How does getCurrentTime work under GHCJS?

Question

Under GHCJS, how does getCurrentTime work? In the time library itself, this is implemented using the FFI, calling out to functions provided by the operating system. However, there aren't any lines in time that start with:

foreign import javascript ...

I've checked the shims repository that GHCJS using to patch libraries. It patches the timezone getting function but has no mention of getCurrentTime. The only thing I found that was remotely close was in ghcjs-boot, where old-time is patched with an:

#ifdef ghcjs_HOST_OS
type CTimeVal = ()
type CTimeZone = ()
...
foreign import ccall unsafe "HsTime.h __hscore_gettimeofday"
    gettimeofday :: Ptr CTimeVal -> Ptr CTimeZone -> IO CInt
...

But there are two problems with this. One is that it's not the right library (old-time instead of time). The other is that it's still using the C FFI. I don't understand how the using the C FFI can work when you are compiling with GHCJS.

So, where does getCurrentTime get shimmed in for GHCJS?

In response to the comment about grepping ghcjs source, if I search for getTime (which I believe would be the javascript function used) in GHCJS's source, I get basically nothing. However, by grepping an all.js file produced by GHCJS for a project that uses getCurrentTime, I get this:

ag '\bgetTime\b' all.js
20948:  h$log((("elapsed time: " + (h$RTS_597.getTime() - h$RTS_595.getTime())) + "ms"));
22863:                var atime = goog.math.Long.fromNumber(fs.atime.getTime());
22864:                var mtime = goog.math.Long.fromNumber(fs.mtime.getTime());
22865:                var ctime = goog.math.Long.fromNumber(fs.ctime.getTime());

The latter three are from some kind of filesystem shim.

I found this in the generated javascript:

function h$gettimeofday(tv_v,tv_o,tz_v,tz_o) {
  var now = Date.now();
  tv_v.dv.setInt32(tv_o, (now / 1000)|0, true);
  tv_v.dv.setInt32(tv_o + 4, ((now % 1000) * 1000)|0, true);
  if(tv_v.len >= tv_o + 12) {
    tv_v.dv.setInt32(tv_o + 8, ((now % 1000) * 1000)|0, true);
  }
  return 0;
}

But the question of how this got linked in remains.

Could you `grep -r` the GHCJS source searching for the JS time primitive? — dfeuer, Sep 06 '16 at 17:14
@dfeuer I've added the results. I think that it might not be `getTime` that gets used by GHCJS. Although that seems that the obvious choice for POSIX time. — Andrew Thaddeus Martin, Sep 06 '16 at 17:34
It looks more like a primitive than something "linked in", so you might check the code generator. That `h$` could even be a special pattern it looks for. I could be wrong though! — dfeuer, Sep 06 '16 at 18:17
I discovered `h$gettimeofday` in shims `src/environment.js` https://github.com/ghcjs/shims/blob/master/src/environment.js#L243 — Steven Shaw, Sep 07 '16 at 03:46

How does getCurrentTime work under GHCJS?

0 Answers0