Account for existing but empty cpus file

If a CPU file exists but is empty, previously we reported this file with a CPU count of 1, which resulted in a single-threaded run.

CHANGELOG.md

@@ -6,7 +6,7 @@ Note that the only difference between `v2` and `v3` of the CodeQL Action is the
 
 ## [UNRELEASED]
 
-No user facing changes.
+- Fix an issue where an existing, but empty, `/sys/fs/cgroup/cpuset.cpus` file always resulted in a single-threaded run. [#2151](https://github.com/github/codeql-action/pull/2151)
 
 ## 3.24.3 - 15 Feb 2024
 

lib/util.js

@@ -316,7 +316,10 @@ function getCgroupCpuCountFromCpus(cpusFile, logger) {
     }
     let cpuCount = 0;
     // Comma-separated numbers and ranges, for eg. 0-1,3
-    const cpusString = fs.readFileSync(cpusFile, "utf-8");
+    const cpusString = fs.readFileSync(cpusFile, "utf-8").trim();
+    if (cpusString.length === 0) {
+        return undefined;
+    }
     for (const token of cpusString.split(",")) {
         if (!token.includes("-")) {
             // Not a range

src/util.ts

@@ -453,7 +453,10 @@ function getCgroupCpuCountFromCpus(
 
   let cpuCount = 0;
   // Comma-separated numbers and ranges, for eg. 0-1,3
-  const cpusString = fs.readFileSync(cpusFile, "utf-8");
+  const cpusString = fs.readFileSync(cpusFile, "utf-8").trim();
+  if (cpusString.length === 0) {
+    return undefined;
+  }
   for (const token of cpusString.split(",")) {
     if (!token.includes("-")) {
       // Not a range