log tbb header and library provenance during install

NEWS.md

@@ -1,5 +1,11 @@
 # RcppParallel (development version)
 
+* RcppParallel now reports which TBB headers and libraries are installed
+  with the package, and from where, during package installation. In
+  addition, setting the `VERBOSE` environment variable to a value other
+  than `0` enables diagnostics describing how TBB libraries are resolved
+  and loaded when the package is loaded.
+
 * On Windows, RcppParallel once again loads its compatibility stub library
   (`tbb.dll`) when the package is loaded. Packages linking with `-ltbb`
   (e.g. via StanHeaders) record a load-time dependency on `tbb.dll`, which

R/utils.R

@@ -1,4 +1,13 @@
 
+# opt-in diagnostics, primarily useful when debugging issues with
+# TBB library resolution and loading during package load; uses the
+# same VERBOSE environment variable as the TBB build in install.libs.R
+verboseMessage <- function(fmt, ...) {
+   verbose <- Sys.getenv("VERBOSE", unset = "0")
+   if (!identical(verbose, "0"))
+      message(sprintf(fmt, ...))
+}
+
 # like system.file(), but injects the architecture-specific subdirectory
 # used on Windows when set; e.g. archSystemFile("lib") resolves 'lib/x64'
 archSystemFile <- function(dir, name = NULL) {

R/zzz.R

@@ -24,22 +24,28 @@ loadTbbLibrary <- function(name) {
       # install.libs.R places the stub; tbbRoot() would prefer TBB_LIB,
       # which on Windows points at Rtools and holds only static libraries
       path <- archSystemFile("lib", paste0(name, ".dll"))
-      if (!file.exists(path))
+      if (!file.exists(path)) {
+         verboseMessage("TBB library '%s' not found in package 'lib' folder; skipping", name)
          return(NULL)
+      }
 
+      verboseMessage("loading TBB library '%s'", path)
       return(dyn.load(path, local = FALSE, now = TRUE))
 
    }
 
    path <- tbbLibraryPath(name)
-   if (is.null(path))
+   if (is.null(path)) {
+      verboseMessage("TBB library '%s' could not be resolved; skipping", name)
       return(NULL)
-
+   }
+
    if (!file.exists(path)) {
       warning("TBB library ", shQuote(name), " not found.")
       return(NULL)
    }
-
+
+   verboseMessage("loading TBB library '%s'", path)
    dyn.load(path, local = FALSE, now = TRUE)
 
 }

src/install.libs.R

@@ -38,12 +38,14 @@
    if (!nzchar(tbbLib)) {
 
       # using bundled TBB
+      tbbSrc <- "tbb/build/lib_release"
       tbbLibs <- list.files(
-         path       = "tbb/build/lib_release",
+         path       = tbbSrc,
          pattern    = shlibPattern,
          full.names = TRUE
       )
 
+      logTbbLibraries(tbbLibs, tbbSrc)
       for (tbbLib in tbbLibs) {
          system2("cp", c("-P", shQuote(tbbLib), shQuote(tbbDest)))
       }
@@ -61,6 +63,7 @@
       tbbLibs <- tbbLibs[!nzchar(Sys.readlink(tbbLibs))]
 
       # copy / link the libraries
+      logTbbLibraries(tbbLibs, tbbLib)
       useSymlinks <- Sys.getenv("TBB_USE_SYMLINKS", unset = .Platform$OS.type != "windows")
       if (useSymlinks) {
          file.symlink(tbbLibs, tbbDest)
@@ -76,7 +79,9 @@
    # older binaries (like rstan) can still load
    if (.Platform$OS.type == "windows") {
       tbbDll <- file.path(tbbDest, "tbb.dll")
-      if (!file.exists(tbbDll)) {
+      if (file.exists(tbbDll)) {
+         writeLines("** tbb.dll already exists; skipping tbb stub library")
+      } else {
          writeLines("** creating tbb stub library")
          status <- system("R CMD SHLIB -o tbb-compat/tbb.dll tbb-compat/tbb-compat.cpp")
          if (status != 0)
@@ -87,8 +92,22 @@
 
 }
 
+# Report which TBB libraries are about to be installed, and from where.
+# Stale or unexpected libraries copied here have historically been a
+# subtle source of load failures in downstream packages, so make the
+# provenance easy to spot in installation logs.
+logTbbLibraries <- function(tbbLibs, source) {
+   if (length(tbbLibs)) {
+      fmt <- "** copying TBB libraries from '%s' [%s]"
+      writeLines(sprintf(fmt, source, paste(basename(tbbLibs), collapse = ", ")))
+   } else {
+      writeLines(sprintf("** no TBB libraries found in '%s'", source))
+   }
+}
+
 useTbbPreamble <- function(tbbInc) {
 
+   writeLines(sprintf("** copying TBB headers from '%s'", tbbInc))
    dir.create("../inst/include", recursive = TRUE, showWarnings = FALSE)
    for (suffix in c("oneapi", "serial", "tbb")) {
       tbbPath <- file.path(tbbInc, suffix)