src/library/utils/man/Rprof.Rd

% File src/library/utils/man/Rprof.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2018 R Core Team
% Distributed under GPL 2 or later

\name{Rprof}
\alias{Rprof}
\title{Enable Profiling of R's Execution}
\description{
  Enable or disable profiling of the execution of \R expressions.
}
\usage{
Rprof(filename = "Rprof.out", append = FALSE, interval = 0.02,
       memory.profiling = FALSE, gc.profiling = FALSE,
       line.profiling = FALSE, filter.callframes = FALSE,
       numfiles = 100L, bufsize = 10000L)
}
\arguments{
  \item{filename}{
    The file to be used for recording the profiling results.
    Set to \code{NULL} or \code{""} to disable profiling.
  }
  \item{append}{
    logical: should the file be over-written or appended to?
  }
  \item{interval}{
    real: time interval between samples.
  }
  \item{memory.profiling}{logical: write memory use information to the file?}
  \item{gc.profiling}{logical:  record whether GC is running?}
  \item{line.profiling}{logical:  write line locations to the file?}
  \item{filter.callframes}{logical: filter out intervening call frames
    of the call tree. See the filtering out call frames section.}
  \item{numfiles, bufsize}{integers: line profiling memory allocation}
}
\details{
  Enabling profiling automatically disables any existing profiling to
  another or the same file.

  Profiling works by writing out the call stack every \code{interval}
  seconds, to the file specified.  Either the \code{\link{summaryRprof}}
  function or the wrapper script \command{R CMD Rprof} can be used to
  process the output file to produce a summary of the usage; use
  \command{R CMD Rprof --help} for usage information.

  How time is measured varies by platform:
   \describe{
     \item{On Windows:}{
  Exactly what the time interval measures is subtle: it is time that the
  \R process is running and executing an \R command.  It is not however just
  CPU time, for if \code{readline()} is waiting for input, that counts
  (on Windows, but not on a Unix-alike).

  Note that the timing interval cannot be too small, for the time spent
  in each profiling step is added to the interval.  What is feasible is
  machine-dependent, but 10ms seemed as small as advisable on a 1GHz machine.
    }
    \item{On Unix-alikes}{it is the CPU
  time of the \R process, so for example excludes time when \R is waiting
  for input or for processes run by \code{\link{system}} to return.

  Note that the timing interval cannot usefully be too small: once the
  timer goes off, the information is not recorded until the next timing
  click (probably in the range 1--10 ms).
    }
  }

  Functions will only be recorded in the profile log if they put a
  context on the call stack (see \code{\link{sys.calls}}).  Some
  \link{primitive} functions do not do so: specifically those which are
  of \link{type} \code{"special"} (see the \sQuote{R Internals} manual
  for more details).

  Individual statements will be recorded in the profile log if
  \code{line.profiling} is \code{TRUE}, and if the code being executed
  was parsed with source references.  See \code{\link{parse}} for a
  discussion of source references.  By default the statement locations
  are not shown in \code{\link{summaryRprof}}, but see that help page
  for options to enable the display.
}

\section{Filtering Out Call Frames}{
  Lazy evaluation makes the call stack more complex because intervening
  call frames are created between the time arguments are applied to a
  function, and the time they are effectively evaluated. When the call
  stack is represented as a tree, these intervening frames appear as
  sibling nodes. For instance, evaluating \code{try(EXPR)} produces the
  following call tree, at the time \code{EXPR} gets evaluated:

\preformatted{
1. +-base::try(EXPR)
2. | \-base::tryCatch(...)
3. |   \-base:::tryCatchList(expr, classes, parentenv, handlers)
4. |     \-base:::tryCatchOne(expr, names, parentenv, handlers[[1L]])
5. |       \-base:::doTryCatch(return(expr), name, parentenv, handler)
6. \-EXPR
}

  Lines 2 to 5 are intervening call frames, the last of which finally
  triggered evaluation of \code{EXPR}. Setting \code{filter.callframes}
  to \code{TRUE} simplifies the profiler output by removing all sibling
  nodes of intervening frames.

  The same kind of call frame filtering is applied with \code{eval()}
  frames.  When you call \code{eval()}, two frames are pushed on the
  stack to ensure a continuity between frames. Say we have these
  definitions:

\preformatted{
calling <- function() evaluator(quote(called()), environment())
evaluator <- function(expr, env) eval(expr, env)
called <- function() EXPR()
}

  \code{calling()} calls \code{called()} in its own environment, via
  \code{eval()}. The latter is called indirectly through
  \code{evaluator()}. The net effect of this code is identical to just
  calling \code{called()} directly, without the intermediaries. However,
  the full call stack looks like this:


\preformatted{
1. calling()
2. \-evaluator(quote(called()), environment())
3.   \-base::eval(expr, env)
4.     \-base::eval(expr, env)
5.       \-called()
6.         \-EXPR()
}

  When call frame filtering is turned on, the true calling environment
  of \code{called()} is looked up, and the filtered call stack looks like
  this:

\preformatted{
1. calling()
5. \-called()
6.   \-EXPR()
}

  If the calling environment is not on the stack, the function called by
  \code{eval()} becomes a root node. Say we have:

\preformatted{
calling <- function() evaluator(quote(called()), new.env())
}

  With call frame filtering we then get the following filtered call
  stack:

\preformatted{
5. called()
6. \-EXPR()
}

}
\note{
  \describe{
    \item{On Unix-alikes:}{
  Profiling is not available on all platforms.  By default,
  support for profiling is compiled in if possible -- configure \R with
  \option{--disable-R-profiling} to change this.

  As \R profiling uses the same mechanisms as C profiling, the two
  cannot be used together, so do not use \code{Rprof} in an executable
  built for C-level profiling.
    }
    \item{On Windows:}{
  \code{filename} can be a UTF-8-encoded filepath that cannot be translated to
  the current locale.
    }
  }

The profiler interrupts R asynchronously, and it cannot allocate
memory to store results as it runs.  This affects line profiling,
which needs to store an unknown number of file pathnames.  The
\code{numfiles} and \code{bufsize} arguments control the size of
pre-allocated buffers to hold these results:  the former counts the
maximum number of paths, the latter counts the numbers of bytes in
them.  If the profiler runs out of space it will skip recording the
line information for new files, and issue a warning when
\code{Rprof(NULL)} is called to finish profiling.
}
\seealso{
  The chapter on \dQuote{Tidying and profiling R code} in
  \sQuote{Writing R Extensions} (see the \file{doc/manual} subdirectory
  of the \R source tree).

  \code{\link{summaryRprof}} to analyse the output file.

  \code{\link{tracemem}}, \code{\link{Rprofmem}} for other ways to track
  memory use.
}
\examples{
\dontrun{Rprof()
## some code to be profiled
Rprof(NULL)
## some code NOT to be profiled
Rprof(append = TRUE)
## some code to be profiled
Rprof(NULL)
## ...
## Now post-process the output as described in Details
}}
\keyword{utilities}