fix(child_process) unref next tick so exit/close event can be fired before application exits (#5481)

* unref next tick so exit callback can be called

* fmt + test

* oops

* add ref_count

* update pending

* comment and fix

src/bun.js/api/bun/subprocess.zig

@@ -68,6 +68,7 @@ pub const Subprocess = struct {
     ipc_callback: JSC.Strong = .{},
     ipc_buffer: bun.ByteList,
 
+    has_pending_unref: bool = false,
     pub const SignalCode = bun.SignalCode;
 
     pub const IPCMode = enum {
@@ -82,7 +83,7 @@ pub const Subprocess = struct {
 
     pub fn updateHasPendingActivityFlag(this: *Subprocess) void {
         @fence(.SeqCst);
-        this.has_pending_activity.store(this.waitpid_err == null and this.exit_code == null and this.ipc == .none, .SeqCst);
+        this.has_pending_activity.store(this.waitpid_err == null and this.exit_code == null and this.ipc == .none and this.has_pending_unref, .SeqCst);
     }
 
     pub fn hasPendingActivity(this: *Subprocess) callconv(.C) bool {
@@ -92,7 +93,7 @@ pub const Subprocess = struct {
 
     pub fn updateHasPendingActivity(this: *Subprocess) void {
         @fence(.Release);
-        this.has_pending_activity.store(this.waitpid_err == null and this.exit_code == null and this.ipc == .none, .Release);
+        this.has_pending_activity.store(this.waitpid_err == null and this.exit_code == null and this.ipc == .none and this.has_pending_unref, .Release);
     }
 
     pub fn ref(this: *Subprocess) void {
@@ -111,8 +112,10 @@ pub const Subprocess = struct {
         }
     }
 
+    /// This disables the keeping process alive flag on the poll and also in the stdin, stdout, and stderr
     pub fn unref(this: *Subprocess) void {
         var vm = this.globalThis.bunVM();
+
         if (this.poll_ref) |poll| poll.disableKeepingProcessAlive(vm);
         if (!this.hasCalledGetter(.stdin)) {
             this.stdin.unref();
@@ -1805,8 +1808,29 @@ pub const Subprocess = struct {
             }
         }
 
-        if (this.hasExited())
-            this.unref();
+        if (this.hasExited()) {
+            const Holder = struct {
+                process: *Subprocess,
+                task: JSC.AnyTask,
+
+                pub fn unref(self: *@This()) void {
+                    // this calls disableKeepingProcessAlive on pool_ref and stdin, stdout, stderr
+                    self.process.unref();
+                    self.process.has_pending_unref = false;
+                    self.process.updateHasPendingActivity();
+                    bun.default_allocator.destroy(self);
+                }
+            };
+
+            var holder = bun.default_allocator.create(Holder) catch @panic("OOM");
+            this.has_pending_unref = true;
+            holder.* = .{
+                .process = this,
+                .task = JSC.AnyTask.New(Holder, Holder.unref).init(holder),
+            };
+
+            this.globalThis.bunVM().enqueueTask(JSC.Task.init(&holder.task));
+        }
     }
 
     const os = std.os;

test/js/node/child_process/child_process.test.ts

@@ -2,6 +2,8 @@ import { describe, it, expect } from "bun:test";
 import { ChildProcess, spawn, execFile, exec, fork, spawnSync, execFileSync, execSync } from "node:child_process";
 import { tmpdir } from "node:os";
 import { promisify } from "node:util";
+import { bunExe, bunEnv } from "harness";
+import path from "path";
 
 const debug = process.env.DEBUG ? console.log : () => {};
 
@@ -308,3 +310,23 @@ describe("Bun.spawn()", () => {
   //   expect(child.pid).toBe(undefined);
   // });
 });
+
+it("should call close and exit before process exits", async () => {
+  const proc = Bun.spawn({
+    cmd: [bunExe(), path.join("fixtures", "child-process-exit-event.js")],
+    cwd: import.meta.dir,
+    env: bunEnv,
+    stdout: "pipe",
+  });
+  await proc.exited;
+  expect(proc.exitCode).toBe(0);
+  let data = "";
+  const reader = proc.stdout.getReader();
+  while (true) {
+    const { done, value } = await reader.read();
+    if (done) break;
+    data += new TextDecoder().decode(value);
+  }
+  expect(data).toContain("closeHandler called");
+  expect(data).toContain("exithHandler called");
+});

test/js/node/child_process/fixtures/child-process-exit-event.js

@@ -0,0 +1,13 @@
+const { spawn } = require("node:child_process");
+
+function exitHandler() {
+  console.log("exithHandler called");
+}
+function closeHandler() {
+  console.log("closeHandler called");
+}
+
+const p = spawn("bun", ["--version"]);
+
+p.on("exit", exitHandler);
+p.on("close", closeHandler);