Package: future
===============

Version: 1.8.0 [2018-04-08]

SIGNIFICANT CHANGES:

 o Errors produces when evaluating futures are now (re-)signaled on the master
   R process "as is" with the original content and class attributes.
 
NEW FEATURES:

 o More errors related to orchestration of futures are of class FutureError to
   make it easier to distinguish them from future evaluation errors.
   
 o Add support for a richer set of results returned by resolved futures.
   Previously only the value of the future expression, which could be a
   captured error to be resignaled, was expected. Now a FutureResult object
   may be returned instead.  Although not supported in this release, this
   update opens up for reporting on additional information from the evaluation
   of futures, e.g. captured output, timing and memory benchmarks etc. Before
   that can take place, existing future backend packages will have to be
   updated accordingly.

 o backtrace() returns only the last call that produced the error.  It is
   unfortunately not possible to capture the call stack that led up to the
   error when evaluating a future expression.
   
BUG FIXES:

 o value() for MulticoreFuture would not produce an error when a (forked)
   background R workers would terminate before the future expression is
   resolved.  This was a limitation inherited from the parallel package.
   Now an informative FutureError message is produced.

 o value() for MulticoreFuture would not signal errors unless they inherited
   from 'simpleError' - now it's enough for them to inherits from 'error'.

 o value() for ClusterFuture no longer produces a FutureEvaluationError, but
   FutureError, if the connection to the R worker has changed (which happens
   if something as drastic as closeAllConnections() have been called.)

 o futureCall(..., globals = FALSE) would produce "Error: second argument must
   be a list", because the explicit arguments where not exported.  This could
   also happen when specifying globals by name or as a named list.

 o Nested futures were too conservative in requiring global variables to exist,
   even when they were false positives.

DEPRECATED AND DEFUNCT:

 o future::future_lapply() is formally deprecated. Please use the one in the
   future.apply package instead.
  
 o Recently introduced FutureEvaluationCondition classes are deprecated,
   because they no longer serve a purpose since future evaluation conditions
   are now signaled as is.
   

Version: 1.7.0 [2018-02-10]

SIGNIFICANT CHANGES:

 o future_lapply() has moved to the future.apply package available on CRAN.

NEW FEATURES:

 o Argument 'workers' of future strategies may now also be a function, which
   is called without argument when the future strategy is set up and used as
   is.  For instance, plan(multiprocess, workers = halfCores) where
   halfCores <- function() { max(1, round(availableCores() / 2)) } will use
   half of the number of available cores.  This is useful when using nested
   future strategies with remote machines.
 
 o On Windows, makeClusterPSOCK(), and therefore plan(multisession) and
   plan(multiprocess), will use the SSH client distributed with RStudio as
   a fallback if neither 'ssh' nor 'plink' is available on the system PATH.

 o Now plan() makes sure that nbrOfWorkers() will work for the new strategy.
   This will help catch mistakes such as plan(cluster, workers = cl) where
   'cl' is a basic R list rather than a 'cluster' list early on.

 o Added %packages% to explicitly control packages to be attached when a
   future is resolved, e.g. y %<-% { YT[2] } %packages% "data.table".
   Note, this is only needed in cases where the automatic identification of
   global and package dependencies is not sufficient.

 o Added condition classes FutureCondition, FutureMessage, FutureWarning, and
   FutureError representing conditions that occur while a future is setup,
   launched, queried, or retrieved.  They do *not* represent conditions that
   occur while evaluating the future expression.  For those conditions, new
   classes FutureEvaluationCondition, FutureEvaulationMessage,
   FutureEvaluationWarning, and FutureEvaluationError exists.

DOCUMENTATION:

 o Vignette 'Common Issues with Solutions' now documents the case where the
   future framework fails to identify a variable as being global because it
   is only so conditionally, e.g. 'if (runif(1) < 1/2) x <- 0; y <- 2 * x'.

BETA FEATURES:

 o Added mechanism for detecting globals that _may_ not be exportable to an
   external R process (a "worker").  Typically, globals that carry connections
   and external pointers ("externalptr") can not be exported, but there are
   exceptions.  By setting options 'future.globals.onReference' to "warning",
   a warning is produced informing the user about potential problems.  If
   "error", an error is produced.  Because there might be false positive, the
   default is "ignore", which will cause above scans to be skipped.  If there
   are non-exportable globals and these tests are skipped, a run-time error
   may be produced only when the future expression is evaluated.

