src/traced/probes/ps/process_stats_data_source.cc - platform/external/perfetto - Git at Google

 /*
  * Copyright (C) 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "src/traced/probes/ps/process_stats_data_source.h"

 #include <stdlib.h>

 #include <algorithm>
 #include <utility>

 #include "perfetto/base/file_utils.h"
 #include "perfetto/base/metatrace.h"
 #include "perfetto/base/scoped_file.h"
 #include "perfetto/base/string_splitter.h"
 #include "perfetto/base/task_runner.h"
 #include "perfetto/base/time.h"

 #include "perfetto/trace/ps/process_stats.pbzero.h"
 #include "perfetto/trace/ps/process_tree.pbzero.h"
 #include "perfetto/trace/trace_packet.pbzero.h"

 // TODO(primiano): the code in this file assumes that PIDs are never recycled
 // and that processes/threads never change names. Neither is always true.

 // The notion of PID in the Linux kernel is a bit confusing.
 // - PID: is really the thread id (for the main thread: PID == TID).
 // - TGID (thread group ID): is the Unix Process ID (the actual PID).
 // - PID == TGID for the main thread: the TID of the main thread is also the PID
 //   of the process.
 // So, in this file, |pid| might refer to either a process id or a thread id.

 namespace perfetto {

 namespace {

 inline int32_t ParseIntValue(const char* str) {
   int32_t ret = 0;
   for (;;) {
     char c = *(str++);
     if (!c)
       break;
     if (c < '0' || c > '9')
       return 0;
     ret *= 10;
     ret += static_cast<int32_t>(c - '0');
   }
   return ret;
 }

 int32_t ReadNextNumericDir(DIR* dirp) {
   while (struct dirent* dir_ent = readdir(dirp)) {
     if (dir_ent->d_type != DT_DIR)
       continue;
     int32_t int_value = ParseIntValue(dir_ent->d_name);
     if (int_value)
       return int_value;
   }
   return 0;
 }

 inline int ToInt(const std::string& str) {
   return atoi(str.c_str());
 }

 inline uint32_t ToU32(const char* str) {
   return static_cast<uint32_t>(strtol(str, nullptr, 10));
 }

 }  // namespace

 // static
 constexpr int ProcessStatsDataSource::kTypeId;

 ProcessStatsDataSource::ProcessStatsDataSource(
     base::TaskRunner* task_runner,
     TracingSessionID session_id,
     std::unique_ptr<TraceWriter> writer,
     const DataSourceConfig& config)
     : ProbesDataSource(session_id, kTypeId),
       task_runner_(task_runner),
       writer_(std::move(writer)),
       record_thread_names_(config.process_stats_config().record_thread_names()),
       dump_all_procs_on_start_(
           config.process_stats_config().scan_all_processes_on_start()),
       weak_factory_(this) {
   const auto& ps_config = config.process_stats_config();
   const auto& quirks = ps_config.quirks();
   enable_on_demand_dumps_ =
       (std::find(quirks.begin(), quirks.end(),
                  ProcessStatsConfig::DISABLE_ON_DEMAND) == quirks.end());
   poll_period_ms_ = ps_config.proc_stats_poll_ms();
   if (poll_period_ms_ > 0 && poll_period_ms_ < 100) {
     PERFETTO_ILOG("proc_stats_poll_ms %" PRIu32
                   " is less than minimum of 100ms. Increasing to 100ms.",
                   poll_period_ms_);
     poll_period_ms_ = 100;
   }

   if (poll_period_ms_ > 0) {
     auto proc_stats_ttl_ms = ps_config.proc_stats_cache_ttl_ms();
     process_stats_cache_ttl_ticks_ =
         std::max(proc_stats_ttl_ms / poll_period_ms_, 1u);
   }
 }

 ProcessStatsDataSource::~ProcessStatsDataSource() = default;

 void ProcessStatsDataSource::Start() {
   if (dump_all_procs_on_start_)
     WriteAllProcesses();

   if (poll_period_ms_) {
     auto weak_this = GetWeakPtr();
     task_runner_->PostTask(std::bind(&ProcessStatsDataSource::Tick, weak_this));
   }
 }

 base::WeakPtr<ProcessStatsDataSource> ProcessStatsDataSource::GetWeakPtr()
     const {
   return weak_factory_.GetWeakPtr();
 }

 void ProcessStatsDataSource::WriteAllProcesses() {
   PERFETTO_METATRACE("WriteAllProcesses", 0);
   PERFETTO_DCHECK(!cur_ps_tree_);

