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\name{bpok}
\alias{bpok}
\alias{bperrorTypes}
\alias{bpresult}
\title{Resume computation with partial results}
\description{
Identifies unsuccessful results returned from \code{bplapply},
\code{bpmapply}, \code{bpvec}, \code{bpaggregate} or \code{bpvectorize}.
}
\usage{
bpok(x, type = bperrorTypes())
bperrorTypes()
bpresult(x)
}
\arguments{
\item{x}{
Results returned from a call to \code{bp*apply}.
}
\item{type}{
A character(1) error type, from the vector returned by
\code{bperrorTypes()} and described below
}
}
\details{
\code{bpok()} returns a \code{logical()} vector: FALSE for any jobs
that resulted in an error. \code{x} is the result list output by
\code{bplapply}, \code{bpmapply}, \code{bpvec}, \code{bpaggregate} or
\code{bpvectorize}.
\code{bperrorTypes()} returns a character() vector of possible error
types generated during parallel evaluation. Types are:
\itemize{
\item{\code{bperror}: Any of the following errors. This is the
default value for \code{bpok()}.}
\item{\code{remote_error}: An \emph{R} error occurring while
evaluating \code{FUN()}, e.g., taking the square root of a
character vector, \code{sqrt("One")}.}
\item{\code{unevaluated_error}: When \code{*Param(stop.on.error =
TRUE)} (default), a remote error halts evaluation of other
tasks assigned to the same worker. The return value for these
unevaluated elements is an error of type
\code{unevaluated_error}.}
\item{\code{not_available_error}: Only produced by
\code{DoparParam()} when a remote error occurs during evaluation
of an element of \code{X} -- \code{DoparParam()} sets all values
after the remote error to this class.}
\item{\code{worker_comm_error}: An error occurring while trying to
communicate with workers, e.g., when a worker quits unexpectedly.
when this type of error occurs, the length of the result may
differ from the length of the input \code{X}.
}
}
\code{bpresult()} when applied to an object with a class of one of the
error types returns the list of tasks results.
}
\author{Michel Lang, Martin Morgan, Valerie Obenchain, and Jiefei Wang}
\seealso{
\code{\link{tryCatch}}
}
\examples{
## -----------------------------------------------------------------------
## Catch errors:
## -----------------------------------------------------------------------
## By default 'stop.on.error' is TRUE in BiocParallelParam objects. If
## 'stop.on.error' is TRUE an ill-fated bplapply() simply stops,
## displaying the error message.
param <- SnowParam(workers = 2, stop.on.error = TRUE)
result <- tryCatch({
bplapply(list(1, "two", 3), sqrt, BPPARAM = param)
}, error=identity)
result
class(result)
bpresult(result)
## If 'stop.on.error' is FALSE then the computation continues. Errors
## are signalled but the full evaluation can be retrieved
param <- SnowParam(workers = 2, stop.on.error = FALSE)
X <- list(1, "two", 3)
result <- bptry(bplapply(X, sqrt, BPPARAM = param))
result
## Check for errors:
fail <- !bpok(result)
fail
## Access the traceback with attr():
tail(attr(result[[2]], "traceback"), 5)
## -----------------------------------------------------------------------
## Resume calculations:
## -----------------------------------------------------------------------
## The 'resume' mechanism is triggered by supplying a list of partial
## results as 'BPREDO'. Data elements that failed are rerun and merged
## with previous results.
## A call of sqrt() on the character "2" returns an error. Fix the input
## data by changing the character "2" to a numeric 2:
X_mod <- list(1, 2, 3)
bplapply(X_mod, sqrt, BPPARAM = param , BPREDO = result)
}
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