Add support for backgrounding processes on the Mac

base/process/process_mac.cc

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.

[Robert Sesek, 2015/03/10 18:27:43]

nit: no (c)

[shrike, 2015/03/11 21:38:21]

Done (but FYI I just copy/pasted from process_linux.cc and changed the date).

[Robert Sesek, 2015/03/12 16:00:23]

Yup, the copyright policy changed over time.

+// 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"

[Robert Sesek, 2015/03/10 18:27:43]

nit: blank line after

[shrike, 2015/03/11 21:38:21]

I added the blank line (what is the rule)?

[Robert Sesek, 2015/03/12 16:00:23]

http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Names_and_Ord...

[shrike, 2015/03/18 16:20:22]

Thank you.

+#include "base/mac/mac_util.h"
+#include <mach/mach.h>
+
+// The following was added to <mach/task_policy.h> after 10.8

[Robert Sesek, 2015/03/10 18:27:43]

nit: punctuation

[shrike, 2015/03/11 21:38:21]

Done.

+#ifndef TASK_OVERRIDE_QOS_POLICY
+
+#define TASK_OVERRIDE_QOS_POLICY 9
+
+typedef struct task_category_policy task_category_policy_data_t;
+typedef struct task_category_policy* task_category_policy_t;
+
+enum task_latency_qos {
+  LATENCY_QOS_TIER_UNSPECIFIED = 0x0,
+  LATENCY_QOS_TIER_0 = ((0xFF << 16) | 1),
+  LATENCY_QOS_TIER_1 = ((0xFF << 16) | 2),
+  LATENCY_QOS_TIER_2 = ((0xFF << 16) | 3),
+  LATENCY_QOS_TIER_3 = ((0xFF << 16) | 4),
+  LATENCY_QOS_TIER_4 = ((0xFF << 16) | 5),
+  LATENCY_QOS_TIER_5 = ((0xFF << 16) | 6)
+};
+typedef integer_t task_latency_qos_t;
+enum task_throughput_qos {
+  THROUGHPUT_QOS_TIER_UNSPECIFIED = 0x0,
+  THROUGHPUT_QOS_TIER_0 = ((0xFE << 16) | 1),
+  THROUGHPUT_QOS_TIER_1 = ((0xFE << 16) | 2),
+  THROUGHPUT_QOS_TIER_2 = ((0xFE << 16) | 3),
+  THROUGHPUT_QOS_TIER_3 = ((0xFE << 16) | 4),
+  THROUGHPUT_QOS_TIER_4 = ((0xFE << 16) | 5),
+  THROUGHPUT_QOS_TIER_5 = ((0xFE << 16) | 6),
+};
+
+#define LATENCY_QOS_LAUNCH_DEFAULT_TIER LATENCY_QOS_TIER_3
+#define THROUGHPUT_QOS_LAUNCH_DEFAULT_TIER THROUGHPUT_QOS_TIER_3
+
+typedef integer_t task_throughput_qos_t;
+
+struct task_qos_policy {
+  task_latency_qos_t task_latency_qos_tier;
+  task_throughput_qos_t task_throughput_qos_tier;
+};
+
+typedef struct task_qos_policy* task_qos_policy_t;
+#define TASK_QOS_POLICY_COUNT \
+  ((mach_msg_type_number_t)(sizeof(struct task_qos_policy) / sizeof(integer_t)))
+
+#endif  // TASK_OVERRIDE_QOS_POLICY
+
+namespace base {
+
+bool Process::CanBackgroundProcesses() {
+  return true;

[Robert Sesek, 2015/03/10 18:27:43]

This isn't true unconditionally. This should probably return
mac::IsOSMountainLionOrLater(), right?

[shrike, 2015/03/11 21:38:21]

You can foreground/background a task on prior versions of the OS, it's just the
quality of service settings that are only as of Mavericks. I have a check in
SetProcessBackgrounded() to bail before the QoS code if you're running <
Mavericks.

[Robert Sesek, 2015/03/12 16:00:23]

Ah, my mistake. I missed that in the 10.6 kernel.

+}
+
+bool Process::IsProcessBackgrounded(mach_port_t process_port) const {
+  // See SetProcessBackgrounded().
+  DCHECK(IsValid());
+
+  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(process_port, TASK_CATEGORY_POLICY,
+                                         (task_policy_t)&category_policy,

[Robert Sesek, 2015/03/10 18:27:43]

C-style casts are banned by Google style guide. Use reinterpret_cast<>.

[shrike, 2015/03/11 21:38:21]

Done.

+                                         &task_info_count, &get_default);
+  DPCHECK(result == KERN_SUCCESS);

[Robert Sesek, 2015/03/10 18:27:43]

This will fail on older kernels. PCHECK is also not the right one to use, since
this won't set errno, but rather the kern_return_t will be set. We have
base/mac/mach_logging.h to help here.

[shrike, 2015/03/11 21:38:21]

Looks like I borrowed some code from process_linux.cc instead of
process_posix.cc. I have changed them to DCHECKs.

[Robert Sesek, 2015/03/12 16:00:23]

I suggested you look at mach_logging.h because we have MACH_DCHECK:

https://code.google.com/p/chromium/codesearch#chromium/src/base/mac/mach_logg...

[shrike, 2015/03/18 16:20:22]

Thank you. I haven't done a lot of kernel work so I wasn't sure what to be on
the lookout for. Done.

+
+  if (result == KERN_SUCCESS && get_default == FALSE) {
+    return category_policy.role == TASK_BACKGROUND_APPLICATION;
+  }
+  return false;
+}
+
+bool Process::SetProcessBackgrounded(mach_port_t process_port,
+                                     bool background) {
+  DCHECK(IsValid());
+
+  if (!CanBackgroundProcesses() || process_port == 0) {

[Robert Sesek, 2015/03/10 18:27:43]

TASK_NULL instead of 0.

[shrike, 2015/03/11 21:38:21]

Done. I know that TASK_NULL is 0 but I had a reason for saying 0 instead (not
sure it's worth the typing to explain).

+    return false;
+  }
+
+  struct task_category_policy taskCatPolicy;

[Robert Sesek, 2015/03/10 18:27:43]

Naming: use under_score variable names and spell out the full words like you do
in IsProcessBackgrounded.

[shrike, 2015/03/11 21:38:21]

Done.

+  taskCatPolicy.role =
+      background ? TASK_BACKGROUND_APPLICATION : TASK_FOREGROUND_APPLICATION;
+  kern_return_t result = task_policy_set(process_port, TASK_CATEGORY_POLICY,
+                                         (thread_policy_t)&taskCatPolicy,
+                                         TASK_CATEGORY_POLICY_COUNT);
+  DPCHECK(result == KERN_SUCCESS);
+
+  if (result != KERN_SUCCESS) {
+    return false;
+  } else if (!mac::IsOSMavericksOrLater()) {
+    return true;
+  }
+
+  // Latency QoS regulates timer throttling/accuracy. Select default tier
+  // on foreground because precise timer firing isn't needed
+  struct task_qos_policy qosinfo = {
+      background ? LATENCY_QOS_TIER_5 : LATENCY_QOS_LAUNCH_DEFAULT_TIER,
+      background ? THROUGHPUT_QOS_TIER_5 : THROUGHPUT_QOS_LAUNCH_DEFAULT_TIER};
+  result = task_policy_set(process_port, TASK_OVERRIDE_QOS_POLICY,
+                           (task_policy_t)&qosinfo, TASK_QOS_POLICY_COUNT);
+  DPCHECK(result == KERN_SUCCESS);
+
+  return result == KERN_SUCCESS;
+}
+
+}  // namespace base