   CacheProcFsScanStartTimestamp();

   base::ScopedDir proc_dir = OpenProcDir();
   if (!proc_dir)
     return;
   while (int32_t pid = ReadNextNumericDir(*proc_dir)) {
     WriteProcessOrThread(pid);
     char task_path[255];
     sprintf(task_path, "/proc/%d/task", pid);
     base::ScopedDir task_dir(opendir(task_path));
     if (!task_dir)
       continue;

     while (int32_t tid = ReadNextNumericDir(*task_dir)) {
       if (tid == pid)
         continue;
       if (record_thread_names_) {
         WriteProcessOrThread(tid);
       } else {
         // If we are not interested in thread names, there is no need to open
         // a proc file for each thread. We can save time and directly write the
         // thread record.
         WriteThread(tid, pid, /*optional_name=*/nullptr);
       }
     }
   }
   FinalizeCurPacket();
 }

 void ProcessStatsDataSource::OnPids(const std::vector<int32_t>& pids) {
   PERFETTO_METATRACE("OnPids", 0);
   if (!enable_on_demand_dumps_)
     return;
   PERFETTO_DCHECK(!cur_ps_tree_);
   for (int32_t pid : pids) {
     if (seen_pids_.count(pid) || pid == 0)
       continue;
     WriteProcessOrThread(pid);
   }
   FinalizeCurPacket();
 }

 void ProcessStatsDataSource::OnRenamePids(const std::vector<int32_t>& pids) {
   PERFETTO_METATRACE("OnRenamePids", 0);
   if (!enable_on_demand_dumps_)
     return;
   PERFETTO_DCHECK(!cur_ps_tree_);
   for (int32_t pid : pids) {
     auto pid_it = seen_pids_.find(pid);
     if (pid_it == seen_pids_.end())
       continue;
     seen_pids_.erase(pid_it);
   }
 }

 void ProcessStatsDataSource::Flush(FlushRequestID,
                                    std::function<void()> callback) {
   // We shouldn't get this in the middle of WriteAllProcesses() or OnPids().
   PERFETTO_DCHECK(!cur_ps_tree_);
   PERFETTO_DCHECK(!cur_ps_stats_);
   PERFETTO_DCHECK(!cur_ps_stats_process_);
   writer_->Flush(callback);
 }

 void ProcessStatsDataSource::WriteProcessOrThread(int32_t pid) {
   // In case we're called from outside WriteAllProcesses()
   CacheProcFsScanStartTimestamp();

   std::string proc_status = ReadProcPidFile(pid, "status");
   if (proc_status.empty())
     return;
   int tgid = ToInt(ReadProcStatusEntry(proc_status, "Tgid:"));
   if (tgid <= 0)
     return;
   if (!seen_pids_.count(tgid))
     WriteProcess(tgid, proc_status);
   if (pid != tgid) {
     PERFETTO_DCHECK(!seen_pids_.count(pid));
     std::string thread_name;
     if (record_thread_names_)
       thread_name = ReadProcStatusEntry(proc_status, "Name:");
     WriteThread(pid, tgid, thread_name.empty() ? nullptr : thread_name.c_str());
   }
 }

 void ProcessStatsDataSource::WriteProcess(int32_t pid,
                                           const std::string& proc_status) {
   PERFETTO_DCHECK(ToInt(ReadProcStatusEntry(proc_status, "Tgid:")) == pid);
   auto* proc = GetOrCreatePsTree()->add_processes();
   proc->set_pid(pid);
   proc->set_ppid(ToInt(ReadProcStatusEntry(proc_status, "PPid:")));

   std::string cmdline = ReadProcPidFile(pid, "cmdline");
   if (!cmdline.empty()) {
     using base::StringSplitter;
     for (StringSplitter ss(&cmdline[0], cmdline.size(), '\0'); ss.Next();)
       proc->add_cmdline(ss.cur_token());
   } else {
     // Nothing in cmdline so use the thread name instead (which is == "comm").
     proc->add_cmdline(ReadProcStatusEntry(proc_status, "Name:").c_str());
   }
   seen_pids_.emplace(pid);
 }

 void ProcessStatsDataSource::WriteThread(int32_t tid,
                                          int32_t tgid,
                                          const char* optional_name) {
   auto* thread = GetOrCreatePsTree()->add_threads();
   thread->set_tid(tid);
   thread->set_tgid(tgid);
   if (optional_name)
     thread->set_name(optional_name);
   seen_pids_.emplace(tid);
 }

 base::ScopedDir ProcessStatsDataSource::OpenProcDir() {
   base::ScopedDir proc_dir(opendir("/proc"));
   if (!proc_dir)
     PERFETTO_PLOG("Failed to opendir(/proc)");
   return proc_dir;
 }

 std::string ProcessStatsDataSource::ReadProcPidFile(int32_t pid,
                                                     const std::string& file) {
   std::string contents;
   contents.reserve(4096);
   if (!base::ReadFile("/proc/" + std::to_string(pid) + "/" + file, &contents))
     return "";
   return contents;
 }

