From e92a05b5518e5fd30559c96c5990b08657bbc3e4 Mon Sep 17 00:00:00 2001
From: Nathan Whitaker <17734409+nathanwhit@users.noreply.github.com>
Date: Wed, 14 Aug 2024 15:26:21 -0700
Subject: feat(serve): Opt-in parallelism for `deno serve` (#24920)
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Adds a `parallel` flag to `deno serve`. When present, we spawn multiple
workers to parallelize serving requests.


```bash
deno serve --parallel main.ts
```

Currently on linux we use `SO_REUSEPORT` and rely on the fact that the
kernel will distribute connections in a round-robin manner.

On mac and windows, we sort of emulate this by cloning the underlying
file descriptor and passing a handle to each worker. The connections
will not be guaranteed to be fairly distributed (and in practice almost
certainly won't be), but the distribution is still spread enough to
provide a significant performance increase.

---
(Run on an Macbook Pro with an M3 Max, serving `deno.com`

baseline::
```
❯ wrk -d 30s -c 125 --latency http://127.0.0.1:8000
Running 30s test @ http://127.0.0.1:8000
  2 threads and 125 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   239.78ms   13.56ms 330.54ms   79.12%
    Req/Sec   258.58     35.56   360.00     70.64%
  Latency Distribution
     50%  236.72ms
     75%  248.46ms
     90%  256.84ms
     99%  268.23ms
  15458 requests in 30.02s, 2.47GB read
Requests/sec:    514.89
Transfer/sec:     84.33MB
```

this PR (`with --parallel` flag)
```
❯ wrk -d 30s -c 125 --latency http://127.0.0.1:8000
Running 30s test @ http://127.0.0.1:8000
  2 threads and 125 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency   117.40ms  142.84ms 590.45ms   79.07%
    Req/Sec     1.33k   175.19     1.77k    69.00%
  Latency Distribution
     50%   22.34ms
     75%  223.67ms
     90%  357.32ms
     99%  460.50ms
  79636 requests in 30.07s, 12.74GB read
Requests/sec:   2647.96
Transfer/sec:    433.71MB
```
---
 runtime/js/99_main.js | 49 +++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 41 insertions(+), 8 deletions(-)

(limited to 'runtime/js')

diff --git a/runtime/js/99_main.js b/runtime/js/99_main.js
index ca96e34b7..5e25a3818 100644
--- a/runtime/js/99_main.js
+++ b/runtime/js/99_main.js
@@ -45,6 +45,7 @@ const {
   PromiseResolve,
   SafeSet,
   StringPrototypeIncludes,
+  StringPrototypePadEnd,
   StringPrototypeSplit,
   StringPrototypeTrim,
   Symbol,
@@ -709,8 +710,37 @@ function bootstrapMainRuntime(runtimeOptions, warmup = false) {
       11: mode,
       12: servePort,
       13: serveHost,
+      14: serveIsMain,
+      15: serveWorkerCount,
     } = runtimeOptions;
 
+    if (mode === executionModes.serve) {
+      if (serveIsMain && serveWorkerCount) {
+        const origLog = console.log;
+        const origError = console.error;
+        const prefix = `[serve-worker-0 ]`;
+        console.log = (...args) => {
+          return origLog(prefix, ...new primordials.SafeArrayIterator(args));
+        };
+        console.error = (...args) => {
+          return origError(prefix, ...new primordials.SafeArrayIterator(args));
+        };
+      } else if (serveWorkerCount !== null) {
+        const origLog = console.log;
+        const origError = console.error;
+        const base = `serve-worker-${serveWorkerCount + 1}`;
+        // 15 = "serve-worker-nn".length, assuming
+        // serveWorkerCount < 100
+        const prefix = `[${StringPrototypePadEnd(base, 15, " ")}]`;
+        console.log = (...args) => {
+          return origLog(prefix, ...new primordials.SafeArrayIterator(args));
+        };
+        console.error = (...args) => {
+          return origError(prefix, ...new primordials.SafeArrayIterator(args));
+        };
+      }
+    }
+
     if (mode === executionModes.run || mode === executionModes.serve) {
       let serve = undefined;
       core.addMainModuleHandler((main) => {
@@ -725,13 +755,16 @@ function bootstrapMainRuntime(runtimeOptions, warmup = false) {
         }
 
         if (mode === executionModes.serve && !serve) {
-          console.error(
-            `%cerror: %cdeno serve requires %cexport default { fetch }%c in the main module, did you mean to run \"deno run\"?`,
-            "color: yellow;",
-            "color: inherit;",
-            "font-weight: bold;",
-            "font-weight: normal;",
-          );
+          if (serveIsMain) {
+            // Only error if main worker
+            console.error(
+              `%cerror: %cdeno serve requires %cexport default { fetch }%c in the main module, did you mean to run \"deno run\"?`,
+              "color: yellow;",
+              "color: inherit;",
+              "font-weight: bold;",
+              "font-weight: normal;",
+            );
+          }
           return;
         }
 
@@ -746,7 +779,7 @@ function bootstrapMainRuntime(runtimeOptions, warmup = false) {
             );
           }
           if (mode === executionModes.serve) {
-            serve({ servePort, serveHost });
+            serve({ servePort, serveHost, serveIsMain, serveWorkerCount });
           }
         }
       });
-- 
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