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 // Copyright (c) 2006-2008 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/stats_table.h"

 #include "base/logging.h"

 #include "base/platform_thread.h"

 #include "base/process_util.h"

 #include "base/scoped_ptr.h"

 #include "base/shared_memory.h"

 #include "base/string_piece.h"

 #include "base/string_util.h"

 #include "base/sys_string_conversions.h"

 #include "base/thread_local_storage.h"

 #if defined(OS_POSIX)

 #include "errno.h"

 #endif

 // The StatsTable uses a shared memory segment that is laid out as follows

 //

 // +-------------------------------------------+

 // | Version | Size | MaxCounters | MaxThreads |

 // +-------------------------------------------+

 // | Thread names table                        |

 // +-------------------------------------------+

 // | Thread TID table                          |

 // +-------------------------------------------+

 // | Thread PID table                          |

 // +-------------------------------------------+

 // | Counter names table                       |

 // +-------------------------------------------+

 // | Data                                      |

 // +-------------------------------------------+

 //

 // The data layout is a grid, where the columns are the thread_ids and the

 // rows are the counter_ids.

 //

 // If the first character of the thread_name is '\0', then that column is

 // empty.

 // If the first character of the counter_name is '\0', then that row is

 // empty.

 //

 // About Locking:

 // This class is designed to be both multi-thread and multi-process safe.

 // Aside from initialization, this is done by partitioning the data which

 // each thread uses so that no locking is required.  However, to allocate

 // the rows and columns of the table to particular threads, locking is

 // required.

 //

 // At the shared-memory level, we have a lock.  This lock protects the

 // shared-memory table only, and is used when we create new counters (e.g.

 // use rows) or when we register new threads (e.g. use columns).  Reading

 // data from the table does not require any locking at the shared memory

 // level.

 //

 // Each process which accesses the table will create a StatsTable object.

 // The StatsTable maintains a hash table of the existing counters in the

 // table for faster lookup.  Since the hash table is process specific,

 // each process maintains its own cache.  We avoid complexity here by never

 // de-allocating from the hash table.  (Counters are dynamically added,

 // but not dynamically removed).

 // In order for external viewers to be able to read our shared memory,

 // we all need to use the same size ints.

 COMPILE_ASSERT(sizeof(int)==4, expect_4_byte_ints);

 namespace {

 // An internal version in case we ever change the format of this

 // file, and so that we can identify our table.

 const int kTableVersion = 0x13131313;

 // The name for un-named counters and threads in the table.

 const char kUnknownName[] = "<unknown>";

 // Calculates delta to align an offset to the size of an int

 inline int AlignOffset(int offset) {

   return (sizeof(int) - (offset % sizeof(int))) % sizeof(int);

 }

 inline int AlignedSize(int size) {

   return size + AlignOffset(size);

 }

 // StatsTableTLSData carries the data stored in the TLS slots for the

 // StatsTable.  This is used so that we can properly cleanup when the

 // thread exits and return the table slot.

 //

 // Each thread that calls RegisterThread in the StatsTable will have

 // a StatsTableTLSData stored in its TLS.

 struct StatsTableTLSData {

   StatsTable* table;

   int slot;

 };

 }  // namespace

 // The StatsTablePrivate maintains convenience pointers into the

 // shared memory segment.  Use this class to keep the data structure

 // clean and accessible.

 class StatsTablePrivate {

  public:

   // Various header information contained in the memory mapped segment.

   struct TableHeader {

     int version;

     int size;

     int max_counters;

     int max_threads;

   };

   // Construct a new StatsTablePrivate based on expected size parameters, or

   // return NULL on failure.

   static StatsTablePrivate* New(const std::string& name, int size,

                                 int max_threads, int max_counters);

   base::SharedMemory* shared_memory() { return &shared_memory_; }

   // Accessors for our header pointers

   TableHeader* table_header() const { return table_header_; }

   int version() const { return table_header_->version; }

   int size() const { return table_header_->size; }

   int max_counters() const { return table_header_->max_counters; }

   int max_threads() const { return table_header_->max_threads; }

   // Accessors for our tables

   char* thread_name(int slot_id) const {

     return &thread_names_table_[

       (slot_id-1) * (StatsTable::kMaxThreadNameLength)];

   }

   PlatformThreadId* thread_tid(int slot_id) const {

     return &(thread_tid_table_[slot_id-1]);

   }

   int* thread_pid(int slot_id) const {

     return &(thread_pid_table_[slot_id-1]);

   }

   char* counter_name(int counter_id) const {

     return &counter_names_table_[

       (counter_id-1) * (StatsTable::kMaxCounterNameLength)];

   }

   int* row(int counter_id) const {

     return &data_table_[(counter_id-1) * max_threads()];

   }

  private:

   // Constructor is private because you should use New() instead.

