Issue with std::chrono with libc++ in armv7

[koying]

I know this is not a proper bug report but I wanted to report that we found an issue with the following configuration:

NDK: 16b
Arch: armv7
STL: libc++
Code: std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::steady_clock::now().time_since_epoch()).count()

This used to work, and basically gave the same information as

  struct timespec now;
  clock_gettime(CLOCK_MONOTONIC, &now);
  return( ((int64_t)now.tv_sec * 1000000000L) + now.tv_nsec );

Since moving to libc++, it doesn't work as expected anymore.
Replacing the "std::" code with the "clock_gettime" solves the issue.

It's still working fine in aarch64.

Sorry, I didn't actually digged deeper to get to the bottom of it, as I personally wanted to get rid of the std::chrono construct anyways ;)

[alexcohn]

This could be related to #423 (comment). Check if the value is correct for armv7 with target API 21.

[rprichard]

it doesn't work as expected anymore.

How does it fail?

I can't reproduce a problem here. AFAICT, std::chrono::steady_clock is a C++ interface to clock_gettime(CLOCK_MONOTONIC, ...) on Android (android-ndk-r16b/sources/cxx-stl/llvm-libc++/src/chrono.cpp):

steady_clock::time_point
steady_clock::now() _NOEXCEPT
{
    struct timespec tp;
    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
        __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
}

This code works fine:

#include <chrono>

#include <stdint.h>
#include <stdio.h>

unsigned long long time_posix() {
  struct timespec now;
  clock_gettime(CLOCK_MONOTONIC, &now);
  return( ((int64_t)now.tv_sec * 1000000000L) + now.tv_nsec );  
}

unsigned long long time_cxx() {
  return std::chrono::duration_cast<std::chrono::nanoseconds>(
    std::chrono::steady_clock::now().time_since_epoch()).count();
}

int main() {
  printf("%llu\n", time_posix());
  printf("%llu\n", time_cxx());
}

time_posix and time_cxx output roughly the same value.

NDK Version: r16b
Build system: ndk-build
Host OS: Linux
Compiler: Clang (w/ APP_CPPFLAGS := -std=c++11)
ABI: armeabi-v7a
STL: c++_static
NDK API level: 21
Device API level: 26

[DanAlbert]

Closing since we couldn't repro. Will reopen if we get a failing test case.