Now availableCores() falls back to SLURM_CPUS_ON_NODE [#22, #412]

NEWS

@@ -1,7 +1,7 @@
 Package: future
 ===============
 
-Version: 1.18.0-9000 [2020-09-02]
+Version: 1.18.0-9000 [2020-09-18]
 
 SIGNIFICANT CHANGES:
 
@@ -32,6 +32,11 @@ NEW FEATURES:
    the setting on the current system, then an informative FutureWarning is
    produced by such futures.
 
+ * Now availableCores() better supports Slurm.  Specifically, if environment
+   variable 'SLURM_CPUS_PER_TASK' is not set, which requires that option
+   --slurm-cpus-per-task=n' is specified, then it falls back to using
+   'SLURM_CPUS_ON_NODE', which is set when using '--ntasks=n'.
+
 PERFORMANCE:
 
  * Now plan(multisession), plan(cluster, workers = <number>), and

R/availableCores.R

@@ -108,7 +108,38 @@ availableCores <- function(constraints = NULL, methods = getOption("future.avail
     method <- methods[kk]
     if (method == "Slurm") {
       ## Number of cores assigned by Slurm
+
+      ## The assumption is that the following works regardless of
+      ## number of nodes requested /HB 2020-09-18
+      ## Example: --cpus-per-task={n}
       n <- getenv("SLURM_CPUS_PER_TASK")
+      if (is.na(n)) {
+         ## Example: --nodes=1 --ntasks={n} (short: -n {n})
+         ## IMPORTANT: 'SLURM_CPUS_ON_NODE' appears to be rounded up if
+ 	 ## --cpu-per-task is specified, e.g. --nodes=2 --cpus-per-task=3 gives
+	 ## SLURM_CPUS_ON_NODE=4 and SLURM_CPUS_PER_TASK=3. /HB 2020-09-18
+         n <- getenv("SLURM_CPUS_ON_NODE")
+      }
+
+      ## TODO?: Can we validate above assumptions/results? /HB 2020-09-18
+      if (FALSE && !is.na(n)) {
+        ## Is any of the following useful?
+
+        ## Example: --nodes={nnodes} (defaults to 1, short: -N {nnodes})
+        ## From 'man sbatch':
+        ## SLURM_JOB_NUM_NODES (and SLURM_NNODES for backwards compatibility)
+        ## Total number of nodes in the job's resource allocation.
+        nnodes <- getenv("SLURM_JOB_NUM_NODES")
+        if (is.na(nnodes)) nnodes <- getenv("SLURM_NNODES")
+        if (is.na(nnodes)) nnodes <- 1L  ## Can this happen? /HB 2020-09-18
+
+        ## Example: --ntasks={ntasks} (no default, short: -n {ntasks})
+        ## From 'man sbatch':
+        ## SLURM_NTASKS (and SLURM_NPROCS for backwards compatibility)
+        ## Same as -n, --ntasks
+        ntasks <- getenv("SLURM_NTASKS")
+        if (is.na(ntasks)) ntasks <- getenv("SLURM_NPROCS")
+      }
     } else if (method == "PBS") {
       ## Number of cores assigned by TORQUE/PBS
       n <- getenv("PBS_NUM_PPN")

R/availableWorkers.R

@@ -125,6 +125,15 @@ availableWorkers <- function(methods = getOption("future.availableWorkers.method
       if (!identical(nslots, length(w))) {
         warning(sprintf("Identified %d workers from the %s file (%s), which does not match environment variable %s = %d", length(w), sQuote("PE_HOSTFILE"), sQuote(pathname), sQuote("NSLOTS"), nslots))
       }
+    } else if (method == "Slurm") {
+      ## From 'man sbatch':
+      ## SLURM_JOB_NODELIST (and SLURM_NODELIST for backwards compatibility)
+      #  List of nodes allocated to the job.
+      data <- getenv("SLURM_JOB_NODELIST")
+      if (is.na(data)) data <- getenv("SLURM_NODELIST")
+
+      ## TODO: Parse 'data' into a hostnames /HB 2020-09-18
+      ## ...
     } else if (method == "custom") {
       fcn <- getOption("future.availableWorkers.custom", NULL)
       if (!is.function(fcn)) next