创建时间
void processStartTime() {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        struct kinfo_proc kProcInfo;
        int cmd[4] = {CTL_KERN, KERN_PROC, KERN_PROC_PID, [[NSProcessInfo processInfo] processIdentifier]};
        size_t size = sizeof(kProcInfo);
        
        __startProcessTime = 0.f;
        if (sysctl(cmd, sizeof(cmd)/sizeof(*cmd), &kProcInfo, &size, NULL, 0) == 0) {
            NSUInteger startTime = kProcInfo.kp_proc.p_un.__p_starttime.tv_sec * 1000.0 + kProcInfo.kp_proc.p_un.__p_starttime.tv_usec / 1000.0;
            
            /// 处理成相对于2001/01/01 00:00:00的绝对时间戳，以便与CFAbsoluteTimeGetCurrent()时间戳相对应
            NSCalendar * calendar = [NSCalendar currentCalendar];
            calendar.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
            NSDate *date = [calendar dateWithEra:1 year:2001 month:1 day:1 hour:0 minute:0 second:0 nanosecond:0];
            NSTimeInterval interval = [date timeIntervalSince1970];
            __startProcessTime = startTime - interval * 1000;
        }
    });
}

其他方案，诸如将某个+load的调用时间作为启动的时间点，或者注入一个动态库，在动态库中某个时机记录一个时间作为起始时间都不够精确。