Improve nodejs stack size limit heuristic.

nevkontakte · web-flow · commit 877bb505e0b7 · 2022-06-08T20:13:55.000Z
Setting stack size exactly to the system limit will cause node to
segfault before it has a chance to notice that it ran out of space. In
my experiemnts values closer than 64 KiB may still cause a segfault from
time to time.

I also changed the multiplier to 1024, since that's what v8 actually
uses for the flag value.
diff --git a/tool.go b/tool.go
@@ -891,17 +891,23 @@ func runNode(script string, args []string, dir string, quiet bool, out io.Writer
 		// -	OS process limit
 		// -	Node.js (V8) limit
 		//
-		// GopherJS fetches the current OS process limit, and sets the
-		// Node.js limit to the same value. So both limits are kept in sync
-		// and can be controlled by setting OS process limit. E.g.:
+		// GopherJS fetches the current OS process limit, and sets the Node.js limit
+		// to a value slightly below it (otherwise nodejs is likely to segfault).
+		// The backoff size has been determined experimentally on a linux machine,
+		// so it may not be 100% reliable. So both limits are kept in sync and can
+		// be controlled by setting OS process limit. E.g.:
 		//
 		// 	ulimit -s 10000 && gopherjs test
 		//
 		cur, err := sysutil.RlimitStack()
 		if err != nil {
 			return fmt.Errorf("failed to get stack size limit: %v", err)
 		}
-		allArgs = append(allArgs, fmt.Sprintf("--stack_size=%v", cur/1000)) // Convert from bytes to KB.
+		cur = cur / 1024 // Convert bytes to KiB.
+		if backoff := uint64(64); cur > backoff {
+			cur = cur - backoff
+		}
+		allArgs = append(allArgs, fmt.Sprintf("--stack_size=%v", cur))
 	}
 
 	allArgs = append(allArgs, script)