 std::string ProcessStatsDataSource::ReadProcStatusEntry(const std::string& buf,
                                                         const char* key) {
   auto begin = buf.find(key);
   if (begin == std::string::npos)
     return "";
   begin = buf.find_first_not_of(" \t", begin + strlen(key));
   if (begin == std::string::npos)
     return "";
   auto end = buf.find('\n', begin);
   if (end == std::string::npos || end <= begin)
     return "";
   return buf.substr(begin, end - begin);
 }

 void ProcessStatsDataSource::StartNewPacketIfNeeded() {
   if (cur_packet_)
     return;
   cur_packet_ = writer_->NewTracePacket();
   cur_packet_->set_timestamp(CacheProcFsScanStartTimestamp());

   if (did_clear_incremental_state_) {
     cur_packet_->set_incremental_state_cleared(true);
     did_clear_incremental_state_ = false;
   }
 }

 protos::pbzero::ProcessTree* ProcessStatsDataSource::GetOrCreatePsTree() {
   StartNewPacketIfNeeded();
   if (!cur_ps_tree_)
     cur_ps_tree_ = cur_packet_->set_process_tree();
   cur_ps_stats_ = nullptr;
   cur_ps_stats_process_ = nullptr;
   return cur_ps_tree_;
 }

 protos::pbzero::ProcessStats* ProcessStatsDataSource::GetOrCreateStats() {
   StartNewPacketIfNeeded();
   if (!cur_ps_stats_)
     cur_ps_stats_ = cur_packet_->set_process_stats();
   cur_ps_tree_ = nullptr;
   cur_ps_stats_process_ = nullptr;
   return cur_ps_stats_;
 }

 protos::pbzero::ProcessStats_Process*
 ProcessStatsDataSource::GetOrCreateStatsProcess(int32_t pid) {
   if (cur_ps_stats_process_)
     return cur_ps_stats_process_;
   cur_ps_stats_process_ = GetOrCreateStats()->add_processes();
   cur_ps_stats_process_->set_pid(pid);
   return cur_ps_stats_process_;
 }

 void ProcessStatsDataSource::FinalizeCurPacket() {
   PERFETTO_DCHECK(!cur_ps_tree_ || cur_packet_);
   PERFETTO_DCHECK(!cur_ps_stats_ || cur_packet_);
   uint64_t now = static_cast<uint64_t>(base::GetBootTimeNs().count());
   if (cur_ps_tree_) {
     cur_ps_tree_->set_collection_end_timestamp(now);
     cur_ps_tree_ = nullptr;
   }
   if (cur_ps_stats_) {
     cur_ps_stats_->set_collection_end_timestamp(now);
     cur_ps_stats_ = nullptr;
   }
   cur_ps_stats_process_ = nullptr;
   cur_procfs_scan_start_timestamp_ = 0;
   cur_packet_ = TraceWriter::TracePacketHandle{};
 }

 // static
 void ProcessStatsDataSource::Tick(
     base::WeakPtr<ProcessStatsDataSource> weak_this) {
   if (!weak_this)
     return;
   ProcessStatsDataSource& thiz = *weak_this;
   uint32_t period_ms = thiz.poll_period_ms_;
   uint32_t delay_ms = period_ms - (base::GetWallTimeMs().count() % period_ms);
   thiz.task_runner_->PostDelayedTask(
       std::bind(&ProcessStatsDataSource::Tick, weak_this), delay_ms);
   thiz.WriteAllProcessStats();

   // We clear the cache every process_stats_cache_ttl_ticks_ ticks.
   if (++thiz.cache_ticks_ == thiz.process_stats_cache_ttl_ticks_) {
     thiz.cache_ticks_ = 0;
     thiz.process_stats_cache_.clear();
   }
 }

 void ProcessStatsDataSource::WriteAllProcessStats() {
   // TODO(primiano): implement whitelisting of processes by names.
   // TODO(primiano): Have a pid cache to avoid wasting cycles reading kthreads
   // proc files over and over. Same for non-whitelist processes (see above).

   CacheProcFsScanStartTimestamp();
   PERFETTO_METATRACE("WriteAllProcessStats", 0);
   base::ScopedDir proc_dir = OpenProcDir();
   if (!proc_dir)
     return;
   std::vector<int32_t> pids;
   while (int32_t pid = ReadNextNumericDir(*proc_dir)) {
     cur_ps_stats_process_ = nullptr;

     uint32_t pid_u = static_cast<uint32_t>(pid);
     if (skip_stats_for_pids_.size() > pid_u && skip_stats_for_pids_[pid_u])
       continue;

     std::string proc_status = ReadProcPidFile(pid, "status");
     if (proc_status.empty())
       continue;

     if (!WriteMemCounters(pid, proc_status)) {
       // If WriteMemCounters() fails the pid is very likely a kernel thread
       // that has a valid /proc/[pid]/status but no memory values. In this
       // case avoid keep polling it over and over.
       if (skip_stats_for_pids_.size() <= pid_u)
         skip_stats_for_pids_.resize(pid_u + 1);
       skip_stats_for_pids_[pid_u] = true;
       continue;
     }

     std::string oom_score_adj = ReadProcPidFile(pid, "oom_score_adj");
     if (!oom_score_adj.empty()) {
       CachedProcessStats& cached = process_stats_cache_[pid];
       auto counter = ToInt(oom_score_adj);
       if (counter != cached.oom_score_adj) {
         GetOrCreateStatsProcess(pid)->set_oom_score_adj(counter);
         cached.oom_score_adj = counter;
       }
     }

     pids.push_back(pid);
   }
   FinalizeCurPacket();

