<!--
%\VignetteIndexEntry{progressr: Appendix}
%\VignetteAuthor{Henrik Bengtsson}
%\VignetteKeyword{R}
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%\VignetteKeyword{vignette}
%\VignetteKeyword{packages}
%\VignetteEngine{progressr::selfonly}
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## How tos

### Report on progress in non-interactive mode ("batch mode")

When running R from the command line, R runs in a non-interactive mode
(`interactive()` returns `FALSE`).  The default behavior of
**progressr** is to _not_ report on progress in non-interactive mode.
To report on progress also then, set R options `progressr.enable` or
environment variable `R_PROGRESSR_ENABLE` to `TRUE`.  For example,

```sh
$ Rscript -e "library(progressr)" -e "with_progress(y <- slow_sum(1:10))"
```

will _not_ report on progress, whereas

```sh
$ export R_PROGRESSR_ENABLE=TRUE
$ Rscript -e "library(progressr)" -e "with_progress(y <- slow_sum(1:10))"
```

will.


## Notes of caution

### Avoid sending progress updates too frequently

Signaling progress updates comes with some overhead.  In situations
where we use progress updates, this overhead is typically much smaller
than the task we are processing in each step.  However, if the task we
iterate over is quick, then the extra time induced by the progress
updates might end up dominating the overall processing time.  If that
is the case, a simple solution is to only signal progress updates
every nth step.  Here is a version of `slow_sum()` that signals
progress every 10th iteration:

```
slow_sum <- function(x) {
  p <- progressr::progressor(length(x) / 10)
  sum <- 0
  for (kk in seq_along(x)) {
    Sys.sleep(0.1)
    sum <- sum + x[kk]
    if (kk %% 10 == 0) p(message = sprintf("Adding %g", x[kk]))
  }
  sum
}
```

The overhead of progress signaling may depend on context.  For
example, in parallel processing with near-live progress updates via
'multisession' futures, each progress update is communicated via a
socket connections back to the main R session.  These connections
might become clogged up if progress updates are too frequent.


## Known Limitations

### The global progress handler cannot be set during package load

It is _not_ possible to call `handlers(global = TRUE)` in all
circumstances.  For example, it cannot be called within `tryCatch()`
and `withCallingHandlers()`;

```r
> tryCatch(handlers(global = TRUE), error = identity)
Error in globalCallingHandlers(NULL) :
  should not be called with handlers on the stack
```

This is not a bug - neither in **progressr** nor in R itself. It's due
to a conservative design on how _global_ calling handlers should work
in R. If it were allowed, there's a risk we might end up getting weird and
unpredictable behaviors when messages, warnings, errors, and other
types of conditions are signaled.

Because `tryCatch()` and `withCallingHandlers()` are used in many
places throughout base R, this means that we also cannot call
`handlers(global = TRUE)` as part of a package's startup process,
e.g. `.onLoad()` or `.onAttach()`.

Another example of this error is if `handlers(global = TRUE)` is used
inside package vignettes and dynamic documents such as Rmarkdown.  In
such cases, the global progress handler has to be enabled _prior_ to
processing the document, e.g.

```r
> progressr::handlers(global = TRUE)
> rmarkdown::render("input.Rmd")
```


### A progressor cannot be created in the global environment

It is not possible to create a progressor in the global environment,
e.g. in the top-level of a script. It can only be created inside a
function, within `with_progress({ ... })`, `local({ ... })`, or a
similar construct.  For example, the following:

```r
library(progressr)
handlers(global = TRUE)

xs <- 1:5
p <- progressor(along = xs)
y <- lapply(xs, function(x) {
  Sys.sleep(0.1)
  p(sprintf("x=%g", x))
  sqrt(x)
})
```

results in an error if tried:

```
Error in progressor(along = xs) :
  A progressor must not be created in the global environment unless wrapped in a
  with_progress() or without_progress() call. Alternatively, create it inside a
  function or in a local() environment to make sure there is a finite lifespan
  of the progressor
```

The solution is to wrap it in a `local({ ... })` call, or more
explicitly, in a `with_progress({ ... })` call:

```r
library(progressr)
handlers(global = TRUE)

xs <- 1:5
with_progress({
  p <- progressor(along = xs)
  y <- lapply(xs, function(x) {
    Sys.sleep(0.1)
    p(sprintf("x=%g", x))
    sqrt(x)
  })
})
#  |====================                               |  40%
```

The main reason for this is to limit the lifespan of each progressor.
If we created it in the global environment, there is a significant
risk it would never finish and block all of the following progressors.


