BUG FIX: plan(cluster, workers = parallelly::makeClusterSequential()) would erase the global environment as soon as a future is launched

Author: HenrikBengtsson

DESCRIPTION

@@ -1,5 +1,5 @@
 Package: future
-Version: 1.68.0-9035
+Version: 1.68.0-9036
 Title: Unified Parallel and Distributed Processing in R for Everyone
 Depends:
     R (>= 3.2.0)

NEWS.md

@@ -1,6 +1,6 @@
 # Version (development version)
 
-## Signifcant Changes
+## Significant Changes
 
  * Removed generic function `as.cluster()`, which has been re-exported
    from the **parallelly** package since 2020. If needed, please use
@@ -26,6 +26,9 @@
    1 unknown future arguments: 'interrupts'" for third-party future
    backends.
 
+ * `plan(cluster, workers = parallelly::makeClusterSequential())` would
+   erase the global environment as soon as a future is launched.
+
  * `resolved()` on a 'cluster' future would produce a warning when
    using a `parallelly::makeClusterSequential())` cluster.
 

R/backend_api-11.ClusterFutureBackend-class.R

@@ -283,8 +283,11 @@ launchFuture.ClusterFutureBackend <- function(backend, future, ...) {
   ##     may happen even if the future is evaluated inside a
   ##     local, e.g. local({ a <<- 1 }).
   ##     If the persistent = TRUE, this will be skipped.
+  ##
+  ##     SPECIAL CASE: Do not erase if a
+  ##     parallelly::makeClusterSequential() is used
   persistent <- isTRUE(future[["persistent"]])
-  if (!persistent) {
+  if (!persistent && !inherits(node, "sequential_node")) {
     if (debug) mdebug_push("eraseGlobalEnvironment() ...")
 
     t_start <- Sys.time()

inst/testme/test-makeClusterSequential.R

@@ -0,0 +1,33 @@
+if (getRversion() >= "4.4.0") {
+  library(future)
+  options(future.debug = FALSE)
+  
+  message("plan(cluster, workers = parallelly::makeClusterSequential()) ...")
+  cl <- parallelly::makeClusterSequential()
+  print(cl)
+  plan(cluster, workers = cl)
+  print(plan())
+
+  message("future(42)")
+  f <- future(42)
+  v <- value(f)
+  print(v)
+  stopifnot(v == 42)
+
+  message("future(2 * a, lazy = TRUE)")
+  a <- 42
+  f <- future(2 * a, lazy = TRUE)
+  rm(a)
+  v <- value(f)
+  print(v)
+  stopifnot(v == 2 * 42)
+
+  message("future(2 * a)")
+  a <- 42
+  f <- future(2 * a)
+  v <- value(f)
+  print(v)
+  stopifnot(v == 2 * a)
+
+  plan(sequential)
+}