deps: improve macOS spawn PATH performance

benchmark/child_process/child-process-spawn-path.js

@@ -0,0 +1,48 @@
+'use strict';
+const common = require('../common.js');
+const { spawnSync } = require('child_process');
+const { basename, delimiter, dirname, join } = require('path');
+const { tmpdir } = require('os');
+
+const bench = common.createBenchmark(main, {
+  n: [100],
+  pathEntries: [0, 8, 32],
+  file: ['path', 'absolute'],
+});
+
+function main({ n, pathEntries, file }) {
+  const originalPath = process.env.PATH;
+  const executable = process.execPath;
+  const executableDir = dirname(executable);
+  const executableName = basename(executable);
+  const missingPaths = [];
+
+  for (let i = 0; i < pathEntries; ++i) {
+    missingPaths.push(join(tmpdir(), `node-spawn-path-missing-${process.pid}-${i}`));
+  }
+
+  process.env.PATH = [...missingPaths, executableDir].join(delimiter);
+
+  const command = file === 'path' ? executableName : executable;
+  const args = ['-e', ''];
+  const options = { stdio: 'ignore' };
+
+  try {
+    const warmup = spawnSync(command, args, options);
+    if (warmup.error)
+      throw warmup.error;
+
+    bench.start();
+    for (let i = 0; i < n; ++i) {
+      const result = spawnSync(command, args, options);
+      if (result.error)
+        throw result.error;
+    }
+    bench.end(n);
+  } finally {
+    if (originalPath === undefined)
+      delete process.env.PATH;
+    else
+      process.env.PATH = originalPath;
+  }
+}

deps/uv/src/unix/process.c

@@ -682,6 +682,7 @@ static int uv__spawn_resolve_and_spawn(const uv_process_options_t* options,
   const char *p;
   const char *z;
   const char *path;
+  const char *parent_path;
   size_t l;
   size_t k;
   int err;
@@ -701,10 +702,7 @@ static int uv__spawn_resolve_and_spawn(const uv_process_options_t* options,
   if (options->env != NULL)
     env = options->env;
 
-  /* If options->file contains a slash, posix_spawn/posix_spawnp should behave
-   * the same, and do not involve PATH resolution at all. The libc
-   * `posix_spawnp` provided by Apple is buggy (since 10.15), so we now emulate it
-   * here, per https://github.com/libuv/libuv/pull/3583. */
+  /* If options->file contains a slash, PATH resolution is not needed. */
   if (strchr(options->file, '/') != NULL) {
     do
       err = posix_spawn(pid, options->file, actions, attrs, options->args, env);
@@ -715,6 +713,21 @@ static int uv__spawn_resolve_and_spawn(const uv_process_options_t* options,
   /* Look for the definition of PATH in the provided env */
   path = uv__spawn_find_path_in_env(env);
 
+  /* Apple's posix_spawnp() resolves PATH from the parent's environment rather
+   * than env. It is safe to use when no cwd change is requested and both PATH
+   * values are identical. This avoids one posix_spawn() call per PATH entry in
+   * the common case. */
+  parent_path = getenv("PATH");
+  if (options->cwd == NULL &&
+      path != NULL &&
+      parent_path != NULL &&
+      strcmp(path, parent_path) == 0) {
+    do
+      err = posix_spawnp(pid, options->file, actions, attrs, options->args, env);
+    while (err == EINTR);
+    return err;
+  }
+
   /* The following resolution logic (execvpe emulation) is copied from
    * https://git.musl-libc.org/cgit/musl/tree/src/process/execvp.c
    * and adapted to work for our specific usage */