### No coloring by the 'cli' and 'crayon' packages

The **[cli]** package can be used to output colored text and messages
in the terminal, e.g. `message(cli::col_blue("hey"))`. However,
**cli** disables such coloring by default when there is an active
progressor. The workaround is to set **cli** option `cli.num_colors` to:

```r
options(cli.num_colors = cli::num_ansi_colors())
```

This will force **cli** to use the same number of colors with and
without an active progressor.

The same happens when using the superseeded **[crayon]** package for
colorization. To re-enable coloring for **crayon**, set the same
(sic!)  above R options.

The technical reason for **cli** and **crayon** disabling coloring, is
that the **progressr** package buffers standard output using a sink,
which these packages consider to be mono-color only.


## Known Issues

### RStudio bug #16331: Setting global progressr handlers during startup does not work

Setting the global progressr handler in `~/.Rprofile` does _not_ work
in RStudio 2025.09:

```r
if (requireNamespace("progressr", quietly = TRUE)) {
  progressr::handlers(global = TRUE)
}
```

This is due to a [bug introduced in RStudio
2025.09](https://github.com/rstudio/rstudio/issues/16331), which has
been fixed for the next release RStudio 2025.11. If you are using
RStudio 2025.09, the workaround is to instead use:

```r
if (requireNamespace("progressr", quietly = TRUE)) {
  progressr::handlers(global = TRUE)

  ## Workaround for RStudio 2025.09 console bug #16331
  if (nzchar(Sys.getenv("RSTUDIO")) && !nzchar(Sys.getenv("RSTUDIO_TERM"))) {
    invisible(addTaskCallback(function(...) {
      ver <- RStudio.Version()$version
      if (ver >= "2025.09" && ver < "2025.11") {
        message("Workaround for RStudio 2025.09 bug #16331: Added progressr global handler")
        progressr::handlers(global = TRUE)
      } else {
        warning("Workaround for RStudio 2025.09 bug #16331: Not needed in RStudio v", ver, ". Please remove task callback 'rstudio::progressr::once' in your Rprofile startup file", call. = FALSE, immediate. = TRUE)
      }
      removeTaskCallback("rstudio::progressr::once")
    }, name = "rstudio::progressr::once"))
  }
}
```


### Positron bug #6892: Setting global progressr handlers during startup does not work

Positron does not support setting global calling handlers during R's
startup process, e.g. in `~/.Rprofile`. Even if such handlers are
registered, they have no effect. This is a [bug in
Positron](https://github.com/posit-dev/positron/issues/6892)
(2025-03-20), which was most recently confirmed with Position
2025.09.0 on Linux. Because of this, having something like in your
`~/.Rprofile`:

```r
if (requireNamespace("progressr", quietly = TRUE)) {
  progressr::handlers(global = TRUE)
}
```

will have no effect. If used, the workaround is to manually
re-registering all calling handlers, which can be done as:

```r
if (requireNamespace("progressr", quietly = TRUE)) {
  progressr::handlers(global = TRUE)

  ## Workaround for Positron (>= 2025.09) bug #16331
  if (nzchar(Sys.getenv("POSITRON"))) local({
    ver <- numeric_version(Sys.getenv("POSITRON_VERSION"))
    if (ver >= "2025.09") {
      message("Workaround for Positron (>= 2025.09) bug #6892: progressr global handler will be installed *after* the next call has been completed")
      invisible(addTaskCallback(function(...) {
        message("Workaround for Positron (>= 2025.09) bug #6892: re-installed progressr global handler")
        globalCallingHandlers(globalCallingHandlers(NULL))
        removeTaskCallback("positron::progressr::once")
      }, name = "positron::progressr::once"))
    }
  })
}
```

Alternatively, call:

```r
globalCallingHandlers(globalCallingHandlers(NULL))
```

or

```r
progressr::handlers(global = FALSE)  ## important
progressr::handlers(global = TRUE)
```

at the prompt.


### Positron: Messages add extra newline before the final progress step

One of the features of **progressr** is that messages are buffered
during progress reporting and relayed as soon as possible, which
typically happens just before handlers re-render the progress
output. This way you can use `message()` as usual, regardless whether
progress is reported or not.

