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chore(Scope): short-circuit after dirty-checking last dirty watcher
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Stop dirty-checking during $digest after the last dirty watcher has been re-checked.

This prevents unneeded re-checking of the remaining watchers (They were already
checked in the previous iteration), bringing a substantial performance improvement
to the average case run time of $digest.

Closes #5272
Closes #5287
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@kseamon @IgorMinar
kseamon authored and IgorMinar committed Dec 5, 2013
1 parent 09648e4 commit d070450
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Showing 2 changed files with 112 additions and 17 deletions.
53 changes: 36 additions & 17 deletions src/ng/rootScope.js
View file
Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,7 @@
function $RootScopeProvider(){
var TTL = 10;
var $rootScopeMinErr = minErr('$rootScope');
var lastDirtyWatch = null;

this.digestTtl = function(value) {
if (arguments.length) {
Expand Down Expand Up @@ -325,6 +326,8 @@ function $RootScopeProvider(){
eq: !!objectEquality
};

lastDirtyWatch = null;

// in the case user pass string, we need to compile it, do we really need this ?
if (!isFunction(listener)) {
var listenFn = compileToFn(listener || noop, 'listener');
Expand Down Expand Up @@ -553,6 +556,8 @@ function $RootScopeProvider(){

beginPhase('$digest');

lastDirtyWatch = null;

do { // "while dirty" loop
dirty = false;
current = target;
Expand All @@ -565,8 +570,10 @@ function $RootScopeProvider(){
clearPhase();
$exceptionHandler(e);
}
lastDirtyWatch = null;
}

traverseScopesLoop:
do { // "traverse the scopes" loop
if ((watchers = current.$$watchers)) {
// process our watches
Expand All @@ -576,22 +583,30 @@ function $RootScopeProvider(){
watch = watchers[length];
// Most common watches are on primitives, in which case we can short
// circuit it with === operator, only when === fails do we use .equals
if (watch && (value = watch.get(current)) !== (last = watch.last) &&
!(watch.eq
? equals(value, last)
: (typeof value == 'number' && typeof last == 'number'
&& isNaN(value) && isNaN(last)))) {
dirty = true;
watch.last = watch.eq ? copy(value) : value;
watch.fn(value, ((last === initWatchVal) ? value : last), current);
if (ttl < 5) {
logIdx = 4 - ttl;
if (!watchLog[logIdx]) watchLog[logIdx] = [];
logMsg = (isFunction(watch.exp))
? 'fn: ' + (watch.exp.name || watch.exp.toString())
: watch.exp;
logMsg += '; newVal: ' + toJson(value) + '; oldVal: ' + toJson(last);
watchLog[logIdx].push(logMsg);
if (watch) {
if ((value = watch.get(current)) !== (last = watch.last) &&
!(watch.eq
? equals(value, last)
: (typeof value == 'number' && typeof last == 'number'
&& isNaN(value) && isNaN(last)))) {
dirty = true;
lastDirtyWatch = watch;
watch.last = watch.eq ? copy(value) : value;
watch.fn(value, ((last === initWatchVal) ? value : last), current);
if (ttl < 5) {
logIdx = 4 - ttl;
if (!watchLog[logIdx]) watchLog[logIdx] = [];
logMsg = (isFunction(watch.exp))
? 'fn: ' + (watch.exp.name || watch.exp.toString())
: watch.exp;
logMsg += '; newVal: ' + toJson(value) + '; oldVal: ' + toJson(last);
watchLog[logIdx].push(logMsg);
}
} else if (watch === lastDirtyWatch) {
// If the most recently dirty watcher is now clean, short circuit since the remaining watchers
// have already been tested.
dirty = false;
break traverseScopesLoop;
}
}
} catch (e) {
Expand All @@ -604,20 +619,24 @@ function $RootScopeProvider(){
// Insanity Warning: scope depth-first traversal
// yes, this code is a bit crazy, but it works and we have tests to prove it!
// this piece should be kept in sync with the traversal in $broadcast
if (!(next = (current.$$childHead || (current !== target && current.$$nextSibling)))) {
if (!(next = (current.$$childHead ||
(current !== target && current.$$nextSibling)))) {
while(current !== target && !(next = current.$$nextSibling)) {
current = current.$parent;
}
}
} while ((current = next));

// `break traverseScopesLoop;` takes us to here

if(dirty && !(ttl--)) {
clearPhase();
throw $rootScopeMinErr('infdig',
'{0} $digest() iterations reached. Aborting!\n' +
'Watchers fired in the last 5 iterations: {1}',
TTL, toJson(watchLog));
}

} while (dirty || asyncQueue.length);

clearPhase();
Expand Down
76 changes: 76 additions & 0 deletions test/ng/rootScopeSpec.js
View file
Original file line number Diff line number Diff line change
Expand Up @@ -577,6 +577,82 @@ describe('Scope', function() {
});
});
});


describe('optimizations', function() {

function setupWatches(scope, log) {
scope.$watch(function() { log('w1'); return scope.w1; }, log.fn('w1action'));
scope.$watch(function() { log('w2'); return scope.w2; }, log.fn('w2action'));
scope.$watch(function() { log('w3'); return scope.w3; }, log.fn('w3action'));
scope.$digest();
log.reset();
}


it('should check watches only once during an empty digest', inject(function(log, $rootScope) {
setupWatches($rootScope, log);
$rootScope.$digest();
expect(log).toEqual(['w1', 'w2', 'w3']);
}));


it('should quit digest early after we check the last watch that was previously dirty',
inject(function(log, $rootScope) {
setupWatches($rootScope, log);
$rootScope.w1 = 'x';
$rootScope.$digest();
expect(log).toEqual(['w1', 'w1action', 'w2', 'w3', 'w1']);
}));


it('should not quit digest early if a new watch was added from an existing watch action',
inject(function(log, $rootScope) {
setupWatches($rootScope, log);
$rootScope.$watch(log.fn('w4'), function() {
log('w4action');
$rootScope.$watch(log.fn('w5'), log.fn('w5action'));
});
$rootScope.$digest();
expect(log).toEqual(['w1', 'w2', 'w3', 'w4', 'w4action',
'w1', 'w2', 'w3', 'w4', 'w5', 'w5action',
'w1', 'w2', 'w3', 'w4', 'w5']);
}));


it('should not quit digest early if an evalAsync task was scheduled from a watch action',
inject(function(log, $rootScope) {
setupWatches($rootScope, log);
$rootScope.$watch(log.fn('w4'), function() {
log('w4action');
$rootScope.$evalAsync(function() {
log('evalAsync')
});
});
$rootScope.$digest();
expect(log).toEqual(['w1', 'w2', 'w3', 'w4', 'w4action', 'evalAsync',
'w1', 'w2', 'w3', 'w4']);
}));


it('should quit digest early but not too early when various watches fire', inject(function(log, $rootScope) {
setupWatches($rootScope, log);
$rootScope.$watch(function() { log('w4'); return $rootScope.w4; }, function(newVal) {
log('w4action');
$rootScope.w2 = newVal;
});

$rootScope.$digest();
log.reset();

$rootScope.w1 = 'x';
$rootScope.w4 = 'x';
$rootScope.$digest();
expect(log).toEqual(['w1', 'w1action', 'w2', 'w3', 'w4', 'w4action',
'w1', 'w2', 'w2action', 'w3', 'w4',
'w1', 'w2']);
}));
});
});


Expand Down

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