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Ask Slashdot: Why Is It So Hard To Make An Accurate Progress Bar?
hyperorbiter writes "How come after 25 years in the tech industry, someone hasn't worked out how to make accurate progress bars? This migration I'm doing has sat on 'less than a minute' for over 30 minutes. I'm not an engineer; is it really that hard?"
Yes it is "that hard".
I did it all for the penguins!
Things are asyncronous. You wait for things from disk, ram, user input, over the network etc. How long it will take is non-deterministic. So a task composed of a bunch of these little pieces will be non-deterministic too.
One reason is the progress bar starts out as just a generic tool to show that your loading hasn't froze. At first it is parsed correctly with the elements to be loaded, but as scope increases and more things load, it can get sketchy later on.
Another reason is it is difficult to estimate time left. If you look at some old FTP programs, they'd estimate the rest of the download's time based on how fast the previous has taken. Future lag, fragmented files, etc aren't taken into consideration.
There's a bunch more reasons, but namely the progress bar's main purpose is to show you that the whole system isn't locked up, which they've been doing well for the past 30 years or so.
God spoke to me
It's very hard to predict how long something will take, particularly in relation to other things, if what you're writing is going to be on any number of platforms with different processors, storage, memory and network situations.
You can be reasonably accurate with it, far more than my favorite 99% in 1 second, the last 1% in one hour scenario. There are cleverer and cleverer ways of making it ever more precise, but those methods usually involve spending time on getting it right, and not many people do it.
Consider this: Once you've put progress on a bar, you can't take it off. Suppose you start a process that should take 20 minutes, and do the first 5 minutes, progress is now at 25%. But then, partway through, something unexpected happens and you realize the process is actually going to take 40 minutes. You can't take the progress "back" now, that would disorient the user. So you have to rescale the remainder of the bar.
For over 50 years rocket launch countdowns have not run in a linear fashion, sometimes even being set backwards.
... when we solve the halting problem. I'm not entirely joking. The main problem with progress bars is that, quite often, it is not possible to accurately estimate how much time is needed to complete a problem (i.e. for the program to halt).
Loban Amaan Rahman ==> Anagram of ==> Aha! An Abnormal Man!
The public opinion of the Progress Bar would be considerably more favorable if programmers would simply treat 100% as if it were 75%.
In other words, do all the stuff you have to do, measuring progress and whatnot, but when you're actually at 80%, report yourself at 60%. Likewise, when you're at 95%, say you're at 70%.
Then, only when you really are completely finished, you jump from 75% to 100% in under a second.
Complaints gone.
-David
You know what I'd like to see more than a working progress bar? A "Cancel" button that actually stops the f*%! process! .
I don't want to finish the sub-process I'm currently doing (which has probably stalled)... just FREAKING STOP.
If you (programmer) want to close connections, or save the changes to the disk, do it in the background. Making me sit there for another 10 minutes while you're "cancelling..." is not helpful. I will force close your program. Failing that I will hard-reset the computer. Seriously.
Unlike porn, which yada yada rimshot hey-ooh!
Give this man some upward moderation.
The problem is that the question is wrong. It's trivial to make a progress bar...just sum up all the things you have to do, and move the bar each time a "thing" is done, rounding to the nearest pixel. It doesn't matter if the "thing" is a byte to copy, a file to install, or any generic task. As long as you can add one to a counter each time you have done another "thing", you can then display it graphically.
The actual complaint is about displaying accurate time remaining to complete the task, which really has nothing to do with the display of the progress bar. Instead, it involves guessing about how long each remaining "thing" will take to complete, and then displaying that sum of those times. This is hard because no matter how accurate the data used to make the guess, something outside the control of the program can disrupt the processing.
"How come after 25 years in the tech industry, someone hasn't worked out how to make accurate progress bars? This migration I'm doing has sat on 'less than a minute' for over 30 minutes. I'm not an engineer; is it really that hard?"
Yes, because all progress bars are inherently a prediction of things that will happen in the future. If there is any error condition, unusually large blob of data or weirdly structured hard drive to read from, varying bandwidth bottleneck, fritzy peripheral not responding as expected, etc., etc. times a million, then the unusual event will make the prior prediction incorrect and look silly in retrospect. As long as there is any "if-then" clause or error handling in the branches in the system, then the unexpected can happen and make the prediction (progress bar) invalid.
It's analogous to weather prediction. It can't be perfect, it's an extrapolation, but people will always complain about it.
We know where leadership by an anti-intellectual "strongman" who scapegoats minorities and likes boisterous rallies goes
Show progress of the work, not the time. You never know what other things the machine is doing, and is better to give no estimate than a bad one.
And don't suffice with a bar, also provide information on what the process is doing.
-- The Internet is a too slow way of doing things, you'd never do without it.
Except even the number of tasks is often variable over the life of the task.
Take for example loading a web page. It starts out as 1 task: Get a page from the server. Once you've done that, how many more requests will that first request generate? Impossible to tell. It could be none. It could be hundreds, and some of those can generate their own requests. (etc, etc.)
The answer is this: Some feedback, no matter how incorrect, is better than no feedback at all.
Progress should be reported to the user in outline format. Give the user the list of tasks that the computer is working on, show progress in each task. This is much more informative, and as a user - i'd feel more intimate with the process and in turn more trusting. also this might allow me to troubleshoot things that are moving slowly. some games are great at this, i've never seen it in an OS though.