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Advanced cli progress bars

Gábor Csárdi

2024-11-13

Source: vignettes/progress-advanced.Rmd
progress-advanced.Rmd

Overhead

cli progress bars do have an overhead that may or may not be significant for your use case. In the R API, if you have a tight loop, then you should not update the progress bar too often.

Minimizing overhead

To minimize progress bar overhead, cli_progress_update() uses an internal timer and only update the progress bar on the screen if the timer is due.

In C code, you can refer to the timer directly to avoid an update. The CLI_SHOULD_TICK macro evaluates to one if the timer is due and an update is needed, otherwise to zero. CLI_SHOULD_TICK only works if you already created a cli progress bar from C, or you called cli_progress_init_timer(). The latter initializes the cli timer without creating a progress bar. (If the timer is not initialized, then CLI_SHOULD_TICK evaluates to zero.)

  SEXP bar = PROTECT(cli_progress_bar(num_iters, NULL));
  for (i = 0; i < num_iters; i++) {
    if (CLI_SHOULD_TICK) cli_progress_set(bar, i);
    // ...
  }
  cli_progress_done(bar);

Non-interactive R sessions

cli output is different if the terminal or platform is not dynamic, i.e. if it does not support the \r character to move the cursor to the beginning of the line without starting a new line. This often happens when R is running non-interactively and the standard error is redirected to a file. cli uses the cli::is_dynamic_tty() function to determine if the output supports \r.

On a non-dynamic terminal, cli simply prints progress updates as new lines to the screen. Frequently updating the progress in this fashion would produce a lot of output, so on non-dynamic terminals cli falls back to a slower timer update interval.

By default the cli timer signals every 3000 milliseconds in an R session without a dynamic terminal, instead of 200 milliseconds.

Progress bars in scripts

You can use progress bars in R scripts, just like you use them in R packages.

In an R script you might create a progress bar from the global environment, instead from within a function call. The global environment also has a current progress bar, so when you create a progress bar from the global environment, the previous one from the same environment is terminated. However, there is not function to return from, so the last progress bar of the script will be only terminated when the script terminates, or when you explicitly terminate it using cli_progress_done().

Customization

cli progress bars can be customized by the developer and the end user, by setting options, providing function arguments and regular cli themes.

Some aspects can only be customized by the developer, and some others can only be customized by the end user. Others can be customized by both, with the end user’s setting taking precedence.

Developer customization

About progress bar types

Each progress bar type has a default display (format string), which can be configured by the end user. The current progress bar types are, with their default display, with known and unknown number of total progress units.

iterator

Typically for loops and mapping functions. It shows a bar by default, if the total number of iterations is known.

tasks

For a list of tasks, by default it shows a current/total display.

download

For downloads, progress units are shown as bytes by default here.

custom

For custom displays, the developer has to specify an format string for custom progress bars.

Custom format strings (by the developer)

The developer can specify a custom format string for a progress bar. For custom progress bars, this is compulsory. Format strings may use glue templating, cli pluralization and cli theming. They can also use a number of built-in cli progress variables, see ‘Progress variables’ below.

f <- function() {
  cli_progress_bar(
    total = 20000,
    format = "Step {step} | {pb_bar} {pb_percent}"
  )
  step <- 1
  for (i in 1:10000) {
    Sys.sleep(2/10000)
    cli_progress_update(set = i)
  }
  step <- 2
  for (i in 10001:20000) {
    Sys.sleep(2/10000)
    cli_progress_update(set = i)
  }
}
f()

For custom progress bars cli always uses the specified format string. For other types, the end user might customize the format string, see below.

End user customization

Quick loops

The cli.progress_show_after (default is two seconds) option is the number seconds to wait before showing a progress bar.

Custom bars

The end user can customize how a progress bar will look, by setting one or more of the following options:

  • cli.progress_bar_style
  • cli.progress_bar_style_unicode
  • cli.progress_bar_style_ascii

On UTF-8 displays cli.progress_bar_style_unicode is used, if set. Otherwise cli.progress_bar_style is used. On non UTF-8 displays cli.progress_bar_style_ascii is used, if set. Otherwise cli.progress_bar_style is used.