BUG FIXES:

 o The total size of global variables was overestimated, and dramatically so
   if defined in the global environment and there were are large objects there
   too.  This would sometimes result in a false error saying that the total
   size is larger than the allowed limit.

 o An assignment such as 'x <- x + 1' where the left-hand side (LHS) 'x' is a
   global failed to identify 'x' as a global because the right-hand side (RHS)
   'x' would override it as a local variable.  Updates to the globals package
   fixed this problem.

 o makeClusterPSOCK(..., renice = 19) would launch each PSOCK worker via
   'nice +19' resulting in the error "nice: '+19': No such file or directory".
   This bug was inherited from parallel::makePSOCKcluster().  Now using
   'nice --adjustment=19' instead.

 o Protection against passing future objects to other futures did not work
   for future strategy 'multicore'.
 
DEPRECATED AND DEFUNCT:

 o future_lapply() has moved to the new future.apply package available on CRAN.
   The future::future_lapply() function will soon be deprecated, then defunct,
   and eventually be removed from the future package. Please update your code
   to make use of future.apply::future_lapply() instead.
   
 o Dropped defunct 'eager' and 'lazy' futures; use 'sequential' instead.

 o Dropped defunct arguments 'cluster' and 'maxCores'; use 'workers' instead.

 o In previous version of the future package the FutureError class was used
   to represent both orchestration errors (now FutureError) and evaluation
   errors (now FutureEvaluationError).  Any usage of class FutureError for
   the latter type of errors is deprecated and should be updated to
   FutureEvaluationError.


Version: 1.6.2 [2017-10-16]

NEW FEATURES:

 o Now plan() accepts also strings such as "future::cluster".

 o Now backtrace(x[[ER]]) works also for non-environment 'x':s, e.g. lists.

BUG FIXES:

 o When measuring the size of globals by scanning their content, for certain
   types of classes the inferred lengths of these objects were incorrect
   causing internal subset out-of-range issues.

 o print() for Future would output one global per line instead of
   concatenating the information with commas.


Version: 1.6.1 [2017-09-08]

NEW FEATURES:

 o Now exporting getGlobalsAndPackages().

BUG FIXES:

 o future_lapply() would give "Error in objectSize.env(x, depth = depth - 1L):
   object 'nnn' not found" when for instance 'nnn' is part of an unresolved
   expression that is an argument value.

SOFTWARE QUALITY:

 o FIX: Some of the package assertion tests made too precise assumptions about
   the object sizes, which fails with the introduction of ALTREP in R-devel
   which causes the R's SEXP header size to change.
 

Version: 1.6.0 [2017-08-11]

NEW FEATURES:

 o Now tweak(), and hence plan(), generates a more informative error message if
   a non-future function is specified by mistake, e.g. calling plan(cluster)
   with the 'survival' package attached after 'future' is equivalent to calling
   plan(survival::cluster) when plan(future::cluster) was intended.

BUG FIXES:

 o nbrOfWorkers() gave an error with plan(remote). Fixed by making the 'remote'
   future inherit 'cluster' (as it should).

SOFTWARE QUALITY:

 o TESTS: No longer testing forced termination of forked cluster workers when
   running on Solaris. The termination was done by launching a future that
   called quit(), but that appeared to have corrupted the main R session when
   running on Solaris.

DEPRECATED AND DEFUNCT:

 o Formally defunct 'eager' and 'lazy' futures; use 'sequential' instead.

 o Dropped previously defunct %<=% and %=>% operators.
 

Version: 1.5.0 [2017-05-24]

SIGNIFICANT CHANGES:

 o Multicore and multisession futures no longer reserve one core for the
   main R process, which was done to lower the risk for producing a higher
   CPU load than the number of cores available for the R session.
 