   // Ensure that we write once long-term process info (e.g., name) for new pids
   // that we haven't seen before.
   OnPids(pids);
 }

 // Returns true if the stats for the given |pid| have been written, false it
 // it failed (e.g., |pid| was a kernel thread and, as such, didn't report any
 // memory counters).
 bool ProcessStatsDataSource::WriteMemCounters(int32_t pid,
                                               const std::string& proc_status) {
   bool proc_status_has_mem_counters = false;
   CachedProcessStats& cached = process_stats_cache_[pid];

   // Parse /proc/[pid]/status, which looks like this:
   // Name:   cat
   // Umask:  0027
   // State:  R (running)
   // FDSize: 256
   // Groups: 4 20 24 46 997
   // VmPeak:     5992 kB
   // VmSize:     5992 kB
   // VmLck:         0 kB
   // ...
   std::vector<char> key;
   std::vector<char> value;
   enum { kKey, kSeparator, kValue } state = kKey;
   for (char c : proc_status) {
     if (c == '\n') {
       key.push_back('\0');
       value.push_back('\0');

       // |value| will contain "1234 KB". We rely on strtol() (in ToU32()) to
       // stop parsing at the first non-numeric character.
       if (strcmp(key.data(), "VmSize") == 0) {
         // Assume that if we see VmSize we'll see also the others.
         proc_status_has_mem_counters = true;

         auto counter = ToU32(value.data());
         if (counter != cached.vm_size_kb) {
           GetOrCreateStatsProcess(pid)->set_vm_size_kb(counter);
           cached.vm_size_kb = counter;
         }
       } else if (strcmp(key.data(), "VmLck") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.vm_locked_kb) {
           GetOrCreateStatsProcess(pid)->set_vm_locked_kb(counter);
           cached.vm_locked_kb = counter;
         }
       } else if (strcmp(key.data(), "VmHWM") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.vm_hvm_kb) {
           GetOrCreateStatsProcess(pid)->set_vm_hwm_kb(counter);
           cached.vm_hvm_kb = counter;
         }
       } else if (strcmp(key.data(), "VmRSS") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.vm_rss_kb) {
           GetOrCreateStatsProcess(pid)->set_vm_rss_kb(counter);
           cached.vm_rss_kb = counter;
         }
       } else if (strcmp(key.data(), "RssAnon") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.rss_anon_kb) {
           GetOrCreateStatsProcess(pid)->set_rss_anon_kb(counter);
           cached.rss_anon_kb = counter;
         }
       } else if (strcmp(key.data(), "RssFile") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.rss_file_kb) {
           GetOrCreateStatsProcess(pid)->set_rss_file_kb(counter);
           cached.rss_file_kb = counter;
         }
       } else if (strcmp(key.data(), "RssShmem") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.rss_shmem_kb) {
           GetOrCreateStatsProcess(pid)->set_rss_shmem_kb(counter);
           cached.rss_shmem_kb = counter;
         }
       } else if (strcmp(key.data(), "VmSwap") == 0) {
         auto counter = ToU32(value.data());
         if (counter != cached.vm_swap_kb) {
           GetOrCreateStatsProcess(pid)->set_vm_swap_kb(counter);
           cached.vm_swap_kb = counter;
         }
       }

       key.clear();
       state = kKey;
       continue;
     }

     if (state == kKey) {
       if (c == ':') {
         state = kSeparator;
         continue;
       }
       key.push_back(c);
       continue;
     }

     if (state == kSeparator) {
       if (isspace(c))
         continue;
       value.clear();
       value.push_back(c);
       state = kValue;
       continue;
     }

     if (state == kValue) {
       value.push_back(c);
     }
   }
   return proc_status_has_mem_counters;
 }

 uint64_t ProcessStatsDataSource::CacheProcFsScanStartTimestamp() {
   if (!cur_procfs_scan_start_timestamp_)
     cur_procfs_scan_start_timestamp_ =
         static_cast<uint64_t>(base::GetBootTimeNs().count());
   return cur_procfs_scan_start_timestamp_;
 }

 void ProcessStatsDataSource::ClearIncrementalState() {
   PERFETTO_DLOG("ProcessStatsDataSource clearing incremental state.");
   seen_pids_.clear();
   skip_stats_for_pids_.clear();

   cache_ticks_ = 0;
   process_stats_cache_.clear();

   // Set the relevant flag in the next packet.
   did_clear_incremental_state_ = true;
 }