   StatsTablePrivate() {}

   // Initializes the table on first access.  Sets header values

   // appropriately and zeroes all counters.

   void InitializeTable(void* memory, int size, int max_counters,

                        int max_threads);

   // Initializes our in-memory pointers into a pre-created StatsTable.

   void ComputeMappedPointers(void* memory);

   base::SharedMemory shared_memory_;

   TableHeader* table_header_;

   char* thread_names_table_;

   PlatformThreadId* thread_tid_table_;

   int* thread_pid_table_;

   char* counter_names_table_;

   int* data_table_;

 };

 // static

 StatsTablePrivate* StatsTablePrivate::New(const std::string& name,

                                           int size,

                                           int max_threads,

                                           int max_counters) {

   scoped_ptr<StatsTablePrivate> priv(new StatsTablePrivate());

   if (!priv->shared_memory_.Create(name, false, true, size))

     return NULL;

   if (!priv->shared_memory_.Map(size))

     return NULL;

   void* memory = priv->shared_memory_.memory();

   TableHeader* header = static_cast<TableHeader*>(memory);

   // If the version does not match, then assume the table needs

   // to be initialized.

   if (header->version != kTableVersion)

     priv->InitializeTable(memory, size, max_counters, max_threads);

   // We have a valid table, so compute our pointers.

   priv->ComputeMappedPointers(memory);

   return priv.release();

 }

 void StatsTablePrivate::InitializeTable(void* memory, int size,

                                         int max_counters,

                                         int max_threads) {

   // Zero everything.

   memset(memory, 0, size);

   // Initialize the header.

   TableHeader* header = static_cast<TableHeader*>(memory);

   header->version = kTableVersion;

   header->size = size;

   header->max_counters = max_counters;

   header->max_threads = max_threads;

 }

 void StatsTablePrivate::ComputeMappedPointers(void* memory) {

   char* data = static_cast<char*>(memory);

   int offset = 0;

   table_header_ = reinterpret_cast<TableHeader*>(data);

   offset += sizeof(*table_header_);

   offset += AlignOffset(offset);

   // Verify we're looking at a valid StatsTable.

   DCHECK_EQ(table_header_->version, kTableVersion);

   thread_names_table_ = reinterpret_cast<char*>(data + offset);

   offset += sizeof(char) *

             max_threads() * StatsTable::kMaxThreadNameLength;

   offset += AlignOffset(offset);

   thread_tid_table_ = reinterpret_cast<PlatformThreadId*>(data + offset);

   offset += sizeof(int) * max_threads();

   offset += AlignOffset(offset);

   thread_pid_table_ = reinterpret_cast<int*>(data + offset);

   offset += sizeof(int) * max_threads();

   offset += AlignOffset(offset);

   counter_names_table_ = reinterpret_cast<char*>(data + offset);

   offset += sizeof(char) *

             max_counters() * StatsTable::kMaxCounterNameLength;

   offset += AlignOffset(offset);

   data_table_ = reinterpret_cast<int*>(data + offset);

   offset += sizeof(int) * max_threads() * max_counters();

   DCHECK_EQ(offset, size());

 }

 // We keep a singleton table which can be easily accessed.

 StatsTable* StatsTable::global_table_ = NULL;

 StatsTable::StatsTable(const std::string& name, int max_threads,

                        int max_counters)

     : impl_(NULL),

       tls_index_(SlotReturnFunction) {

   int table_size =

     AlignedSize(sizeof(StatsTablePrivate::TableHeader)) +

     AlignedSize((max_counters * sizeof(char) * kMaxCounterNameLength)) +

     AlignedSize((max_threads * sizeof(char) * kMaxThreadNameLength)) +

     AlignedSize(max_threads * sizeof(int)) +

     AlignedSize(max_threads * sizeof(int)) +

     AlignedSize((sizeof(int) * (max_counters * max_threads)));

   impl_ = StatsTablePrivate::New(name, table_size, max_threads, max_counters);

   // TODO(port): clean up this error reporting.