NEW FEATURES:

 o makeClusterPSOCK() now defaults to use the Windows PuTTY software's SSH
   client 'plink -ssh', if 'ssh' is not found.

 o Argument 'homogeneous' of makeNodePSOCK(), a helper function of
   makeClusterPSOCK(), will default to FALSE also if the hostname is a
   fully qualified domain name (FQDN), that is, it "contains periods".
   For instance, c('node1', 'node2.server.org') will use homogeneous = TRUE
   for the first worker and homogeneous = FALSE for the second.

 o makeClusterPSOCK() now asserts that each cluster node is functioning by
   retrieving and recording the node's session information including the
   process ID of the corresponding R process.

 o Nested futures sets option 'mc.cores' to prevent spawning of recursive
   parallel processes by mistake.  Because 'mc.cores' controls _additional_
   processes, it was previously set to zero.  However, since some functions
   such as mclapply() does not support that, it is now set to one instead.   

DOCUMENTATION:

 o Help on makeClusterPSOCK() gained more detailed descriptions on arguments
   and what their defaults are.
 
DEPRECATED AND DEFUNCT:

 o Formally deprecated eager futures; use sequential instead.

BUG FIXES:

 o future_lapply() with multicore / multisession futures, would use a
   suboptimal workload balancing where it split up the data in one chunk too
   many.  This is no longer a problem because of how argument 'workers' is
   now defined for those type of futures (see note on top).
 
 o future_lapply(), as well as lazy multicore and lazy sequential futures, did
   not respect option 'future.globals.resolve', but was hardcoded to always
   resolve globals (future.globals.resolve = TRUE).

 o When globals larger than the allowed size (option 'future.globals.maxSize')
   are detected an informative error message is generated.  Previous version
   introduced a bug causing the error to produce another error.

 o Lazy sequential futures would produce an error when resolved if required
   packages had been detached.

 o print() would not display globals gathered for lazy sequential futures.

SOFTWARE QUALITY:

 o Added package tests for globals part of formulas part of other globals,
   e.g. purrr::map(x, ~ rnorm(.)), which requires globals (>= 0.10.0).

 o Now package tests with parallel::makeCluster() not only test for
   type = 'PSOCK' clusters but also 'FORK' (when supported).

 o TESTS: Cleaned up test scripts such that the overall processing time for
   the tests was roughly halved, while preserving the same test coverage.
 

Version: 1.4.0 [2017-03-12]

SIGNIFICANT CHANGES:

 o The default for future_lapply() is now to _not_ generate RNG seeds
   (future.seed = FALSE).  If proper random number generation is needed,
   use future.seed = TRUE.  For more details, see help page.
   
NEW FEATURES:

 o future() and future_lapply() gained argument 'packages' for explicitly
   specifying packages to be attached when the futures are evaluated.
   Note that the default throughout the future package is that all globals
   and all required packages are automatically identified and gathered, so
   in most cases those do not have to be specified manually.

 o The default values for arguments 'connectTimeout' and 'timeout' of
   makeNodePSOCK() can now be controlled via global options.

RANDOM NUMBER GENERATION:

 o Now future_lapply() guarantees that the RNG state of the calling R process
   after returning is updated compared to what it was before and in the exact
   same way regardless of 'future.seed' (except FALSE), 'future.scheduling'
   and future strategy used.  This is done in order to guarantee that an R
   script calling future_lapply() multiple times should be numerically
   reproducible given the same initial seed.

 o It is now possible to specify a pre-generated sequence of .Random.seed
   seeds to be used for each FUN(x[i], ...) call in future_lapply(x, FUN, ...).

PERFORMANCE:

 o future_lapply() scans global variables for non-resolved futures (to resolve
   them) and calculate their total size once.  Previously, each chunk
   (a future) would redo this.

BUG FIX:

 o Now future_lapply(x, FUN, ...) identifies global objects among 'x', 'FUN'
   and '...' recursively until no new globals are found.  Previously, only
   the first level of globals were scanned.  This is mostly thanks to a bug
   fix in globals 0.9.0.

 o A future that used a global object 'x' of a class that overrides length()
   would produce an error if length(x) reports more elements than what can
   be subsetted.

 o nbrOfWorkers() gave an error with plan(cluster, workers = cl) where
   'cl' is a cluster object created by parallel::makeCluster() etc.
   This prevented for instance future_lapply() to work with such setups.

 o plan(cluster, workers = cl) where cl <- makeCluster(..., type = MPI") 
   would give an instant error due to an invalid internal assertion.

