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Lazy stat dates #12818

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Lazy stat dates #12818

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ccbc92f
lib: lazy instantiation of fs dates
sciolist May 3, 2017
71b01c6
lint
sciolist May 3, 2017
dcbe6b2
remove blksize from test
sciolist May 22, 2017
1eb7196
lint
sciolist May 22, 2017
61ff138
blocks as well, why not
sciolist May 23, 2017
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71 changes: 67 additions & 4 deletions lib/fs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -196,13 +196,76 @@ function Stats(
this.ino = ino;
this.size = size;
this.blocks = blocks;
this.atime = new Date(atim_msec + 0.5);
this.mtime = new Date(mtim_msec + 0.5);
this.ctime = new Date(ctim_msec + 0.5);
this.birthtime = new Date(birthtim_msec + 0.5);
this._atim_msec = atim_msec;
this._mtim_msec = mtim_msec;
this._ctim_msec = ctim_msec;
this._birthtim_msec = birthtim_msec;
}
fs.Stats = Stats;

Object.defineProperties(Stats.prototype, {
atime: {
configurable: true,
enumerable: true,
get() {
return this._atime !== undefined ?
this._atime :
(this._atime = new Date(this._atim_msec + 0.5));
},
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Can eliminate some code duplication here by having a factory function for the getters... e.g.

function makeGetter(name, src) {
  return function() {
    return this[name] !== undefined ?
      this[name] : (this[name] = new Date(this[src + 0.5));
  };
}

// ...

Object.defineProperties(Stats.prototype, {
  atime: {
    configurable: true,
    enumerable: true,
    get: makeGetter('_atime', '_atim_msec'),
    // etc
  }
});

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Another idea here would be to use another defineProperty within the getter to replace the value once the date is created...

var m = {};
Object.defineProperty(m, 'a', {
  configurable: true,
  enumerable: true,
  get() {
    const val = 1;
    delete this.a;
    Object.defineProperty(this, 'a', { configurable: true, enumerable: true, value: val } );
    return val;
  }
});

The getter is called once, during which time it is deleted, and the static value is set... and will be returned every time after. Should have a slightly better performance profile.

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@TimothyGu suggested that in the previous PR, it wasn't performant enough for the "single access" case - #12607 (comment)

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Ok, that's fine then. I'd still suggest the factory function to avoid the code duplication

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Hey, yeah I have tried these variations.

Unfortunately a single defineProperty is more expensive than 4 date creations, so you'd lose the benefits of the laziness if you need to access even a single date.

this[somevariable] is slow enough compared to this.mtime that the difference becomes pretty significant in a function like stat, that isn't very heavy to begin with. That drops accessing one time-field twice (my test is if (stat.ctime.getTime() !== stat.ctime.getTime()) throw err;) to a 65% improvement over the non-lazy code, down from a 105% improvement if done the ugly way. But I can definitely change to that if it's preferable.. I didn't write it this way because I think it's beautiful. :)

set(value) { return this._atime = value; }
},
mtime: {
configurable: true,
enumerable: true,
get() {
return this._mtime !== undefined ?
this._mtime :
(this._mtime = new Date(this._mtim_msec + 0.5));
},
set(value) { return this._mtime = value; }
},
ctime: {
configurable: true,
enumerable: true,
get() {
return this._ctime !== undefined ?
this._ctime :
(this._ctime = new Date(this._ctim_msec + 0.5));
},
set(value) { return this._ctime = value; }
},
birthtime: {
configurable: true,
enumerable: true,
get() {
return this._birthtime !== undefined ?
this._birthtime :
(this._birthtime = new Date(this._birthtim_msec + 0.5));
},
set(value) { return this._birthtime = value; }
},
});

Stats.prototype.toJSON = function toJSON() {
return {
dev: this.dev,
mode: this.mode,
nlink: this.nlink,
uid: this.uid,
gid: this.gid,
rdev: this.rdev,
blksize: this.blksize,
ino: this.ino,
size: this.size,
blocks: this.blocks,
atime: this.atime,
ctime: this.ctime,
mtime: this.mtime,
birthtime: this.birthtime
};
};


Stats.prototype._checkModeProperty = function(property) {
return ((this.mode & S_IFMT) === property);
};
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22 changes: 22 additions & 0 deletions test/parallel/test-fs-stat.js
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Expand Up @@ -98,5 +98,27 @@ fs.stat(__filename, common.mustCall(function(err, s) {
console.log(`isSymbolicLink: ${JSON.stringify(s.isSymbolicLink())}`);
assert.strictEqual(false, s.isSymbolicLink());

assert.ok(s.atime instanceof Date);
assert.ok(s.mtime instanceof Date);
assert.ok(s.ctime instanceof Date);
assert.ok(s.birthtime instanceof Date);
}));

fs.stat(__filename, common.mustCall(function(err, s) {
const json = JSON.parse(JSON.stringify(s));
const keys = [
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On second thought: either put a comment saying why we exclude blksize
Or put if(!common.isWindows) keys.push('blksize')
Your call but pick one.

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Just found out need to do the same for 'blocks' (undefined on Windows)

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i added an if(!common.isWindows) bit, seems reasonable.

'dev', 'mode', 'nlink', 'uid',
'gid', 'rdev', 'ino',
'size', 'atime', 'mtime',
'ctime', 'birthtime'
];
if (!common.isWindows) {
keys.push('blocks', 'blksize');
}
keys.forEach(function(k) {
assert.ok(
json[k] !== undefined && json[k] !== null,
k + ' should not be null or undefined'
);
});
}));