>
> To reproduce, on emscripten 1.36.5 (incoming branch)
>
(1) here is simple test case (c.cpp)
#include <chrono>
#include <iostream>
int
main()
{
std::cout << "before" << std::endl;
auto now = std::chrono::high_resolution_clock::now();
std::cout << "after" << std::endl;
return 0;
}
(2) Compile it using
em++ c.cpp -o c.html
(3) In generated c.js, add following line as first line (To simulate
Safari/IE/Edge webworker environment restriction on FF/Chrome)
performance={};
Output:
Only before is printed followed by exception (some implementations of
boost::chrono::steady_clock::now may throw exception; but here we are using
std::chrono )
Reason:
*__ZNSt3__26chrono12steady_clock3nowEv *(_std::__2::chrono::
*steady_clock::now(*)) calls (via invoke_ii) *_clock_gettime(*clk_id
=1,tp)
*_clock_gettime *calls*_emscripten_get_now_is_monotonic* which return false
*_clock_gettime* then sets error number and return -1.
*__ZNSt3__26chrono12steady_clock3nowEv *on seeing this error throws if
exceptions are enabled *or *continue (with unexpected time value) if
exceptions are disabled.
YES, _emscripten_get_now checks if performance exists and then uses a
fallback but it is not called due to monotonicity test failure
Other consideration:
As mentioned in comment, Date.now does not guarantee monotonicty and it may
be issue depending on some implementation. An answer here indicate how
Date.now can be forced to be monotonic:
http://stackoverflow.com/questions/7272395/monotonically-increasing-time-in-javascript
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