These options can be set to a built-in progress bar style name:

names(cli_progress_styles())
#> [1] "classic"     "squares"     "dot"         "fillsquares" "bar"
options(cli.progress_bar_style = "fillsquares")
f <- function() lapply(cli_progress_along(letters), function(l) Sys.sleep(0.2))
x <- f()

Alternatively, they can be set to a list with entries complete, incomplete and current, to specify the characters (or strings) for the parts of the progress bar:

options(cli.progress_bar_style = list(
  complete = cli::col_yellow("\u2605"),
  incomplete = cli::col_grey("\u00b7")
))
f <- function() lapply(cli_progress_along(letters), function(l) Sys.sleep(0.2))
x <- f()

Custom spinners

Options to customize cli spinners:

  • cli.spinner
  • cli.spinner_unicode
  • cli.spinner_ascii

On UTF-8 displays cli.spinner_unicode is used, if set, otherwise cli.spinner. On ASCII displays cli.spinner_ascii is used, if set, otherwise cli.spinner.

Use list_spinners() to list all spinners and demo_spinners() to take a peek at them.

options(cli.spinner = "moon")
f <- function() {
  cli_progress_bar(format = strrep("{cli::pb_spin} ", 20), clear = TRUE)
  for (i in 1:100) {
    Sys.sleep(5/100)
    cli_progress_update()
  }
}
f()

Custom format strings

The end user may use a number of global options to customize how the built-in progress bar types are displayed on the screen:

  • cli.progress_format_iterator is used for iterator progress bars.
  • cli.progress_format_iterator_nototal is used for iterator progress bars with an unknown number of total units.
  • cli.progress_format_tasks is used for tasks progress bars.
  • cli.progress_format_tasks_nototal is used for tasks progress bars with an unknown number of total units.
  • cli.progress_format_download is used for download progress bars.
  • cli.progress_format_download_nototal is used for download progress bars with an unknown number of total units.

Progress variables

Custom format strings may use progress variables in glue interpolated expressions, to refer to the state of the progress bar. See ?"progress-variables" in the manual for the list of supported variables.

If you refer to a progress variable from a package, you need need to import it or qualify the reference with cli::. When you set a custom format string as an end user option, we suggest that you always use the qualified form, in case the cli package is not attached. For example, to set a minimal display for downloads you might write

options(cli.progress_format_download =
  paste0(
    "{cli::col_cyan('\u2B07')} {cli::pb_spin} ",
    "{cli::pb_name}[{cli::pb_current_bytes}/{cli::pb_total_bytes}]"
  )
)

to get

You can use your own expressions and functions on progress bar tokens. E.g. to show the current number of steps with letters instead of numbers, use letters[pb_current]:

f <- function() {
  cli_progress_bar(
    total = 26,
    format = "{pb_spin} This is step {.emph {letters[pb_current]}}. {pb_spin}"
  )
  for (i in 1:26) {
    Sys.sleep(3/26)
    cli_progress_update()
  }
}
f()

Clearing or keeping terminated progress bars

By default terminated progress bars are removed from the screen. The end user can set the cli.progress_clear option to FALSE to override the default. In addition, the developer can also change the default, using the clear parameter of cli_progress_bar(). If both the option and the parameter are set, the parameter is used.

The C API

To use the C cli progress API in your package, you need to add cli to LinkingTo and Imports:

LinkingTo: cli
Imports: cli

In the C files you want to use the API from include cli/progress.h:

#include <cli/progress.h>

Now you are ready to call cli functions. The C API is similar to the traditional R API:

  1. cli_progress_bar() creates a progress bar.
  2. cli_progress_update() updates a progress bar.
  3. cli_progress_done() terminates it.

A complete example:

SEXP progress_test1() {
  int i;
  SEXP bar = PROTECT(cli_progress_bar(1000, NULL));
  for (i = 0; i < 1000; i++) {
    cli_progress_sleep(0, 4 * 1000 * 1000);
    if (CLI_SHOULD_TICK) cli_progress_set(bar, i);
  }
  cli_progress_done(bar);
  UNPROTECT(1);
  return Rf_ScalarInteger(i);
}

C API reference

CLI_SHOULD_TICK

A macro that evaluates to (int) 1 if a cli progress bar update is due, and to (int) 0 otherwise. If the timer hasn’t been initialized in this compilation unit yet, then it is always 0. To initialize the timer, call cli_progress_init_timer() or create a progress bar with cli_progress_bar().

cli_progress_add() 

void cli_progress_add(SEXP bar, double inc);

Add a number of progress units to the progress bar. It will also trigger an update if an update is due.