 }  // namespace perfetto
	/*
	* Copyright (C) 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "src/traced/probes/ps/process_stats_data_source.h"

	#include <stdlib.h>

	#include <algorithm>
	#include <utility>

	#include "perfetto/base/file_utils.h"
	#include "perfetto/base/metatrace.h"
	#include "perfetto/base/scoped_file.h"
	#include "perfetto/base/string_splitter.h"
	#include "perfetto/base/task_runner.h"
	#include "perfetto/base/time.h"

	#include "perfetto/trace/ps/process_stats.pbzero.h"
	#include "perfetto/trace/ps/process_tree.pbzero.h"
	#include "perfetto/trace/trace_packet.pbzero.h"

	// TODO(primiano): the code in this file assumes that PIDs are never recycled
	// and that processes/threads never change names. Neither is always true.

	// The notion of PID in the Linux kernel is a bit confusing.
	// - PID: is really the thread id (for the main thread: PID == TID).
	// - TGID (thread group ID): is the Unix Process ID (the actual PID).
	// - PID == TGID for the main thread: the TID of the main thread is also the PID
	// of the process.
	// So, in this file, \|pid\| might refer to either a process id or a thread id.

	namespace perfetto {

	namespace {

	inline int32_t ParseIntValue(const char* str) {
	int32_t ret = 0;
	for (;;) {
	char c = *(str++);
	if (!c)
	break;
	if (c < '0' \|\| c > '9')
	return 0;
	ret *= 10;
	ret += static_cast<int32_t>(c - '0');
	}
	return ret;
	}

	int32_t ReadNextNumericDir(DIR* dirp) {
	while (struct dirent* dir_ent = readdir(dirp)) {
	if (dir_ent->d_type != DT_DIR)
	continue;
	int32_t int_value = ParseIntValue(dir_ent->d_name);
	if (int_value)
	return int_value;
	}
	return 0;
	}

	inline int ToInt(const std::string& str) {
	return atoi(str.c_str());
	}

	inline uint32_t ToU32(const char* str) {
	return static_cast<uint32_t>(strtol(str, nullptr, 10));
	}

	} // namespace

	// static
	constexpr int ProcessStatsDataSource::kTypeId;

	ProcessStatsDataSource::ProcessStatsDataSource(
	base::TaskRunner* task_runner,
	TracingSessionID session_id,
	std::unique_ptr<TraceWriter> writer,
	const DataSourceConfig& config)
	: ProbesDataSource(session_id, kTypeId),
	task_runner_(task_runner),
	writer_(std::move(writer)),
	record_thread_names_(config.process_stats_config().record_thread_names()),
	dump_all_procs_on_start_(
	config.process_stats_config().scan_all_processes_on_start()),
	weak_factory_(this) {
	const auto& ps_config = config.process_stats_config();
	const auto& quirks = ps_config.quirks();
	enable_on_demand_dumps_ =
	(std::find(quirks.begin(), quirks.end(),
	ProcessStatsConfig::DISABLE_ON_DEMAND) == quirks.end());
	poll_period_ms_ = ps_config.proc_stats_poll_ms();
	if (poll_period_ms_ > 0 && poll_period_ms_ < 100) {
	PERFETTO_ILOG("proc_stats_poll_ms %" PRIu32
	" is less than minimum of 100ms. Increasing to 100ms.",
	poll_period_ms_);
	poll_period_ms_ = 100;
	}

	if (poll_period_ms_ > 0) {
	auto proc_stats_ttl_ms = ps_config.proc_stats_cache_ttl_ms();
	process_stats_cache_ttl_ticks_ =
	std::max(proc_stats_ttl_ms / poll_period_ms_, 1u);
	}
	}

	ProcessStatsDataSource::~ProcessStatsDataSource() = default;

	void ProcessStatsDataSource::Start() {
	if (dump_all_procs_on_start_)
	WriteAllProcesses();

	if (poll_period_ms_) {
	auto weak_this = GetWeakPtr();
	task_runner_->PostTask(std::bind(&ProcessStatsDataSource::Tick, weak_this));
	}
	}

	base::WeakPtr<ProcessStatsDataSource> ProcessStatsDataSource::GetWeakPtr()
	const {
	return weak_factory_.GetWeakPtr();
	}

	void ProcessStatsDataSource::WriteAllProcesses() {
	PERFETTO_METATRACE("WriteAllProcesses", 0);
	PERFETTO_DCHECK(!cur_ps_tree_);

