Allow backgrounding processes on Mac

base/process/process_mac.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/process/process.h"
+
+#include <mach/mach.h>
+
+#include "base/feature_list.h"
+#include "base/mac/mach_logging.h"
+
+namespace base {
+
+// Enables backgrounding hidden renderers on Mac.
+const Feature kMacAllowBackgroundingProcesses{"MacAllowBackgroundingProcesses",
+                                              FEATURE_DISABLED_BY_DEFAULT};
+
+bool Process::CanBackgroundProcesses() {
+  return FeatureList::IsEnabled(kMacAllowBackgroundingProcesses);
+}
+
+bool Process::IsProcessBackgrounded(PortProvider* port_provider) const {
+  DCHECK(IsValid());
+  if (port_provider == nullptr || !CanBackgroundProcesses())
+    return false;
+
+  mach_port_t task_port = port_provider->TaskForPid(Pid());
+  if (task_port == TASK_NULL)
+    return false;
+
+  task_category_policy_data_t category_policy;
+  mach_msg_type_number_t task_info_count = TASK_CATEGORY_POLICY_COUNT;
+  boolean_t get_default = FALSE;
+
+  kern_return_t result =
+      task_policy_get(task_port, TASK_CATEGORY_POLICY,
+                      reinterpret_cast<task_policy_t>(&category_policy),
+                      &task_info_count, &get_default);
+  MACH_LOG_IF(ERROR, result != KERN_SUCCESS, result)
+      << "task_policy_get TASK_CATEGORY_POLICY";
+
+  if (result == KERN_SUCCESS && get_default == FALSE) {
+    return category_policy.role == TASK_BACKGROUND_APPLICATION;
+  }
+  return false;
+}
+
+bool Process::SetProcessBackgrounded(PortProvider* port_provider,
+                                     bool background) {
+  DCHECK(IsValid());
+  if (port_provider == nullptr || !CanBackgroundProcesses())
+    return false;
+
+  mach_port_t task_port = port_provider->TaskForPid(Pid());
+  if (task_port == TASK_NULL)
+    return false;
+
+  if (IsProcessBackgrounded(port_provider) == background)
+    return true;
+
+  task_category_policy category_policy;
+  category_policy.role =
+      background ? TASK_BACKGROUND_APPLICATION : TASK_FOREGROUND_APPLICATION;
+  kern_return_t result =
+      task_policy_set(task_port, TASK_CATEGORY_POLICY,
+                      reinterpret_cast<task_policy_t>(&category_policy),
+                      TASK_CATEGORY_POLICY_COUNT);
+
+  if (result != KERN_SUCCESS) {
+    MACH_LOG(ERROR, result) << "task_policy_set TASK_CATEGORY_POLICY";
+    return false;
+  }
+
+  // Latency QoS regulates timer throttling/accuracy. Select default tier
+  // on foreground because precise timer firing isn't needed.
+  struct task_qos_policy qos_policy = {
+      background ? LATENCY_QOS_TIER_5 : LATENCY_QOS_TIER_UNSPECIFIED,
+      background ? THROUGHPUT_QOS_TIER_5 : THROUGHPUT_QOS_TIER_UNSPECIFIED};
+  result = task_policy_set(task_port, TASK_OVERRIDE_QOS_POLICY,
+                           reinterpret_cast<task_policy_t>(&qos_policy),
+                           TASK_QOS_POLICY_COUNT);
+  if (result != KERN_SUCCESS) {
+    MACH_LOG(ERROR, result) << "task_policy_set TASK_OVERRIDE_QOS_POLICY";
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace base