RcppProgress is a tool to help you monitor the execution time of your C++ code, by providing a way to interrupt the execution inside the C++ code, and also to display a progress bar indicative of the state of your computation. Additionally, it is compatible with multi-threaded code, for example using OpenMP. The initial (yet updated) article explains the basic setup.
Since version 0.4 it became more simple to create custom progress bars. In this new article we will show how to do this. Our final example displays a progress bar which provides an estimation of the remaining time (ETA) to finish a computation.
A minimal example
Imagine you added a progress bar with RcppProgress to your function
long_computation() following the example from the first article mentioned above.
What you get is a basic and useful console visualization that looks like this:
0% 10 20 30 40 50 60 70 80 90 100% [----|----|----|----|----|----|----|----|----|----| ******************************
That’s the default, platform independent display in RcppProgress defined in SimpleProgressBar.hpp. It’s OK for most purposes to give you an idea how much work is done and it also allows you to make a very intuitive estimation about how long it’s going to take to finish. But of course that’s not everything a progress bar could show you. A progress bar could give you information about the running progress or about performance parameters of your system. It could contain calculated estimates of passed and remaining time. After all it could just look much more fancy to impress your colleagues.
RcppProgress makes it now easy to create your own implementation of a progress bar class.
Your own class has to be derived from the abstract class
ProgressBar that defines some
basic virtual methods:
display() starts the display that will be updated by subsequent calls of
end_display finalizes it. Your progress bar implementation should
not rely on the destructor to finalize the display.
A very minimal setup could look something like this:
display() method in this example does nothing more than printing the word
update() concatenates a
+ symbol every time
called. The result looks like this:
In comparison to the example of the default progress bar above, I moved the
increment() out of the second level and into the first level loop to keep
the amount of console output at bay.
update() also checks if the display is
end_display triggers the finalization.
Remaining time estimation
Based on the minimal setup above, you can implement more sophisticated
progress bars. Here’s an example of one that looks exactly like the default
SimpleProgressBar, but adds an estimation of the remaining time for the process to finish.
You can find a complete package setup with the code for this ETAProgressBar
In this article we only highlight some crucial aspects of the implementation.
We use the Rinterface.h header to update the display dynamically. Unfortunately this header is only available for Unix-like systems. A less cool, old version of an ETA progress bar that also works on windows can be found here. The following preprocessor statements load Rinterface.h if the code is compiled on a non-windows computer.
ETAProgressBar inherits from the abstract class
It has an integer variable
_max_ticks that controls the amount of individual
tick symbols necessary to reach the 100% mark of the progress bar. That depends
on the display you want to craft.
ETAProgressBar also has a boolean flag variable
_timer_flag that acts as a switch to separate the initial starting turn where
the time measurement starts and the following turns where the time is picked off.
The measured time values are stored in two variables
end of class
time_t (from ctime).
display() function initializes the progress bar visualization. The first two lines
are hard coded ASCII art.
update() is the most important function for the progress bar mechanism. The if clause
allows to separate the initial call of
update() from the following ones to start the time
counter. Afterwards the time passed is calculated and transformed to a human readable string
by the custom function
_current_ticks_display() is another custom
function to transform the progress information to a string with the correct amount of
symbols and filling whitespaces. The progress string and the time string are concatenated
to create the additional third line below the initial two lines drawn by
A string with sufficient whitespaces is also added to ensure that this dynamically updated
line is overwritten completely from turn to turn.
REprintf("\r"); triggers a carriage return
to make this continuous overwriting possible.
_time_to_string() parses time information given in form of a floating point number of
seconds to a human-readable string. The basic algorithm is based on an example from
_current_ticks_display() relies on
_compute_nb_ticks() to first of all transform
the progress information (floating point number between 0 and 1) to a natural number
that expresses the correct fraction of
takes this value and parses a string with
* symbols and whitespaces that can be plotted
as a visual progress indication.
flush_console() is a wrapper around
R_FlushConsole() which is called to flush any
pending output to the system console. It’s necessary to do this when the display is started
display() and when it’s closed in
The output of an
ETAProgressBar looks like this:
0% 10 20 30 40 50 60 70 80 90 100% [----|----|----|----|----|----|----|----|----|----| |******* | 49s