Still very much a draft but I've settled on two approaches:
Calculating the fibonacci sequence either approach performs about 5x better
than the curent scheduler.
Fibonacci sequence is thousands of very short operations so it does very
well the more the duration check is skipped. Real world tasks won't
improve nearly as much but I think most code should get a 10 to 15% speed
increase.
First approach skips loops based on how many times it ran last time (This
is faster than second but I think more dangerous and only works if you're
running a single task):
private int lastLoopCount;
/**
* Execute a list of Tasks that hold RepeatingCommands.
*
* @return A replacement array that is possibly a shorter copy of
<code>tasks</code>
*/
private JsArray<Task> runRepeatingTasks(JsArray<Task> tasks) {
assert tasks != null : "tasks";
int length = tasks.length();
if (length == 0) {
return null;
}
boolean canceledSomeTasks = false;
Duration duration = createDuration();
int loopCount = lastLoopCount;
boolean skipLoop = false;
if (length == 1 && lastLoopCount > 0) {
while (lastLoopCount-- > 0 ) {
if (!tasks.get(0).executeRepeating()) {
tasks.set(0, null);
canceledSomeTasks = true;
}
}
skipLoop = canceledSomeTasks || duration.elapsedMillis() >=
TIME_SLICE;
}
if (skipLoop) {
lastLoopCount -= 2;
} else {
while (duration.elapsedMillis() < TIME_SLICE) {
boolean executedSomeTask = false;
for (int i = 0; i < length; i++) {
assert tasks.length() == length : "Working array length changed "
+ tasks.length() + " != "
+ length;
Task t = tasks.get(i);
if (t == null) {
continue;
}
executedSomeTask = true;
assert t.isRepeating() : "Found a non-repeating Task";
if (!t.executeRepeating()) {
tasks.set(i, null);
canceledSomeTasks = true;
}
loopCount += 1;
}
if (!executedSomeTask) {
//no work left to do, break to avoid busy waiting until
TIME_SLICE is reached
break;
}
}
if (length == 1) {
lastLoopCount = loopCount;
}
}
if (canceledSomeTasks) {
lastLoopCount = 0;
JsArray<Task> newTasks = createQueue();
// Remove tombstones
for (int i = 0; i < length; i++) {
if (tasks.get(i) != null) {
newTasks.push(tasks.get(i));
}
}
assert newTasks.length() < length;
return newTasks.length() == 0 ? null : newTasks;
} else {
return tasks;
}
}
Second approach checks how much time is elapsed and how many times the task
has been run and then calculates how many times the task can be run before
it needs to check the elapsed time again. (This is very slightly slower
than the above but can be made to work with multiple tasks and I think will
be easier to make safe, although isn't safe at the moment):
/**
* Execute a list of Tasks that hold RepeatingCommands.
*
* @return A replacement array that is possibly a shorter copy of
* <code>tasks</code>
*/
private JsArray<Task> runRepeatingTasks(JsArray<Task> tasks) {
assert tasks != null : "tasks";
int length = tasks.length();
if (length == 0) {
return null;
}
boolean canceledSomeTasks = false;
Duration duration = createDuration();
int runCount = 0;
int quickRunCount = 0;
int elapsedMillis = duration.elapsedMillis();
while ( elapsedMillis < TIME_SLICE) {
boolean executedSomeTask = false;
for (int i = 0; i < length; i++) {
assert tasks.length() == length : "Working array length
changed " + tasks.length() + " != " + length;
Task t = tasks.get(i);
if (t == null) {
continue;
}
executedSomeTask = true;
assert t.isRepeating() : "Found a non-repeating Task";
if (!t.executeRepeating()) {
tasks.set(i, null);
canceledSomeTasks = true;
}
}
if (!executedSomeTask) {
// no work left to do, break to avoid busy waiting until
// TIME_SLICE is reached
break;
}
runCount += 1;
if (quickRunCount-- <= 0) {
elapsedMillis = duration.elapsedMillis();
if (elapsedMillis > 0) {
quickRunCount = (int) (((TIME_SLICE - 1) * runCount) /
elapsedMillis);
}
}
}
if (canceledSomeTasks) {
JsArray<Task> newTasks = createQueue();
// Remove tombstones
for (int i = 0; i < length; i++) {
if (tasks.get(i) != null) {
newTasks.push(tasks.get(i));
}
}
assert newTasks.length() < length;
return newTasks.length() == 0 ? null : newTasks;
} else {
return tasks;
}
}
On Wed, Jan 14, 2015 at 4:07 PM, Richard Wallis <[email protected]> wrote:
> Just an update, there's a bug in my original implementation which causes
> the loopCounter to tend to increase until the task ends.
>
> After removing the bug, the performance increase is only about 8% for the
> fibonacci sequence.
>
> Also the safer version where the loopCounter increments by at most 1
> eliminates the performance gain for the fibonacci test because the task
> runs 8000 to 9000 times during each loop so the loopCounter never gets
> anywhere close to a number that will make a difference.
>
>
> On Wed, Jan 14, 2015 at 2:19 PM, Richard Wallis <[email protected]>
> wrote:
>
>> Actually in defense of adding the optimization to the current api.
>>
>> It can be made safe by only ever setting lastLoopCounter to
>> min(lastLoopCounter + 1, loopCounter).
>>
>> That should cause similar improved performance for multiple second tasks
>> without ever having a lower frame rate than the current scheduler.