	CacheProcFsScanStartTimestamp();

	base::ScopedDir proc_dir = OpenProcDir();
	if (!proc_dir)
	return;
	while (int32_t pid = ReadNextNumericDir(*proc_dir)) {
	WriteProcessOrThread(pid);
	char task_path[255];
	sprintf(task_path, "/proc/%d/task", pid);
	base::ScopedDir task_dir(opendir(task_path));
	if (!task_dir)
	continue;

	while (int32_t tid = ReadNextNumericDir(*task_dir)) {
	if (tid == pid)
	continue;
	if (record_thread_names_) {
	WriteProcessOrThread(tid);
	} else {
	// If we are not interested in thread names, there is no need to open
	// a proc file for each thread. We can save time and directly write the
	// thread record.
	WriteThread(tid, pid, /optional_name=/nullptr);
	}
	}
	}
	FinalizeCurPacket();
	}

	void ProcessStatsDataSource::OnPids(const std::vector<int32_t>& pids) {
	PERFETTO_METATRACE("OnPids", 0);
	if (!enable_on_demand_dumps_)
	return;
	PERFETTO_DCHECK(!cur_ps_tree_);
	for (int32_t pid : pids) {
	if (seen_pids_.count(pid) \|\| pid == 0)
	continue;
	WriteProcessOrThread(pid);
	}
	FinalizeCurPacket();
	}

	void ProcessStatsDataSource::OnRenamePids(const std::vector<int32_t>& pids) {
	PERFETTO_METATRACE("OnRenamePids", 0);
	if (!enable_on_demand_dumps_)
	return;
	PERFETTO_DCHECK(!cur_ps_tree_);
	for (int32_t pid : pids) {
	auto pid_it = seen_pids_.find(pid);
	if (pid_it == seen_pids_.end())
	continue;
	seen_pids_.erase(pid_it);
	}
	}

	void ProcessStatsDataSource::Flush(FlushRequestID,
	std::function<void()> callback) {
	// We shouldn't get this in the middle of WriteAllProcesses() or OnPids().
	PERFETTO_DCHECK(!cur_ps_tree_);
	PERFETTO_DCHECK(!cur_ps_stats_);
	PERFETTO_DCHECK(!cur_ps_stats_process_);
	writer_->Flush(callback);
	}

	void ProcessStatsDataSource::WriteProcessOrThread(int32_t pid) {
	// In case we're called from outside WriteAllProcesses()
	CacheProcFsScanStartTimestamp();

	std::string proc_status = ReadProcPidFile(pid, "status");
	if (proc_status.empty())
	return;
	int tgid = ToInt(ReadProcStatusEntry(proc_status, "Tgid:"));
	if (tgid <= 0)
	return;
	if (!seen_pids_.count(tgid))
	WriteProcess(tgid, proc_status);
	if (pid != tgid) {
	PERFETTO_DCHECK(!seen_pids_.count(pid));
	std::string thread_name;
	if (record_thread_names_)
	thread_name = ReadProcStatusEntry(proc_status, "Name:");
	WriteThread(pid, tgid, thread_name.empty() ? nullptr : thread_name.c_str());
	}
	}

	void ProcessStatsDataSource::WriteProcess(int32_t pid,
	const std::string& proc_status) {
	PERFETTO_DCHECK(ToInt(ReadProcStatusEntry(proc_status, "Tgid:")) == pid);
	auto* proc = GetOrCreatePsTree()->add_processes();
	proc->set_pid(pid);
	proc->set_ppid(ToInt(ReadProcStatusEntry(proc_status, "PPid:")));

	std::string cmdline = ReadProcPidFile(pid, "cmdline");
	if (!cmdline.empty()) {
	using base::StringSplitter;
	for (StringSplitter ss(&cmdline[0], cmdline.size(), '\0'); ss.Next();)
	proc->add_cmdline(ss.cur_token());
	} else {
	// Nothing in cmdline so use the thread name instead (which is == "comm").
	proc->add_cmdline(ReadProcStatusEntry(proc_status, "Name:").c_str());
	}
	seen_pids_.emplace(pid);
	}

	void ProcessStatsDataSource::WriteThread(int32_t tid,
	int32_t tgid,
	const char* optional_name) {
	auto* thread = GetOrCreatePsTree()->add_threads();
	thread->set_tid(tid);
	thread->set_tgid(tgid);
	if (optional_name)
	thread->set_name(optional_name);
	seen_pids_.emplace(tid);
	}

	base::ScopedDir ProcessStatsDataSource::OpenProcDir() {
	base::ScopedDir proc_dir(opendir("/proc"));
	if (!proc_dir)
	PERFETTO_PLOG("Failed to opendir(/proc)");
	return proc_dir;
	}

	std::string ProcessStatsDataSource::ReadProcPidFile(int32_t pid,
	const std::string& file) {
	std::string contents;
	contents.reserve(4096);
	if (!base::ReadFile("/proc/" + std::to_string(pid) + "/" + file, &contents))
	return "";
	return contents;
	}

	std::string ProcessStatsDataSource::ReadProcStatusEntry(const std::string& buf,
	const char* key) {
	auto begin = buf.find(key);
	if (begin == std::string::npos)
	return "";
	begin = buf.find_first_not_of(" \t", begin + strlen(key));
	if (begin == std::string::npos)
	return "";
	auto end = buf.find('\n', begin);
	if (end == std::string::npos \|\| end <= begin)
	return "";
	return buf.substr(begin, end - begin);
	}