  • bar: progress bar object.
  • inc: progress increment.

cli_progress_bar() 

SEXP cli_progress_bar(double total, SEXP config);

Create a new progress bar object. The returned progress bar object must be PROTECT()-ed.

  • total: Total number of progress units. Use NA_REAL if it is not known.
  • config: R named list object of additional parameters. May be NULL (the C NULL~) orR_NilValue(the RNULL`) for the defaults.

config may contain the following entries:

  • name: progress bar name.
  • status: (initial) progress bar status.
  • type: progress bar type.
  • total: total number of progress units.
  • show_after: show the progress bar after the specified number of seconds. This overrides the global show_after option.
  • format: format string, must be specified for custom progress bars.
  • format_done: format string for successful termination.
  • format_failed: format string for unsuccessful termination.
  • clear: whether to remove the progress bar from the screen after termination.
  • auto_terminate: whether to terminate the progress bar when the number of current units equals the number of total progress units.
Example 
#include <cli/progress.h>
SEXP progress_test1() {
  int i;
  SEXP bar = PROTECT(cli_progress_bar(1000, NULL));
  for (i = 0; i < 1000; i++) {
    cli_progress_sleep(0, 4 * 1000 * 1000);
    if (CLI_SHOULD_TICK) cli_progress_set(bar, i);
  }
  cli_progress_done(bar);
  UNPROTECT(1);
  return Rf_ScalarInteger(i);
}

cli_progress_done() 

void cli_progress_done(SEXP bar);

Terminate the progress bar.

  • bar: progress bar object.

cli_progress_init_timer() 

void cli_progress_init_timer();

Initialize the cli timer without creating a progress bar.

cli_progress_num() 

int cli_progress_num();

Returns the number of currently active progress bars.

cli_progress_set() 

void cli_progress_set(SEXP bar, double set);

Set the progress bar to the specified number of progress units.

  • bar: progress bar object.
  • set: number of current progress progress units.

cli_progress_set_clear() 

void cli_progress_set_clear(SEXP bar, int clear);

Set whether to remove the progress bar from the screen. You can call this any time before cli_progress_done() is called.

  • bar: progress bar object.
  • clear: whether to remove the progress bar from the screen, zero or one.

cli_progress_set_format() 

void cli_progress_set_format(SEXP bar, const char *format, ...);

Set a custom format string for the progress bar. This call does not try to update the progress bar. If you want to request an update, call cli_progress_add(), cli_progress_set() or cli_progress_update().

  • bar: progress bar object.
  • format: format string.
  • ...: values to substitute into format.

format and ... are passed to vsnprintf() to create a format string.

Format strings may contain glue substitutions, referring to progress variables, pluralization, and cli styling.

cli_progress_set_name() 

void cli_progress_set_name(SEXP bar, const char *name);

Set the name of the progress bar.

  • bar; progress bar object.
  • name: progress bar name.

cli_progress_set_status() 

void cli_progress_set_status(SEXP bar, const char *status);

Set the status of the progress bar.

  • bar: progress bar object.
  • status: progress bar status.

cli_progress_set_type() 

void cli_progress_set_type(SEXP bar, const char *type);

Set the progress bar type. Call this function right after creating the progress bar with cli_progress_bar(). Otherwise the behavior is undefined.

  • bar: progress bar object.
  • type: progress bar type. Possible progress bar types: iterator, tasks, download and custom.

cli_progress_update() 

void cli_progress_update(SEXP bar, double set, double inc, int force);

Update the progress bar. Unlike the simpler cli_progress_add() and cli_progress_set() function, it can force an update if force is set to 1.

  • bar: progress bar object.
  • set: the number of current progress units. It is ignored if negative.
  • inc: increment to add to the current number of progress units. It is ignored if set is not negative.
  • force: whether to force an update, even if no update is due.

To force an update without changing the current number of progress units, supply set = -1, inc = 0 and force = 1.