Fixes #9404

packages/bun-types/bun.d.ts

@@ -4195,19 +4195,19 @@ declare module "bun" {
     };
 
     /**
-     * The amount of CPU time used by the process, in nanoseconds.
+     * The amount of CPU time used by the process, in microseconds.
      */
     cpuTime: {
       /**
-       * User CPU time used by the process, in nanoseconds.
+       * User CPU time used by the process, in microseconds.
        */
       user: number;
       /**
-       * System CPU time used by the process, in nanoseconds.
+       * System CPU time used by the process, in microseconds.
        */
       system: number;
       /**
-       * Total CPU time used by the process, in nanoseconds.
+       * Total CPU time used by the process, in microseconds.
        */
       total: number;
     };

src/bun.js/api/bun/process.zig

@@ -849,9 +849,13 @@ const WaiterThreadPosix = struct {
 
                 _ = std.os.poll(&polls, std.math.maxInt(i32)) catch 0;
 
-                // Make sure we consume any pending signals
+                // Make sure we consume any pending:
+                // - signals
+                // - eventfd
+                // See https://github.com/oven-sh/bun/issues/9404
                 var buf: [1024]u8 = undefined;
-                _ = std.os.read(this.signalfd.cast(), &buf) catch 0;
+                while (bun.sys.read(this.signalfd.cast(), &buf).unwrap() catch 0 > 0) {}
+                while (bun.sys.read(this.eventfd.cast(), &buf).unwrap() catch 0 > 0) {}
             } else {
                 var mask = std.os.empty_sigset;
                 var signal: c_int = std.os.SIG.CHLD;

test/js/bun/spawn/spawn_waiter_thread-fixture.js

@@ -0,0 +1,7 @@
+const { spawn } = require("child_process");
+
+if (!process.env.BUN_GARBAGE_COLLECTOR_LEVEL || !process.env.BUN_FEATURE_FLAG_FORCE_WAITER_THREAD) {
+  throw new Error("This test must be run with BUN_GARBAGE_COLLECTOR_LEVEL and BUN_FEATURE_FLAG_FORCE_WAITER_THREAD");
+}
+
+spawn("sleep", ["infinity"]).ref();

test/js/bun/spawn/spawn_waiter_thread.test.ts

@@ -0,0 +1,27 @@
+import { test, expect } from "bun:test";
+import { spawn } from "bun";
+import { bunEnv, bunExe } from "harness";
+import { join } from "path";
+
+if (process.platform === "linux") {
+  test("issue #9404", async () => {
+    const proc = spawn({
+      env: {
+        ...bunEnv,
+        BUN_GARBAGE_COLLECTOR_LEVEL: "1",
+        BUN_FEATURE_FLAG_FORCE_WAITER_THREAD: "1",
+      },
+      stderr: "inherit",
+      cmd: [bunExe(), join(__dirname, "spawn_waiter_thread-fixture.js")],
+    });
+
+    setTimeout(() => {
+      proc.kill();
+    }, 1000);
+
+    await proc.exited;
+
+    const resourceUsage = proc.resourceUsage();
+    expect(resourceUsage?.cpuTime.total).toBeLessThan(750_000n);
+  });
+}