DEPRECATED AND DEFUNCT:

 o Previously deprecated arguments 'maxCores' and 'cluster' are now defunct.

 o Previously deprecated assignment operators %<=% and %=>% are now defunct.

 o availableCores(method = "mc.cores") is now defunct in favor of "mc.cores+1".


Version: 1.3.0 [2017-01-18]

SIGNIFICANT CHANGES:

 o Where applicable, workers are now initiated when calling plan(), e.g.
   plan(cluster) will set up workers on all cluster nodes.  Previously,
   this only happened when the first future was created.

NEW FEATURES:

 o Renamed 'eager' futures to 'sequential', e.g. plan(sequential).
   The 'eager' futures will be deprecated in an upcoming release.
   
 o Added support for controlling whether a future is resolved eagerly
   or lazily when creating the future, e.g. future(..., lazy = TRUE)
   futureAssign(..., lazy = TRUE), and x %<-% { ... } %lazy% TRUE.

 o future(), futureAssign() and futureCall() gained argument 'seed',
   which specifies a L'Ecuyer-CMRG random seed to be used by the future.
   The seed for future assignment can be specified via %seed%.
   
 o futureAssign() now passes all additional arguments to future().

 o Added future_lapply() which supports load balancing ("chunking")
   and perfect reproducibility (regardless of type of load balancing
   and how futures are resolved) via initial random seed.
 
 o Added availableWorkers().  By default it returns localhost workers
   according to availableCores().  In addition, it detects common
   HPC allocations given in environment variables set by the HPC
   scheduler.
   
 o The default for plan(cluster) is now workers = availableWorkers().
 
 o Now plan() stops any clusters that were implicitly created. For
   instance, a multisession cluster created by plan(multisession) will
   be stopped when plan(eager) is called.

 o makeClusterPSOCK() treats workers that refer to a local machine by
   its local or canonical hostname as "localhost".  This avoids having
   to launch such workers over SSH, which may not be supported on all
   systems / compute cluster.

 o Option 'future.debug' = TRUE also reports on total size of
   globals identified and for cluster futures also the size of the
   individual global variables exported.

 o Option 'future.wait.timeout' (replaces 'future.wait.times') specifies
   the maximum waiting time for a free workers (e.g. a core or a
   compute node) before generating a timeout error.  

 o Option 'future.availableCores.fallback', which defaults to environment
   variable 'R_FUTURE_AVAILABLECORES_FALLBACK' can now be used to specify
   the default number of cores / workers returned by availableCores()
   and availableWorkers() when no other settings are available.  For
   instance, if R_FUTURE_AVAILABLECORES_FALLBACK=1 is set system wide
   in an HPC environment, then all R processes that uses availableCores()
   to detect how many cores can be used will run as single-core processes.
   Without this fallback setting, and without other core-specifying settings,
   the default will be to use all cores on the machine, which does not play
   well on multi-user systems.

GLOBALS:

 o Globals part of locally defined functions are now also identified
   thanks to globals (>= 0.8.0) updates.
   
DEPRECATED AND DEFUNCT:

 o Lazy futures and plan(lazy) are now deprecated. Instead, use plan(eager)
   and then f <- future(..., lazy = TRUE) or x %<-% { ... } %lazy% TRUE.
   The reason behind this is that in some cases code that uses futures
   only works under eager evaluation (lazy = FALSE; the default), or vice
   verse. By removing the "lazy" future strategy, the user can no longer
   override the lazy = TRUE / FALSE that the developer is using.  
 
BUG FIXES:

 o Creation of cluster futures (including multisession ones) would
   time out already after 40 seconds if all workers were busy.
   New default timeout is 30 days (option 'future.wait.timeout').

 o nbrOfWorkers() gave an error for plan(cluster, workers) where 'workers'
   was a character vector or a 'cluster' object of the parallel package.
   Because of this, future_lapply() gave an error with such setups.

 o availableCores(methods = "_R_CHECK_LIMIT_CORES_") would give an error
   if not running R CMD check.
   