	void ProcessStatsDataSource::StartNewPacketIfNeeded() {
	if (cur_packet_)
	return;
	cur_packet_ = writer_->NewTracePacket();
	cur_packet_->set_timestamp(CacheProcFsScanStartTimestamp());

	if (did_clear_incremental_state_) {
	cur_packet_->set_incremental_state_cleared(true);
	did_clear_incremental_state_ = false;
	}
	}

	protos::pbzero::ProcessTree* ProcessStatsDataSource::GetOrCreatePsTree() {
	StartNewPacketIfNeeded();
	if (!cur_ps_tree_)
	cur_ps_tree_ = cur_packet_->set_process_tree();
	cur_ps_stats_ = nullptr;
	cur_ps_stats_process_ = nullptr;
	return cur_ps_tree_;
	}

	protos::pbzero::ProcessStats* ProcessStatsDataSource::GetOrCreateStats() {
	StartNewPacketIfNeeded();
	if (!cur_ps_stats_)
	cur_ps_stats_ = cur_packet_->set_process_stats();
	cur_ps_tree_ = nullptr;
	cur_ps_stats_process_ = nullptr;
	return cur_ps_stats_;
	}

	protos::pbzero::ProcessStats_Process*
	ProcessStatsDataSource::GetOrCreateStatsProcess(int32_t pid) {
	if (cur_ps_stats_process_)
	return cur_ps_stats_process_;
	cur_ps_stats_process_ = GetOrCreateStats()->add_processes();
	cur_ps_stats_process_->set_pid(pid);
	return cur_ps_stats_process_;
	}

	void ProcessStatsDataSource::FinalizeCurPacket() {
	PERFETTO_DCHECK(!cur_ps_tree_ \|\| cur_packet_);
	PERFETTO_DCHECK(!cur_ps_stats_ \|\| cur_packet_);
	uint64_t now = static_cast<uint64_t>(base::GetBootTimeNs().count());
	if (cur_ps_tree_) {
	cur_ps_tree_->set_collection_end_timestamp(now);
	cur_ps_tree_ = nullptr;
	}
	if (cur_ps_stats_) {
	cur_ps_stats_->set_collection_end_timestamp(now);
	cur_ps_stats_ = nullptr;
	}
	cur_ps_stats_process_ = nullptr;
	cur_procfs_scan_start_timestamp_ = 0;
	cur_packet_ = TraceWriter::TracePacketHandle{};
	}

	// static
	void ProcessStatsDataSource::Tick(
	base::WeakPtr<ProcessStatsDataSource> weak_this) {
	if (!weak_this)
	return;
	ProcessStatsDataSource& thiz = *weak_this;
	uint32_t period_ms = thiz.poll_period_ms_;
	uint32_t delay_ms = period_ms - (base::GetWallTimeMs().count() % period_ms);
	thiz.task_runner_->PostDelayedTask(
	std::bind(&ProcessStatsDataSource::Tick, weak_this), delay_ms);
	thiz.WriteAllProcessStats();

	// We clear the cache every process_stats_cache_ttl_ticks_ ticks.
	if (++thiz.cache_ticks_ == thiz.process_stats_cache_ttl_ticks_) {
	thiz.cache_ticks_ = 0;
	thiz.process_stats_cache_.clear();
	}
	}

	void ProcessStatsDataSource::WriteAllProcessStats() {
	// TODO(primiano): implement whitelisting of processes by names.
	// TODO(primiano): Have a pid cache to avoid wasting cycles reading kthreads
	// proc files over and over. Same for non-whitelist processes (see above).

	CacheProcFsScanStartTimestamp();
	PERFETTO_METATRACE("WriteAllProcessStats", 0);
	base::ScopedDir proc_dir = OpenProcDir();
	if (!proc_dir)
	return;
	std::vector<int32_t> pids;
	while (int32_t pid = ReadNextNumericDir(*proc_dir)) {
	cur_ps_stats_process_ = nullptr;

	uint32_t pid_u = static_cast<uint32_t>(pid);
	if (skip_stats_for_pids_.size() > pid_u && skip_stats_for_pids_[pid_u])
	continue;

	std::string proc_status = ReadProcPidFile(pid, "status");
	if (proc_status.empty())
	continue;

	if (!WriteMemCounters(pid, proc_status)) {
	// If WriteMemCounters() fails the pid is very likely a kernel thread
	// that has a valid /proc/[pid]/status but no memory values. In this
	// case avoid keep polling it over and over.
	if (skip_stats_for_pids_.size() <= pid_u)
	skip_stats_for_pids_.resize(pid_u + 1);
	skip_stats_for_pids_[pid_u] = true;
	continue;
	}

	std::string oom_score_adj = ReadProcPidFile(pid, "oom_score_adj");
	if (!oom_score_adj.empty()) {
	CachedProcessStats& cached = process_stats_cache_[pid];
	auto counter = ToInt(oom_score_adj);
	if (counter != cached.oom_score_adj) {
	GetOrCreateStatsProcess(pid)->set_oom_score_adj(counter);
	cached.oom_score_adj = counter;
	}
	}

	pids.push_back(pid);
	}
	FinalizeCurPacket();