>>
>> On Wed, Jan 14, 2015 at 1:41 PM, Richard Wallis <[email protected]>
>> wrote:
>>
>>> You can't use webworkers to process the dom / xml, or do layout which is
>>> pretty much all my long running tasks do.
>>>
>>> Agree this is too dangerous to just add to the existing api but if you
>>> added a new method scheduleConstantTime() that ran the optimization it
>>> might be useful.
>>>
>>>
>>> On Wed, Jan 14, 2015 at 1:27 PM, 'Daniel Kurka' via GWT Contributors <
>>> [email protected]> wrote:
>>>
>>>> I think we do not want to make any assumptions about runtime of any
>>>> tasks since this would not work well with task that have variable runtime.
>>>>
>>>> If you need to do heavy calculations since browser APIs have evolved a
>>>> lot you should be using web workers anyway.
>>>>
>>>> On Wed, Jan 14, 2015 at 11:57 AM, Richard Wallis <[email protected]>
>>>> wrote:
>>>>
>>>>> At the moment, incremental scheduler runs a repeating task in a while
>>>>> loop that checks if its duration has exceeded 16ms and then returns
>>>>> control
>>>>> to the browser.
>>>>>
>>>>> If you assume that an incrementally scheduled task will tend to run in
>>>>> about the same time as it did before then you can get about a 10% speed up
>>>>> by counting the number of times the task ran during the last duration loop
>>>>> and then running the task that many times at the start (and skipping the
>>>>> duration check).
>>>>>
>>>>> On chrome a task that calculated the fibonacci sequence managed to
>>>>> calculate about 450000 numbers in a second with the current scheduler and
>>>>> about 500000 numbers in the same time with my new one below.
>>>>>
>>>>> And a realworld task that parses xml dropped from taking about 50
>>>>> seconds each run to 42 seconds.
>>>>>
>>>>> Of course if the incrementally scheduled task tends to take a longer
>>>>> and longer time to complete on each run the oprimization might cause
>>>>> issues
>>>>> so maybe we need to create a new kind of task scheduler specifically for
>>>>> tasks that tend to complete their runs in a similar timeframe.
>>>>>
>>>>> I'm looking for critiscim of the code below, (and maybe someone to
>>>>> take ownership of this and do a PR to gerrit on my behalf)
>>>>>
>>>>> In SchedulerImpl replace the current runRepeatingTasks method with
>>>>> this: (lastLoopCount is a private int field);
>>>>>
>>>>> /**
>>>>> * Execute a list of Tasks that hold RepeatingCommands.
>>>>> *
>>>>> * @return A replacement array that is possibly a shorter copy of
>>>>> <code>tasks</code>
>>>>> */
>>>>> private JsArray<Task> runRepeatingTasks(JsArray<Task> tasks) {
>>>>> assert tasks != null : "tasks";
>>>>>
>>>>> int length = tasks.length();
>>>>> if (length == 0) {
>>>>> return null;
>>>>> }
>>>>>
>>>>> boolean canceledSomeTasks = false;
>>>>>
>>>>> Duration duration = createDuration();
>>>>> int loopCount = 0;
>>>>> outer: while (duration.elapsedMillis() < TIME_SLICE) {
>>>>>
>>>>> if (length == 1) {
>>>>> while (lastLoopCount-- > 0 ) {
>>>>> if (!tasks.get(0).executeRepeating()) {
>>>>> tasks.set(0, null);
>>>>> canceledSomeTasks = true;
>>>>> break outer;
>>>>> }
>>>>> loopCount += 1;
>>>>> }
>>>>> }
>>>>> boolean executedSomeTask = false;
>>>>> for (int i = 0; i < length; i++) {
>>>>> assert tasks.length() == length : "Working array length
>>>>> changed " + tasks.length() + " != "
>>>>> + length;
>>>>> Task t = tasks.get(i);
>>>>> if (t == null) {
>>>>> continue;
>>>>> }
>>>>> executedSomeTask = true;
>>>>>
>>>>> assert t.isRepeating() : "Found a non-repeating Task";
>>>>>
>>>>> if (!t.executeRepeating()) {
>>>>> tasks.set(i, null);
>>>>> canceledSomeTasks = true;
>>>>> }
>>>>> loopCount += 1;
>>>>> }
>>>>> if (!executedSomeTask) {
>>>>> // no work left to do, break to avoid busy waiting until
>>>>> TIME_SLICE is reached
>>>>> break;
>>>>> }
>>>>> }
>>>>> if (length == 1) {
>>>>> lastLoopCount = loopCount;
>>>>> }
>>>>>
>>>>> if (canceledSomeTasks) {
>>>>> lastLoopCount = 0;
>>>>> JsArray<Task> newTasks = createQueue();
>>>>> // Remove tombstones
>>>>> for (int i = 0; i < length; i++) {
>>>>> if (tasks.get(i) != null) {
>>>>> newTasks.push(tasks.get(i));
>>>>> }
>>>>> }
>>>>> assert newTasks.length() < length;
>>>>> return newTasks.length() == 0 ? null : newTasks;
>>>>> } else {
>>>>> return tasks;
>>>>> }
>>>>> }
>>>>>
>>>>> --
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>>>>> <https://groups.google.com/d/msgid/google-web-toolkit-contributors/80297aa7-c49a-4e3b-b70a-554bfaef52f0%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>> .
>>>>> For more options, visit https://groups.google.com/d/optout.
>>>>>
>>>>
>>>>
>>>>
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