    
Version: 1.2.0 [2016-11-12]

NEW FEATURES:

 o Added makeClusterPSOCK() - a version of parallel::makePSOCKcluster()
   that allows for more flexible control of how PSOCK cluster workers
   are set up and how they are launched and communicated with if running
   on external machines.

 o Added generic as.cluster() for coercing objects to cluster objects
   to be used as in plan(cluster, workers = as.cluster(x)).  Also added
   a c() implementation for cluster objects such that multiple cluster
   objects can be combined into a single one.

 o Added sessionDetails() for gathering details of the current R session.

 o plan() and plan("list") now prints more user-friendly output.

 o On Unix, internal myInternalIP() tries more alternatives for finding
   the local IP number.

DEPRECATED AND DEFUNCT:

 o %<=% is deprecated. Use %<-% instead. Same for %=>%.
    
BUG FIXES:

 o values() for lists and list environments of futures where one or more
   of the futures resolved to NULL would give an error.

 o value() for ClusterFuture would give cryptic error message
   "Error in stop(ex) : bad error message" if the cluster worker had
   crashed / terminated.  Now it will instead give an error message like
   "Failed to retrieve the value of ClusterFuture from cluster node #1 on
   'localhost'. The reason reported was "error reading from connection".

 o Argument 'user' to remote() was ignored (since 1.1.0).
    
    
Version: 1.1.1 [2016-10-10]

BUG FIXES:

 o For the special case where 'remote' futures use workers = "localhost"
   they (again) use the exact same R executable as the main / calling R
   session (in all other cases it uses whatever 'Rscript' is found in the
   PATH).  This was already indeed implemented in 1.0.1, but with the
   added support for reverse SSH tunnels in 1.1.0 this default behavior
   was lost.
    
    
Version: 1.1.0 [2016-10-09]

NEW FEATURES:

 o REMOTE CLUSTERS: It is now very simple to use cluster() and remote()
   to connect to remote clusters / machines.  As long as you can connect
   via ssh to those machines, it works also with these future.  The new
   code completely avoids incoming firewall and incoming port forwarding
   issues previously needed.  This is done by using reverse SSH tunneling.
   There is also no need to worry about internal or external IP numbers.

 o Added optional argument 'label' to all futures, e.g.
   f <- future(42, label="answer") and v %<-% { 42 } %label% "answer".

 o Added argument 'user' to cluster() and remote().

 o Now all Future classes supports run() for launching the future and
   value() calls run() if the future has not been launched.

 o MEMORY: Now plan(cluster, gc=TRUE) causes the background
   R session to be garbage collected immediately after the value
   is collected.  Since multisession and remote futures are special
   cases of cluster futures, the same is true for these as well.

 o ROBUSTNESS: Now the default future strategy is explicitly set when
   no strategies are set, e.g. when used nested futures.  Previously,
   only mc.cores was set so that only a single core was used, but now
   also plan("default") set.

 o WORKAROUND: resolved() on cluster futures would block on Linux until
   future was resolved.  This is due to a bug in R.  The workaround is
   to use round the timeout (in seconds) to an integer, which seems to
   always work / be respected.

GLOBALS:

 o Global variables part of subassignments in future expressions
   are recognized and exported (iff found), e.g. x$a <- value,
   x[["a"]] <- value, and x[1,2,3] <- value.

 o Global variables part of formulae in future expressions are
   recognized and exported (iff found), e.g. y ~ x | z.

 o As an alternative to the default automatic identification of
   globals, it is now also possible to explicitly specify them either
   by their names (as a character vector) or by their names and values
   (as a named list), e.g. f <- future({ 2*a }, globals=c("a")) or
   f <- future({ 2*a }, globals=list(a=42)).  For future assignments one
   can use the %globals% operator, e.g. y %<-% { 2*a } %globals% c("a").

DOCUMENTATION:

 o Added vignette on command-line options and other methods for
   controlling the default type of futures to use.
    
    
Version: 1.0.1 [2016-07-04]

 o ROBUSTNESS: For the special case where 'remote' futures use
   workers = "localhost" they now use the exact same R executable
   as the main / calling R session (in all other cases it uses
   whatever 'Rscript' is found in the PATH).

 o FutureError now extends simpleError and no longer the error
   class of captured errors.

DOCUMENTATION:

 o Adding section to vignette on globals in formulas describing how
   they are currently not automatically detected and how to explicitly
   export them.

BUG FIXES:
  
 o Since future 0.13.0, a global 'pkg' would be overwritten by the
   name of the last package attached in future.

 o Futures that generated R.oo::Exception errors, they triggered
   another internal error.
   