	// Ensure that we write once long-term process info (e.g., name) for new pids
	// that we haven't seen before.
	OnPids(pids);
	}

	// Returns true if the stats for the given \|pid\| have been written, false it
	// it failed (e.g., \|pid\| was a kernel thread and, as such, didn't report any
	// memory counters).
	bool ProcessStatsDataSource::WriteMemCounters(int32_t pid,
	const std::string& proc_status) {
	bool proc_status_has_mem_counters = false;
	CachedProcessStats& cached = process_stats_cache_[pid];

	// Parse /proc/[pid]/status, which looks like this:
	// Name: cat
	// Umask: 0027
	// State: R (running)
	// FDSize: 256
	// Groups: 4 20 24 46 997
	// VmPeak: 5992 kB
	// VmSize: 5992 kB
	// VmLck: 0 kB
	// ...
	std::vector<char> key;
	std::vector<char> value;
	enum { kKey, kSeparator, kValue } state = kKey;
	for (char c : proc_status) {
	if (c == '\n') {
	key.push_back('\0');
	value.push_back('\0');

	// \|value\| will contain "1234 KB". We rely on strtol() (in ToU32()) to
	// stop parsing at the first non-numeric character.
	if (strcmp(key.data(), "VmSize") == 0) {
	// Assume that if we see VmSize we'll see also the others.
	proc_status_has_mem_counters = true;

	auto counter = ToU32(value.data());
	if (counter != cached.vm_size_kb) {
	GetOrCreateStatsProcess(pid)->set_vm_size_kb(counter);
	cached.vm_size_kb = counter;
	}
	} else if (strcmp(key.data(), "VmLck") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.vm_locked_kb) {
	GetOrCreateStatsProcess(pid)->set_vm_locked_kb(counter);
	cached.vm_locked_kb = counter;
	}
	} else if (strcmp(key.data(), "VmHWM") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.vm_hvm_kb) {
	GetOrCreateStatsProcess(pid)->set_vm_hwm_kb(counter);
	cached.vm_hvm_kb = counter;
	}
	} else if (strcmp(key.data(), "VmRSS") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.vm_rss_kb) {
	GetOrCreateStatsProcess(pid)->set_vm_rss_kb(counter);
	cached.vm_rss_kb = counter;
	}
	} else if (strcmp(key.data(), "RssAnon") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.rss_anon_kb) {
	GetOrCreateStatsProcess(pid)->set_rss_anon_kb(counter);
	cached.rss_anon_kb = counter;
	}
	} else if (strcmp(key.data(), "RssFile") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.rss_file_kb) {
	GetOrCreateStatsProcess(pid)->set_rss_file_kb(counter);
	cached.rss_file_kb = counter;
	}
	} else if (strcmp(key.data(), "RssShmem") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.rss_shmem_kb) {
	GetOrCreateStatsProcess(pid)->set_rss_shmem_kb(counter);
	cached.rss_shmem_kb = counter;
	}
	} else if (strcmp(key.data(), "VmSwap") == 0) {
	auto counter = ToU32(value.data());
	if (counter != cached.vm_swap_kb) {
	GetOrCreateStatsProcess(pid)->set_vm_swap_kb(counter);
	cached.vm_swap_kb = counter;
	}
	}

	key.clear();
	state = kKey;
	continue;
	}

	if (state == kKey) {
	if (c == ':') {
	state = kSeparator;
	continue;
	}
	key.push_back(c);
	continue;
	}

	if (state == kSeparator) {
	if (isspace(c))
	continue;
	value.clear();
	value.push_back(c);
	state = kValue;
	continue;
	}

	if (state == kValue) {
	value.push_back(c);
	}
	}
	return proc_status_has_mem_counters;
	}

	uint64_t ProcessStatsDataSource::CacheProcFsScanStartTimestamp() {
	if (!cur_procfs_scan_start_timestamp_)
	cur_procfs_scan_start_timestamp_ =
	static_cast<uint64_t>(base::GetBootTimeNs().count());
	return cur_procfs_scan_start_timestamp_;
	}

	void ProcessStatsDataSource::ClearIncrementalState() {
	PERFETTO_DLOG("ProcessStatsDataSource clearing incremental state.");
	seen_pids_.clear();
	skip_stats_for_pids_.clear();

	cache_ticks_ = 0;
	process_stats_cache_.clear();

	// Set the relevant flag in the next packet.
	did_clear_incremental_state_ = true;
	}

	} // namespace perfetto