Android NDK chrono epoch is not correct (std::chrono::high_resolution_clock)

Android NDK chrono Epoch Inconsistency

This article explores the issue of incorrect epoch values when using the std::chrono::high_resolution_clock in Android NDK applications.

Understanding the Problem

The std::chrono::high_resolution_clock is intended to provide the most precise time measurement available on a system. However, on Android NDK, it often returns an epoch value that differs significantly from the expected value.

Cause of the Inconsistency

• The Android NDK utilizes a custom implementation of the C++ standard library.
• This implementation may not accurately reflect the system’s time source.
• The epoch used by the NDK’s high_resolution_clock may not align with the Unix epoch (January 1, 1970).

Impact of the Inconsistency

The inaccurate epoch can lead to problems in scenarios involving:

• Time-sensitive operations: Calculations involving time differences may produce incorrect results.
• Data logging and analysis: Timestamps may not be consistent with other systems.
• Synchronization and communication: Time-based synchronization mechanisms can be affected.

Workarounds and Solutions

1. Using the System Clock

The std::chrono::system_clock provides a more reliable time source in the Android NDK. It is synchronized with the system time, ensuring consistency with other applications.

#include <chrono>

auto now = std::chrono::system_clock::now();
auto time_since_epoch = now.time_since_epoch();
auto milliseconds = std::chrono::duration_cast<std::chrono::milliseconds>(time_since_epoch);

2. Implementing Custom Epoch Handling

If precise timing is crucial, consider implementing custom epoch handling to adjust the high_resolution_clock values.

#include <chrono>
#include <ctime>

// Get the current time in seconds since the Unix epoch
time_t current_time = time(nullptr);

// Get the time since the epoch as reported by high_resolution_clock
auto high_res_time = std::chrono::high_resolution_clock::now();

// Calculate the difference between the two epochs
auto epoch_offset = std::chrono::duration_cast<std::chrono::milliseconds>(high_res_time.time_since_epoch() - std::chrono::duration_cast<std::chrono::milliseconds>(current_time * 1000));

// Adjust the high_resolution_clock time to reflect the Unix epoch
auto adjusted_time = high_res_time - epoch_offset;

3. Using a Third-Party Library

Libraries like Boost.Date_Time offer reliable and cross-platform time handling capabilities.

Conclusion

The Android NDK’s std::chrono::high_resolution_clock may provide an inaccurate epoch value, impacting time-sensitive operations and data integrity. Utilize alternative time sources like std::chrono::system_clock, implement custom epoch handling, or leverage third-party libraries to ensure reliable time measurement in your Android NDK projects.