    
Version: 1.0.0 [2016-06-24]

NEW FEATURES:

 o Add support for remote(..., myip="<external>"), which now
   queries a set of external lookup services in case one of them
   fails.

 o Add mandelbrot() function used in demo to the API for convenience.

 o ROBUSTNESS: If .future.R script, which is sourced when the future
   package is attached, gives an error, then the error is ignored
   with a warning.

 o TROUBLESHOOTING: If the future requires attachment of packages,
   then each namespace is loaded separately and before attaching
   the package.  This is done in order to see the actual error
   message in case there is a problem while loading the namespace.
   With require()/library() this error message is otherwise suppressed
   and replaced with a generic one.

GLOBALS:

 o Falsely identified global variables no longer generate
   an error when the future is created.  Instead, we leave it to R
   and the evaluation of the individual futures to throw an error
   if the a global variable is truly missing.  This was done in order
   to automatically handle future expressions that use non-standard
   evaluation (NSE), e.g. subset(df, x < 3) where 'x' is falsely
   identified as a global variable.

 o Dropped support for system environment variable 'R_FUTURE_GLOBALS_MAXSIZE'.

DOCUMENTATION:

 o DEMO: Now the Mandelbrot demo tiles a single Mandelbrot region
   with one future per tile. This better illustrates parallelism.

 o Documented R options used by the future package.
    
BUG FIXES:

 o Custom futures based on a constructor function that
   is defined outside a package gave an error.

 o plan("default") assumed that the 'future.plan' option
   was a string; gave an error if it was a function.

 o Various future options were not passed on to futures.

 o A startup .future.R script is no longer sourced if the
   future package is attached by a future expression.
    
    
Version: 0.15.0 [2016-06-13]

NEW FEATURES:

 o Added remote futures, which are cluster futures with convenient
   default arguments for simple remote access to R, e.g.
   plan(remote, workers="login.my-server.org").

 o Now .future.R (if found in the current directory or otherwise in
   the user's home directory) is sourced when the future package is
   attach (but not loaded).  This helps separating scripts from
   configuration of futures.

 o Added support for plan(cluster, workers=c("n1", "n2", "n2", "n4")),
   where 'workers' (also for ClusterFuture()) is a set of host names
   passed to parallel::makeCluster(workers).  It can also be the number
   of localhost workers.

 o Added command line option --parallel=<p>, which is long for -p <p>.

 o Now command line option -p <p> also set the default future strategy
   to multiprocessing (if p >= 2 and eager otherwise), unless another
   strategy is already specified via option 'future.plan' or system
   environment variable R_FUTURE_PLAN.

 o Now availableCores() also acknowledges environment variable NSLOTS
   set by Sun/Oracle Grid Engine (SGE).

 o MEMORY: Added argument 'gc=FALSE' to all futures.  When TRUE, the
   garbage collector will run at the very end in the process that
   evaluated the future (just before returning the value).  This may
   help lowering the overall memory footprint when running multiple
   parallel R processes.  The user can enable this by specifying
   plan(multiprocess, gc=TRUE).  The developer can control this using
   future(expr, gc=TRUE) or v %<-% { expr } %tweak% list(gc=TRUE).

PERFORMANCE:

 o Significantly decreased the overhead of creating a future, particularly
   multicore futures.
    
BUG FIXES: 

 o Future would give an error with plan(list("eager")),
   whereas it did work with plan("eager") and plan(list(eager)).
    
    
Version: 0.14.0 [2016-05-16]

NEW FEATURES:

 o Added nbrOfWorkers().

 o Added informative print() method for the Future class.

 o values() passes arguments '...' to value() of each Future.

 o Added FutureError class.

DEPRECATED AND DEFUNCT:

 o Renamed arguments 'maxCores' and 'cluster' to 'workers'.  If using
   the old argument names a deprecation warning will be generated, but
   it will still work until made defunct in a future release.
    
BUG FIXES:

 o resolve() for lists and environments did not work
   properly when the set of futures was not resolved in order,
   which could happen with asynchronous futures.
    
