fix(node): Rework node:child_process IPC (#24763)

Fixes https://github.com/denoland/deno/issues/24756. Fixes
https://github.com/denoland/deno/issues/24796.

This also gets vitest working when using
[`--pool=forks`](https://vitest.dev/guide/improving-performance#pool)
(which is the default as of vitest 2.0). Ref
https://github.com/denoland/deno/issues/23882.

---

This PR resolves a handful of issues with child_process IPC. In
particular:

- We didn't support sending typed array views over IPC
- Opening an IPC channel resulted in the event loop never exiting
- Sending a `null` over IPC would terminate the channel
- There was some UB in the read implementation (transmuting an `&[u8]`
to `&mut [u8]`)
- The `send` method wasn't returning anything, so there was no way to
signal backpressure (this also resulted in the benchmark
`child_process_ipc.mjs` being misleading, as it tried to respect
backpressure. That gave node much worse results at larger message sizes,
and gave us much worse results at smaller message sizes).
- We weren't setting up the `channel` property on the `process` global
(or on the `ChildProcess` object), and also didn't have a way to
ref/unref the channel
- Calling `kill` multiple times (or disconnecting the channel, then
calling kill) would throw an error
- Node couldn't spawn a deno subprocess and communicate with it over IPC

1 files changed, 23 insertions, 2 deletions

diff --git a/ext/node/polyfills/child_process.ts b/ext/node/polyfills/child_process.ts
index 2aba88d63..bb38b746c 100644
--- a/ext/node/polyfills/child_process.ts
+++ b/ext/node/polyfills/child_process.ts
@@ -115,7 +115,8 @@ export function fork(
   // more
   const v8Flags: string[] = [];
   if (Array.isArray(execArgv)) {
-    for (let index = 0; index < execArgv.length; index++) {
+    let index = 0;
+    while (index < execArgv.length) {
       const flag = execArgv[index];
       if (flag.startsWith("--max-old-space-size")) {
         execArgv.splice(index, 1);
@@ -123,6 +124,16 @@ export function fork(
       } else if (flag.startsWith("--enable-source-maps")) {
         // https://github.com/denoland/deno/issues/21750
         execArgv.splice(index, 1);
+      } else if (flag.startsWith("-C") || flag.startsWith("--conditions")) {
+        let rm = 1;
+        if (flag.indexOf("=") === -1) {
+          // --conditions foo
+          // so remove the next argument as well.
+          rm = 2;
+        }
+        execArgv.splice(index, rm);
+      } else {
+        index++;
       }
     }
   }
@@ -825,7 +836,17 @@ export function execFileSync(
 function setupChildProcessIpcChannel() {
   const fd = op_node_child_ipc_pipe();
   if (typeof fd != "number" || fd < 0) return;
-  setupChannel(process, fd);
+  const control = setupChannel(process, fd);
+  process.on("newListener", (name: string) => {
+    if (name === "message" || name === "disconnect") {
+      control.refCounted();
+    }
+  });
+  process.on("removeListener", (name: string) => {
+    if (name === "message" || name === "disconnect") {
+      control.unrefCounted();
+    }
+  });
 }
 
 internals.__setupChildProcessIpcChannel = setupChildProcessIpcChannel;