feat: allow controll of the maximum number of cpus using BELLMAN_NUM_…

…CPUS

src/multicore.rs

@@ -4,6 +4,7 @@
 //! crossbeam but may be extended in the future to
 //! allow for various parallelism strategies.
 
+use std::env;
 use std::any::Any;
 use num_cpus;
 use futures::{Future, IntoFuture, Poll};
@@ -28,7 +29,17 @@ impl Worker {
     }
 
     pub fn new() -> Worker {
-        Self::new_with_cpus(num_cpus::get())
+        let cpus = if let Ok(num) = env::var("BELLMAN_NUM_CPUS") {
+            if let Ok(num) = num.parse() {
+                num
+            } else {
+                num_cpus::get()
+            }
+        } else {
+            num_cpus::get()
+        };
+
+        Self::new_with_cpus(cpus)
     }
 
     pub fn log_num_cpus(&self) -> u32 {