    
Version: 0.13.0 [2016-04-13]

NEW FEATURES:

 o Add support to plan() for specifying different future strategies for
   the different levels of nested futures.

 o Add backtrace() for listing the trace the expressions evaluated (the
   calls made) before a condition was caught.

 o Add transparent futures, which are eager futures with early signaling
   of conditioned enabled and whose expression is evaluated in the calling
   environment.  This makes the evaluation of such futures as similar
   as possible to how R evaluates expressions, which in turn simplifies
   troubleshooting errors etc.

 o Add support for early signaling of conditions.  The default is
   (as before) to signal conditions when the value is queried.
   In addition, they may be signals as soon as possible, e.g. when
   checking whether a future is resolved or not.

 o Signaling of conditions when calling value() is now controlled by
   argument 'signal' (previously 'onError').

 o Now UniprocessFuture:s captures the call stack for errors occurring
   while resolving futures.

 o ClusterFuture gained argument 'persistent=FALSE'.  With persistent=TRUE,
   any objects in the cluster R session that was created during the
   evaluation of a previous future is available for succeeding futures
   that are evaluated in the same session.  Moreover, globals are
   still identified and exported but "missing" globals will not give
   an error - instead it is assumed such globals are available in the
   environment where the future is evaluated.

 o OVERHEAD: Utility functions exported by ClusterFuture are now much
   smaller; previously they would export all of the package environment.
    
BUG FIXES:
  
 o f <- multicore(NA, maxCores=2) would end up in an endless
   waiting loop for a free core if availableCores() returned one.

 o ClusterFuture would ignore local=TRUE.
    
    
Version: 0.12.0 [2016-02-23]

NEW FEATURES:

 o Added multiprocess futures, which are multicore futures if supported,
   otherwise multisession futures.  This makes it possible to use
   plan(multiprocess) everywhere regardless of operating system.

 o Future strategy functions gained class attributes such that it is
   possible to test what type of future is currently used, e.g.
   inherits(plan(), "multicore").

 o ROBUSTNESS: It is only the R process that created a future that can
   resolve it. If a non-resolved future is queried by another R process,
   then an informative error is generated explaining that this is not
   possible.

 o ROBUSTNESS: Now value() for multicore futures detects if the underlying
   forked R process was terminated before completing and if so generates
   an informative error messages.

PERFORMANCE:

 o Adjusted the parameters for the schema used to wait for next available
   cluster node such that nodes are polled more frequently.

GLOBALS:

 o resolve() gained argument 'recursive'.

 o Added option 'future.globals.resolve' for controlling whether
   global variables should be resolved for futures or not.  If TRUE, then
   globals are searched recursively for any futures and if found such
   "global" futures are resolved.  If FALSE, global futures are not
   located, but if they are later trying to be resolved by the parent
   future, then an informative error message is generated clarifying
   that only the R process that created the future can resolve it.
   The default is currently FALSE.

BUG FIX:

 o FIX: Exports of objects available in packages already attached
   by the future were still exported.

 o FIX: Now availableCores() returns 3L (=2L+1L) instead of 2L
   if _R_CHECK_LIMIT_CORES_ is set.
    
    
Version: 0.11.0 [2016-01-15]

NEW FEATURES:

 o Add multisession futures, which analogously to multicore ones,
   use multiple cores on the local machine with the difference
   that they are evaluated in separate R session running in the
   background rather than separate forked R processes.
   A multisession future is a special type of cluster futures that
   do not require explicit setup of cluster nodes.

 o Add support for cluster futures, which can make use of a cluster
   of nodes created by parallel::makeCluster().

 o Add futureCall(), which is for futures what do.call() is otherwise.

 o Standardized how options are named, i.e. 'future.<option>'.
   If you used any future options previously, make sure to check
   they follow the above format.

GLOBALS:

 o All futures now validates globals by default (globals=TRUE).
   
    
Version: 0.10.0 [2015-12-30]

NEW FEATURES:

 o Now %<=% can also assign to multi-dimensional list environments.

 o Add futures(), values() and resolved().

 o Add resolve() to resolve futures in lists and environments.

 o Now availableCores() also acknowledges the number of CPUs
   allotted by Slurm.

 o CLEANUP: Now the internal future variable created by %<=% is
   removed when the future variable is resolved.
    
BUG FIXES:  

 o futureOf(envir=x) did not work properly when 'x' was
   a list environment.
    
