From 063ec92c94281c6c1a7c9f35005266e496b3e5dd Mon Sep 17 00:00:00 2001
From: Henrik Bengtsson <henrik.bengtsson@gmail.com>
Date: Fri, 19 Jan 2024 13:25:21 -0800
Subject: [PATCH 1/2] PERFORMANCE: Avoid passing down top-level future strategy
 (i.e. plan('next')) to future. This avoids some data-transfer overhead that
 may happen for some strategies [#713]

---
 DESCRIPTION      |  4 ++--
 R/Future-class.R | 24 ++++++++++++++----------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/DESCRIPTION b/DESCRIPTION
index 817f8d70..11ff2b2e 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,5 +1,5 @@
 Package: future
-Version: 1.33.1
+Version: 1.33.1-9001
 Title: Unified Parallel and Distributed Processing in R for Everyone
 Imports:
     digest,
@@ -39,5 +39,5 @@ LazyLoad: TRUE
 ByteCompile: TRUE
 URL: https://future.futureverse.org, https://github.com/HenrikBengtsson/future
 BugReports: https://github.com/HenrikBengtsson/future/issues
-RoxygenNote: 7.2.3
+RoxygenNote: 7.3.0
 Roxygen: list(markdown = TRUE)
diff --git a/R/Future-class.R b/R/Future-class.R
index 479eb5ce..78386d17 100644
--- a/R/Future-class.R
+++ b/R/Future-class.R
@@ -736,9 +736,15 @@ getExpression.Future <- local({
   tmpl_enter_plan <- bquote_compile({
     ## covr: skip=2
     .(enter)
+    
+    ## Record the original future strategy set on this worker
+    ...future.strategy.old <- future::plan("list")
+    
     ## Prevent 'future.plan' / R_FUTURE_PLAN settings from being nested
     options(future.plan = NULL)
     Sys.unsetenv("R_FUTURE_PLAN")
+
+    ## Use the next-level-down ("popped") future strategy
     future::plan(.(strategiesR), .cleanup = FALSE, .init = FALSE)
   })
 
@@ -752,7 +758,8 @@ getExpression.Future <- local({
       Sys.unsetenv("R_FUTURE_PLAN")
     else
       Sys.setenv(R_FUTURE_PLAN = .(oenv))
-    future::plan(.(strategies), .cleanup = FALSE, .init = FALSE)
+    ## Revert to the original future strategy
+    future::plan(...future.strategy.old, .cleanup = FALSE, .init = FALSE)
     ## FIXME: If we move .(exit) here, then 'R CMD check' on MS Windows
     ## complain about leftover RscriptXXXXX temporary files. /2022-07-21
     ## .(exit)
@@ -797,9 +804,12 @@ getExpression.Future <- local({
     ## Pass down the default or the remain set of future strategies?
     strategiesR <- strategies[-1]
     ##  mdebugf("Number of remaining strategies: %d", length(strategiesR))
-  
-    ## Identify packages needed by the futures
-    if (length(strategiesR) > 0L) {
+
+    ## Use default future strategy + identify packages needed by the futures
+    if (length(strategiesR) == 0L) {
+      if (debug) mdebug("Packages needed by future strategies (n = 0): <none>")
+      strategiesR <- "default"
+    } else {
       ## Identify package namespaces needed for strategies
       pkgsS <- lapply(strategiesR, FUN = environment)
       pkgsS <- lapply(pkgsS, FUN = environmentName)
@@ -808,8 +818,6 @@ getExpression.Future <- local({
       pkgsS <- intersect(pkgsS, loadedNamespaces())
       if (debug) mdebugf("Packages needed by future strategies (n = %d): %s", length(pkgsS), paste(sQuote(pkgsS), collapse = ", "))
       pkgs <- unique(c(pkgs, pkgsS))
-    } else {
-      if (debug) mdebug("Packages needed by future strategies (n = 0): <none>")
     }
   
     ## Make sure to load and attach all package needed  
@@ -822,10 +830,6 @@ getExpression.Future <- local({
       enter <- bquote_apply(tmpl_enter_packages)
     }
   
-    ## Make sure to set all nested future strategies needed
-    ## Use default future strategy?
-    if (length(strategiesR) == 0L) strategiesR <- "default"
-
     ## Pass down future strategies
     enter <- bquote_apply(tmpl_enter_plan)
     exit <- bquote_apply(tmpl_exit_plan)

From 3cbdb567904aa9e2d8814beb624015783a098681 Mon Sep 17 00:00:00 2001
From: Henrik Bengtsson <henrik.bengtsson@gmail.com>
Date: Fri, 19 Jan 2024 15:08:09 -0800
Subject: [PATCH 2/2] NEWS: Mention performance improvement [ci skip]

---
 NEWS.md | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 16e1e2c9..b56cbe31 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,6 +1,12 @@
 # Version (development version)
 
- * ...
+## Performance
+
+ * Decreased the overhead of launching futures that occurred for future
+   strategies that used a complex `workers` argument. For example,
+   `plan(cluster, workers = cl)`, where `cl` is a `cluster` object,
+   would come with an extra overhead, because the `workers` object was
+   unnecessarily transferred to the cluster nodes.
 
 
 # Version 1.33.1 [2023-12-21]