chrome/browser/chromeos/arc/process/arc_process_service.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.
//
// The main point of this class is to cache ARC proc nspid<->pid mapping
// globally. Since the calculation is costly, a dedicated worker thread is
// used. All read/write of its internal data structure (i.e., the mapping)
// should be on this thread.

#include "chrome/browser/chromeos/arc/process/arc_process_service.h"

#include <algorithm>
#include <queue>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>

#include "base/callback.h"
#include "base/logging.h"
#include "base/process/process.h"
#include "base/process/process_iterator.h"
#include "base/task_runner_util.h"
#include "base/trace_event/trace_event.h"
#include "components/arc/arc_bridge_service.h"
#include "content/public/browser/browser_thread.h"

namespace arc {

using base::kNullProcessId;
using base::Process;
using base::ProcessId;
using std::vector;

namespace {

// Weak pointer.  This class is owned by ArcServiceManager.
ArcProcessService* g_arc_process_service = nullptr;
static constexpr char kInitName[] = "/init";
static constexpr bool kNotFocused = false;
static constexpr int64_t kNoActivityTimeInfo = 0L;

// Matches the process name "/init" in the process tree and get the
// corresponding process ID.
base::ProcessId GetArcInitProcessId(
    const base::ProcessIterator::ProcessEntries& entry_list) {
  for (const base::ProcessEntry& entry : entry_list) {
    if (entry.cmd_line_args().empty()) {
      continue;
    }
    // TODO(nya): Add more constraints to avoid mismatches.
    const std::string& process_name = entry.cmd_line_args()[0];
    if (process_name == kInitName) {
      return entry.pid();
    }
  }
  return base::kNullProcessId;
}

std::vector<ArcProcess> GetArcSystemProcessList() {
  std::vector<ArcProcess> ret_processes;
  const base::ProcessIterator::ProcessEntries& entry_list =
      base::ProcessIterator(nullptr).Snapshot();
  const base::ProcessId arc_init_pid = GetArcInitProcessId(entry_list);

  if (arc_init_pid == base::kNullProcessId) {
    return ret_processes;
  }

  // Enumerate the child processes of ARC init for gathering ARC System
  // Processes.
  for (const base::ProcessEntry& entry : entry_list) {
    if (entry.cmd_line_args().empty()) {
      continue;
    }
    // TODO(hctsai): For now, we only gather direct child process of init, need
    // to get the processes below. For example, installd might fork dex2oat and
    // it can be executed for minutes.
    if (entry.parent_pid() == arc_init_pid) {
      const base::ProcessId child_pid = entry.pid();
      const base::ProcessId child_nspid =
          base::Process(child_pid).GetPidInNamespace();
      if (child_nspid != base::kNullProcessId) {
        const std::string& process_name = entry.cmd_line_args()[0];
        // The is_focused and last_activity_time is not needed thus mocked
        ret_processes.emplace_back(child_nspid, child_pid, process_name,
                                   mojom::ProcessState::PERSISTENT, kNotFocused,
                                   kNoActivityTimeInfo);
      }
    }
  }
  return ret_processes;
}

void UpdateNspidToPidMap(
    scoped_refptr<ArcProcessService::NSPidToPidMap> pid_map) {
  TRACE_EVENT0("browser", "ArcProcessService::UpdateNspidToPidMap");

  // NB: Despite of its name, ProcessIterator::Snapshot() may return
  // inconsistent information because it simply walks procfs. Especially
  // we must not assume the parent-child relationships are consistent.
  const base::ProcessIterator::ProcessEntries& entry_list =
      base::ProcessIterator(nullptr).Snapshot();

  // Construct the process tree.
  // NB: This can contain a loop in case of race conditions.
  std::unordered_map<ProcessId, std::vector<ProcessId>> process_tree;
  for (const base::ProcessEntry& entry : entry_list)
    process_tree[entry.parent_pid()].push_back(entry.pid());

  ProcessId arc_init_pid = GetArcInitProcessId(entry_list);

  // Enumerate all processes under ARC init and create nspid -> pid map.
  if (arc_init_pid != kNullProcessId) {
    std::queue<ProcessId> queue;
    std::unordered_set<ProcessId> visited;
    queue.push(arc_init_pid);
    while (!queue.empty()) {
      ProcessId pid = queue.front();
      queue.pop();
      // Do not visit the same process twice. Otherwise we may enter an infinite
      // loop if |process_tree| contains a loop.
      if (!visited.insert(pid).second)
        continue;

      const ProcessId nspid = base::Process(pid).GetPidInNamespace();