    
Version: 0.9.0 [2015-12-11]

NEW FEATURES:

 o ROBUSTNESS: Now values of environment variables are trimmed
   before being parsed.

 o ROBUSTNESS: Add reproducibility test for random number
   generation using Pierre L'Ecuyer's RNG stream regardless
   of how futures are evaluated, e.g. eager, lazy and multicore.

GLOBALS:

 o Now globals ("unknown" variables) are identified using the
   new findGlobals(..., method="ordered") in globals (> 0.5.0)
   such that a global variable preceding a local variable with
   the same name is properly identified and exported/frozen.

DOCUMENTATION:

 o Updated vignette on common issues with the case where a global
   variable is not identified because it is hidden by an element
   assignment in the future expression.
    
BUG FIXES:
 
 o Errors occurring in multicore futures could prevent
   further multicore futures from being created.
    
    
Version: 0.8.2 [2015-10-14]
    
BUG FIXES:
  
 o Globals that were copies of package objects were not exported to the
   future environments.

 o The future package had to be attached or future::future() had to be
   imported, if %<=% was used internally in another package.
   Similarly, it also had to be attached if multicore futures where used.
    
    
Version: 0.8.1 [2015-10-05]

DOCUMENTATION:

 o Added vignette 'Futures in R: Common issues with solutions'.

GLOBALS:

 o eager() and multicore() gained argument 'globals', where
   globals=TRUE will validate that all global variables
   identified can be located already before the future is
   created.  This provides the means for providing the same
   tests on global variables with eager and multicore futures
   as with lazy futures.

BUG FIXES:

 o lazy(sum(x, ...), globals=TRUE) now properly passes `...`
   from the function from which the future is setup.  If not
   called within a function or called within a function without
   `...` arguments, an informative error message is thrown.
    
    
Version: 0.8.0 [2015-09-06]

NEW FEATURES:

 o plan("default") resets to the default strategy, which is
   synchronous eager evaluation unless option 'future_plan'
   or environment variable 'R_FUTURE_PLAN' has been set.

 o availableCores("mc.cores") returns getOption("mc.cores") + 1L,
   because option 'mc.cores' specifies "allowed number of _additional_
   R processes" to be used in addition to the main R process.
    
BUG FIXES:

 o plan(future::lazy) and similar gave errors.
    
    
Version: 0.7.0 [2015-07-13]

NEW FEATURES:

 o multicore() gained argument 'maxCores', which makes it
   possible to use for instance plan(multicore, maxCores=4L).

 o Add availableMulticore() [from (in-house) 'async' package].

DOCUMENTATION:

 o More colorful demo("mandelbrot", package="future").
    
BUG FIXES:
  
 o ROBUSTNESS: multicore() blocks until one of the CPU cores
   is available, iff all are currently occupied by other
   multicore futures.

 o old <- plan(new) now returns the old plan/strategy
   (was the newly set one).
    
    
Version: 0.6.0 [2015-06-18]

NEW FEATURES:

 o Add multicore futures, which are futures that are resolved
   asynchronously in a separate process.  These are only
   supported on Unix-like systems, but not on Windows.
    
    
Version: 0.5.1 [2015-06-18]

NEW FEATURES:

 o Eager and lazy futures now records the result internally
   such that the expression is only evaluated once, even if
   their errored values are requested multiple times.

 o Eager futures are always created regardless of error or not.

 o All Future objects are environments themselves that record
   the expression, the call environment and optional variables.
    
    
Version: 0.5.0 [2015-06-16]

GLOBALS:

 o lazy() "freezes" global variables at the time when
   the future is created.  This way the result of a lazy
   future is more likely to be the same as an eager future.
   This is also how globals are likely to be handled by
   asynchronous futures.
    
    
Version: 0.4.2 [2015-06-15]

NEW FEATURES:

 o plan() records the call.

DOCUMENTATION:

 o Added demo("mandelbrot", package="future"), which can be
   re-used by other future packages.
    
    
Version: 0.4.1 [2015-06-14]

NEW FEATURES:

 o Added plan().

 o Added eager future - useful for troubleshooting.
    
    
Version: 0.4.0 [2015-06-07]

 o Distilled Future API from (in-house) 'async' package.
