[build] Limit the number of concurrent dart/gen_snapshot actions.

Ninja may be run with a large --jobs value to run more C/C++ compilation actions in parallel on remote workers. The dart and gen_snapshot actions during the build should in this case remain limited to the number of cores on the machine to avoid a coincident memory usage that is too high.

When running in the Dart tree with RBE, limit this by changing the RBE exec_strategy away from racing. Otherwise, use a pool to limit the concurrency of this action type.

TEST=build.py --no-rbe -j1000
Bug: flutter/flutter#164591
Change-Id: Ia5e5615d0067b34d49871f26ead074cb891baf70
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/423562
Reviewed-by: Alexander Aprelev <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

build/dart/BUILD.gn

@@ -0,0 +1,9 @@
+# Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+if (current_toolchain == default_toolchain) {
+  pool("dart_action_pool") {
+    depth = exec_script("num_cpus.py", [], "value")
+  }
+}

build/dart/dart_action.gni

@@ -98,6 +98,8 @@ template("_compiled_action") {
                 "--exec_strategy=" + rbe_expensive_exec_strategy,
                 "--",
               ]
+    } else if (!defined(invoker.pool)) {
+      pool = "$_dart_root/build/dart:dart_action_pool($default_toolchain)"
     }
 
     args += [ rebase_path(host_executable, root_build_dir) ] + invoker.args
@@ -148,6 +150,8 @@ template("_prebuilt_tool_action") {
                 "--exec_strategy=" + rbe_expensive_exec_strategy,
                 "--",
               ]
+    } else if (!defined(invoker.pool)) {
+      pool = "$_dart_root/build/dart:dart_action_pool($default_toolchain)"
     }
 
     args += [ rebase_path(invoker.binary, root_build_dir) ] + vm_args

build/dart/num_cpus.py

@@ -0,0 +1,8 @@
+#!/usr/bin/env python3
+# Copyright 2025 The Dart Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import multiprocessing
+
+print(multiprocessing.cpu_count())

build/toolchain/rbe.gni

@@ -19,8 +19,10 @@ declare_args() {
   # Set to the docker image to use in the RBE.
   rbe_image = "docker://gcr.io/cloud-marketplace/google/debian11@sha256:69e2789c9f3d28c6a0f13b25062c240ee7772be1f5e6d41bb4680b63eae6b304"
 
-  # Do expensive RBE compilations both locally and remotely, whatever is faster.
-  rbe_expensive_exec_strategy = "racing"
+  # Do expensive RBE actions remotely, falling back to local on failure/timeout.
+  # The "racing" strategy can cause a memory exhaustion problem if too many
+  # actions run locally at the same time.
+  rbe_expensive_exec_strategy = "remote_local_fallback"
 
   rbe_exec_root = rebase_path("//", root_build_dir)
 

runtime/vm/os_thread_linux.cc

@@ -9,7 +9,6 @@
 #include "vm/os_thread.h"
 
 #include <errno.h>
-#include <fcntl.h>
 #include <stdio.h>
 #include <sys/resource.h>
 #include <sys/syscall.h>
@@ -115,39 +114,6 @@ int OSThread::TryStart(const char* name,
 
   pthread_t tid;
   result = pthread_create(&tid, &attr, ThreadStart, data);
-  if (result != 0) {
-    fprintf(stderr, "pthread_create failed\n");
-    const char* const kPaths[] = {
-        "/proc/self/limits",
-        "/proc/sys/kernel/threads-max",
-        "/proc/sys/kernel/pid_max",
-        "/sys/fs/cgroup/user.slice/memory.current",
-        "/sys/fs/cgroup/user.slice/memory.max",
-        "/sys/fs/cgroup/user.slice/memory.peak",
-        "/sys/fs/cgroup/user.slice/pids.current",
-        "/sys/fs/cgroup/user.slice/pids.max",
-        "/sys/fs/cgroup/user.slice/pids.peak",
-    };
-    for (uintptr_t i = 0; i < ARRAY_SIZE(kPaths); i++) {
-      const char* path = kPaths[i];
-
-      int fd = open(path, O_RDONLY | O_CLOEXEC);
-      if (fd < 0) {
-        fprintf(stderr, "%s: Failed to open\n", path);
-        continue;
-      }
-      const intptr_t kBufferSize = 2048;
-      char buffer[kBufferSize];
-      memset(buffer, 0, kBufferSize);
-      ssize_t red = read(fd, buffer, kBufferSize - 1);
-      close(fd);
-      if (red < 0) {
-        fprintf(stderr, "%s: Failed to read\n", path);
-        continue;
-      }
-      fprintf(stderr, "%s: %s\n", path, buffer);
-    }
-  }
   RETURN_ON_PTHREAD_FAILURE(result);
 
   result = pthread_attr_destroy(&attr);