Currently, when using Positron (e.g. Positron 2025.09.0), any
`message()` output adds an extra newline before the _final_ progress
step is reported, e.g.

```r
> progressr::handlers(global = TRUE)
> progressr::handlers("cli")
> y <- progressr::slow_sum(1:5, message = TRUE)
M: Added value 1
M: Added value 2
M: Added value 3
M: Added value 4

M: Added value 5
> 
```

I do not fully understand the reason for this, but I hope we can get
to the bottom of it and fix it, either in **progressr** or in
Positron, e.g. [Bug #9486](https://github.com/posit-dev/positron/issues/9486)
(2025-09-18).


### Jupyter: Reporting progress to stderr (default) does not work

The default for most terminal progress renders, including the ones for
**progressr**, display the progress on standard error (stderr). Due to
a limitation in Jupyter, this default does not work there. The reason is
that [Jupyter silently
drops](https://github.com/futureverse/progressr/issues/170) any output
sent to stderr, e.g.

```r
> cat("hello stderr\n", file = stderr())
> cat("hello stdout\n", file = stdout())
hello stdout
>
```

If we try the following

```r
library(progressr)
handlers(globals = TRUE)
handlers("txtprogressbar")
y <- slow_sum(1:20)
```

there will be no progress being reported. This is not specific to
**progressr**, we have the same problem with for instance **cli**. Try
for instance,

```r
void <- cli::cli_progress_demo(delay = 1.0)
```

The workaround is to direct all progress output to the standard output
(stdout) when working in Jupyter. For this to work, we also need to
disable the buffering ("delaying") of any other output to stdout.

```r
library(progressr)
handlers(globals = TRUE)

## Workaround for Jupyter
options(progressr.enable = TRUE, progressr.delay_stdout = FALSE)

## Jupyter requires that progress is rendered to standard output;
## it does not work with the default standard error
handlers(handler_txtprogressbar(file = stdout()))

y <- slow_sum(1:20)
```


### Jupyter bug #732 - handlers("progress") output is messy

Jupyter has other outputting issues. Specifically, Jupyter [injects an
_extra_ newline at the end of every
message](https://github.com/IRkernel/IRkernel/issues/732), e.g.

```r
> message("abc", appendLF = FALSE); message("def", appendLF = FALSE)
abc
def
> message("abc"); message("def")
abc

def

>
```

This causes any progress framework (e.g. the **progress** package)
that reports via messages to render progress output very poorly or not
at all.


## Design and Implementation

### Under the hood

When using the **progressr** package, progression updates are
communicated via R's condition framework, which provides methods for
creating, signaling, capturing, muffling, and relaying conditions.
Progression updates are of classes `progression` and
`immediateCondition`(\*).  The below figure gives an example how
progression conditions are created, signaled, and rendered.

(\*) The `immediateCondition` class of conditions are relayed as soon
as possible by the **[future]** framework, which means that
progression updates produced in parallel workers are reported to the
end user as soon as the main R session have received them.

![](imgs/slow_sum.svg)

_Figure: Sequence diagram illustrating how signaled progression
conditions are captured by `with_progress()`, or the global
progression handler, and relayed to the two progression handlers
'progress' (a progress bar in the terminal) and 'beepr' (auditory)
that the end user has chosen._


### Roadmap

Because this project is under active development, the progressr API is
currently kept at a very minimum.  This will allow for the framework
and the API to evolve while minimizing the risk for breaking code that
depends on it.  The roadmap for developing the API is roughly:

* [x] Provide minimal API for producing progress updates,
      i.e. `progressor()`, `with_progress()`, `handlers()`

* [x] Add support for global progress handlers removing the need for
      the user having to specify `with_progress()`, 
      i.e. `handlers(global = TRUE)` and `handlers(global = FALSE)`

* [ ] Make it possible to create a progressor also in the global
      environment (see 'Known Issues' above)

* [ ] Add support for nested progress updates

* [ ] Add API to allow users and package developers to design
      additional progression handlers

For a more up-to-date view on what features might be added, see
<https://github.com/futureverse/progressr/issues>.


[progressr]: https://progressr.futureverse.org
[future]: https://future.futureverse.org
[cli]: https://cran.r-project.org/package=cli
[crayon]: https://cran.r-project.org/package=crayon
