dgram: use `uv_udp_try_send()`

This improves dgram performance by avoiding unnecessary async
operations.

One issue with this commit is that it seems hard to actually create
conditions under which the fallback path to the async case is
actually taken, for all supported OS, so an internal CLI option
is used for testing that path.

Another caveat is that the lack of an async operation means
that there are slight timing differences (essentially `nextTick()`
rather than `setImmediate()` for the send callback).

PR-URL: https://github.com/nodejs/node/pull/29832
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

3 files changed, 3 insertions, 2 deletions

diff --git a/test/async-hooks/test-udpsendwrap.js b/test/async-hooks/test-udpsendwrap.js
index 25b7eb6103..f1403e3226 100644
--- a/test/async-hooks/test-udpsendwrap.js
+++ b/test/async-hooks/test-udpsendwrap.js
@@ -1,3 +1,4 @@
+// Flags: --test-udp-no-try-send
 'use strict';
 
 const common = require('../common');
diff --git a/test/parallel/test-dgram-send-callback-recursive.js b/test/parallel/test-dgram-send-callback-recursive.js
index 835fa332df..1a4c7c84fc 100644
--- a/test/parallel/test-dgram-send-callback-recursive.js
+++ b/test/parallel/test-dgram-send-callback-recursive.js
@@ -22,7 +22,7 @@ function onsend() {
 client.on('listening', function() {
   port = this.address().port;
 
-  setImmediate(function() {
+  process.nextTick(() => {
     async = true;
   });
 
diff --git a/test/sequential/test-async-wrap-getasyncid.js b/test/sequential/test-async-wrap-getasyncid.js
index f2702b4b49..bef6b050ff 100644
--- a/test/sequential/test-async-wrap-getasyncid.js
+++ b/test/sequential/test-async-wrap-getasyncid.js
@@ -1,5 +1,5 @@
 'use strict';
-// Flags: --expose-gc --expose-internals --no-warnings
+// Flags: --expose-gc --expose-internals --no-warnings --test-udp-no-try-send
 
 const common = require('../common');
 const { internalBinding } = require('internal/test/binding');