      // All ARC processes should be in namespace so nspid is usually non-null,
      // but this can happen if the process has already gone.
      // Only add processes we're interested in (those appear as keys in
      // |pid_map|).
      if (nspid != kNullProcessId && pid_map->find(nspid) != pid_map->end())
        (*pid_map)[nspid] = pid;

      for (ProcessId child_pid : process_tree[pid])
        queue.push(child_pid);
    }
  }
}

std::vector<ArcProcess> FilterProcessList(
    const ArcProcessService::NSPidToPidMap& pid_map,
    std::vector<mojom::RunningAppProcessInfoPtr> processes) {
  std::vector<ArcProcess> ret_processes;
  for (const auto& entry : processes) {
    const auto it = pid_map.find(entry->pid);
    // The nspid could be missing due to race condition. For example, the
    // process is still running when we get the process snapshot and ends when
    // we update the nspid to pid mapping.
    if (it == pid_map.end() || it->second == base::kNullProcessId) {
      continue;
    }
    // Constructs the ArcProcess instance if the mapping is found.
    ArcProcess arc_process(entry->pid, pid_map.at(entry->pid),
                           entry->process_name, entry->process_state,
                           entry->is_focused, entry->last_activity_time);
    // |entry->packages| is provided only when process.mojom's verion is >=4.
    if (entry->packages) {
      for (const auto& package : *entry->packages) {
        arc_process.packages().push_back(package);
      }
    }
    ret_processes.push_back(std::move(arc_process));
  }
  return ret_processes;
}

std::vector<ArcProcess> UpdateAndReturnProcessList(
    scoped_refptr<ArcProcessService::NSPidToPidMap> nspid_map,
    std::vector<mojom::RunningAppProcessInfoPtr> processes) {
  ArcProcessService::NSPidToPidMap& pid_map = *nspid_map;
  // Cleanup dead pids in the cache |pid_map|.
  std::unordered_set<ProcessId> nspid_to_remove;
  for (const auto& entry : pid_map) {
    nspid_to_remove.insert(entry.first);
  }
  bool unmapped_nspid = false;
  for (const auto& entry : processes) {
    // erase() returns 0 if coudln't find the key. It means a new process.
    if (nspid_to_remove.erase(entry->pid) == 0) {
      pid_map[entry->pid] = base::kNullProcessId;
      unmapped_nspid = true;
    }
  }
  for (const auto& entry : nspid_to_remove) {
    pid_map.erase(entry);
  }

  // The operation is costly so avoid calling it when possible.
  if (unmapped_nspid) {
    UpdateNspidToPidMap(nspid_map);
  }

  return FilterProcessList(pid_map, std::move(processes));
}

void Reset(scoped_refptr<ArcProcessService::NSPidToPidMap> pid_map) {
  if (pid_map.get())
    pid_map->clear();
}

}  // namespace

ArcProcessService::ArcProcessService(ArcBridgeService* bridge_service)
    : ArcService(bridge_service),
      nspid_to_pid_(new NSPidToPidMap()),
      weak_ptr_factory_(this) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  auto* blocking_pool = content::BrowserThread::GetBlockingPool();
  task_runner_ = blocking_pool->GetSequencedTaskRunnerWithShutdownBehavior(
      blocking_pool->GetSequenceToken(),
      base::SequencedWorkerPool::SKIP_ON_SHUTDOWN);
  arc_bridge_service()->process()->AddObserver(this);
  DCHECK(!g_arc_process_service);
  g_arc_process_service = this;
}

ArcProcessService::~ArcProcessService() {
  DCHECK(g_arc_process_service == this);
  g_arc_process_service = nullptr;
  arc_bridge_service()->process()->RemoveObserver(this);
}

// static
ArcProcessService* ArcProcessService::Get() {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  return g_arc_process_service;
}

void ArcProcessService::RequestSystemProcessList(
    RequestProcessListCallback callback) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

  base::PostTaskAndReplyWithResult(task_runner_.get(), FROM_HERE,
                                   base::Bind(&GetArcSystemProcessList),
                                   callback);
}

bool ArcProcessService::RequestAppProcessList(
    RequestProcessListCallback callback) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

  // Since several services call this class to get information about the ARC
  // process list, it can produce a lot of logspam when the board is ARC-ready
  // but the user has not opted into ARC. This redundant check avoids that
  // logspam.
  if (!instance_ready_)
    return false;

  mojom::ProcessInstance* process_instance = ARC_GET_INSTANCE_FOR_METHOD(
      arc_bridge_service()->process(), RequestProcessList);
  if (!process_instance)
    return false;

  process_instance->RequestProcessList(
      base::Bind(&ArcProcessService::OnReceiveProcessList,
                 weak_ptr_factory_.GetWeakPtr(), callback));
  return true;
}

void ArcProcessService::OnReceiveProcessList(
    const RequestProcessListCallback& callback,
    std::vector<mojom::RunningAppProcessInfoPtr> instance_processes) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);

  base::PostTaskAndReplyWithResult(
      task_runner_.get(), FROM_HERE,
      base::Bind(&UpdateAndReturnProcessList, nspid_to_pid_,
                 base::Passed(&instance_processes)),
      callback);
}

void ArcProcessService::OnInstanceReady() {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  task_runner_->PostTask(FROM_HERE, base::Bind(&Reset, nspid_to_pid_));
  instance_ready_ = true;
}

void ArcProcessService::OnInstanceClosed() {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  instance_ready_ = false;
}

inline ArcProcessService::NSPidToPidMap::NSPidToPidMap() {}

inline ArcProcessService::NSPidToPidMap::~NSPidToPidMap() {}

}  // namespace arc