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Safari web worker shows incorrect steady_clock values #4929

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isaacl opened this issue Feb 7, 2017 · 5 comments
Closed

Safari web worker shows incorrect steady_clock values #4929

isaacl opened this issue Feb 7, 2017 · 5 comments
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@isaacl
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isaacl commented Feb 7, 2017

steady_clock prints incorrect values in safari. chrono::system_clock does not have this issue.

Safari (wrong)

Main: elapsed 1
Worker: elapsed -71000

Chrome / Firefox:

Main: elapsed 4
Worker: elapsed 4

---Code Below---

$ cat simpleEm.cpp

#include <chrono>
#include <iostream>
#include <stdio.h>

typedef std::chrono::milliseconds::rep TimePoint;

inline TimePoint now() {
  return std::chrono::duration_cast<std::chrono::milliseconds>
        (std::chrono::steady_clock::now().time_since_epoch()).count();
}

int main() {
  TimePoint start = now();
  std::cout << "elapsed " << now() - start << "\n";
  return 0;
}

$ cat pre.js

var Module = {
  print: function(e) { postMessage(e); }
};


$ cat index.html

<head>
    <script>
      postMessage = function(msg) {
          console.log("Main: " + msg);
      }
    </script>
    <script src="a.out.js"></script>
    <script>
        var worker = new Worker('a.out.js');

        worker.addEventListener('message', function(e) {
              console.log("Worker: " + e.data);
          }, false);

        worker.postMessage('');
      </script>
</head>

build with: em++ -std=c++11 --pre-js pre.js -O3 simpleEm.cpp

emscripten 1.37.1
OS X 10.11.6
Safari 9.1.3
@isaacl isaacl mentioned this issue Feb 7, 2017
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@kripken
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kripken commented Feb 7, 2017

Hmm, this could be a safari bug? I don't have a mac to test, but that's what I'd guess. Might be best to reduce this to a small testcase using the relevant APIs and file a bug for WebKit.

@isaacl
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isaacl commented Feb 9, 2017

Hmm, this could be a safari bug?

Possibly. But chrono::system_clock works fine. So I suspect emscripten_get_now_is_monotonic() is returning false.

@gauravdewan007
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High resolution clock(Performance.now) is not supported in Safari and Edge WebWorker. See the thread:
https://groups.google.com/forum/#!msg/emscripten-discuss/6sKiD-EyMxQ/CiHMqLBZAgAJ
There is simple polyfill work-around.

@isaacl
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isaacl commented Feb 15, 2017

Is this an emscripten bug? (using the wrong time source)

@stale
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stale bot commented Aug 30, 2019

This issue has been automatically marked as stale because there has been no activity in the past 2 years. It will be closed automatically if no further activity occurs in the next 7 days. Feel free to re-open at any time if this issue is still relevant.

@stale stale bot added the wontfix label Aug 30, 2019
@stale stale bot closed this as completed Sep 6, 2019
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@kripken @isaacl @gauravdewan007