From 79b6e6f1af684809ad1ee9c5a62e564f1648c8d1 Mon Sep 17 00:00:00 2001
From: "trop[bot]" <trop[bot]@users.noreply.github.com>
Date: Sat, 15 Dec 2018 14:14:59 -0800
Subject: [PATCH] fix: allow 2 threads for CreateIoCompletionPort on
 single-core to prevent busy looping (backport: 3-0-x) (#16082)

---
 atom/common/node_bindings_win.cc | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/atom/common/node_bindings_win.cc b/atom/common/node_bindings_win.cc
index 4a5ff5c51406..0f592a3f5f68 100644
--- a/atom/common/node_bindings_win.cc
+++ b/atom/common/node_bindings_win.cc
@@ -7,6 +7,7 @@
 #include <windows.h>
 
 #include "base/logging.h"
+#include "base/sys_info.h"
 
 extern "C" {
 #include "vendor/node/deps/uv/src/win/internal.h"
@@ -15,7 +16,20 @@ extern "C" {
 namespace atom {
 
 NodeBindingsWin::NodeBindingsWin(BrowserEnvironment browser_env)
-    : NodeBindings(browser_env) {}
+    : NodeBindings(browser_env) {
+  // on single-core the io comp port NumberOfConcurrentThreads needs to be 2
+  // to avoid cpu pegging likely caused by a busy loop in PollEvents
+  if (base::SysInfo::NumberOfProcessors() == 1) {
+    // the expectation is the uv_loop_ has just been initialized
+    // which makes iocp replacement safe
+    CHECK_EQ(0u, uv_loop_->active_handles);
+    CHECK_EQ(0u, uv_loop_->active_reqs.count);
+
+    if (uv_loop_->iocp && uv_loop_->iocp != INVALID_HANDLE_VALUE)
+      CloseHandle(uv_loop_->iocp);
+    uv_loop_->iocp = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 2);
+  }
+}
 
 NodeBindingsWin::~NodeBindingsWin() {}