 #if defined(OS_WIN)

   if (!impl_)

     CHROMIUM_LOG(ERROR) << "StatsTable did not initialize:" << GetLastError();

 #elif defined(OS_POSIX)

   if (!impl_)

     CHROMIUM_LOG(ERROR) << "StatsTable did not initialize:" << strerror(errno);

 #endif

 }

 StatsTable::~StatsTable() {

   // Before we tear down our copy of the table, be sure to

   // unregister our thread.

   UnregisterThread();

   // Return ThreadLocalStorage.  At this point, if any registered threads

   // still exist, they cannot Unregister.

   tls_index_.Free();

   // Cleanup our shared memory.

   delete impl_;

   // If we are the global table, unregister ourselves.

   if (global_table_ == this)

     global_table_ = NULL;

 }

 int StatsTable::RegisterThread(const std::string& name) {

   int slot = 0;

   // Registering a thread requires that we lock the shared memory

   // so that two threads don't grab the same slot.  Fortunately,

   // thread creation shouldn't happen in inner loops.

   {

     base::SharedMemoryAutoLock lock(impl_->shared_memory());

     slot = FindEmptyThread();

     if (!slot) {

       return 0;

     }

     DCHECK(impl_);

     // We have space, so consume a column in the table.

     std::string thread_name = name;

     if (name.empty())

       thread_name = kUnknownName;

     base::strlcpy(impl_->thread_name(slot), thread_name.c_str(),

                   kMaxThreadNameLength);

     *(impl_->thread_tid(slot)) = PlatformThread::CurrentId();

     *(impl_->thread_pid(slot)) = base::GetCurrentProcId();

   }

   // Set our thread local storage.

   StatsTableTLSData* data = new StatsTableTLSData;

   data->table = this;

   data->slot = slot;

   tls_index_.Set(data);

   return slot;

 }

 StatsTableTLSData* StatsTable::GetTLSData() const {

   StatsTableTLSData* data =

     static_cast<StatsTableTLSData*>(tls_index_.Get());

   if (!data)

     return NULL;

   DCHECK(data->slot);

   DCHECK_EQ(data->table, this);

   return data;

 }

 void StatsTable::UnregisterThread() {

   UnregisterThread(GetTLSData());

 }

 void StatsTable::UnregisterThread(StatsTableTLSData* data) {

   if (!data)

     return;

   DCHECK(impl_);

   // Mark the slot free by zeroing out the thread name.

   char* name = impl_->thread_name(data->slot);

   *name = '\0';

   // Remove the calling thread's TLS so that it cannot use the slot.

   tls_index_.Set(NULL);

   delete data;

 }

 void StatsTable::SlotReturnFunction(void* data) {

   // This is called by the TLS destructor, which on some platforms has

   // already cleared the TLS info, so use the tls_data argument

   // rather than trying to fetch it ourselves.

   StatsTableTLSData* tls_data = static_cast<StatsTableTLSData*>(data);

   if (tls_data) {

     DCHECK(tls_data->table);

     tls_data->table->UnregisterThread(tls_data);

   }

 }

 int StatsTable::CountThreadsRegistered() const {

   if (!impl_)

     return 0;

   // Loop through the shared memory and count the threads that are active.

   // We intentionally do not lock the table during the operation.

   int count = 0;

   for (int index = 1; index <= impl_->max_threads(); index++) {

     char* name = impl_->thread_name(index);

     if (*name != '\0')

       count++;

   }

   return count;

 }

 int StatsTable::GetSlot() const {

   StatsTableTLSData* data = GetTLSData();

   if (!data)

     return 0;

   return data->slot;

 }

 int StatsTable::FindEmptyThread() const {

   // Note: the API returns slots numbered from 1..N, although

   // internally, the array is 0..N-1.  This is so that we can return

   // zero as "not found".

   //

   // The reason for doing this is because the thread 'slot' is stored

   // in TLS, which is always initialized to zero, not -1.  If 0 were

   // returned as a valid slot number, it would be confused with the

   // uninitialized state.

   if (!impl_)

     return 0;

   int index = 1;

   for (; index <= impl_->max_threads(); index++) {

     char* name = impl_->thread_name(index);

     if (!*name)

       break;

   }

   if (index > impl_->max_threads())

     return 0;  // The table is full.

   return index;

 }

 int StatsTable::FindCounterOrEmptyRow(const std::string& name) const {

   // Note: the API returns slots numbered from 1..N, although

   // internally, the array is 0..N-1.  This is so that we can return

   // zero as "not found".

   //

   // There isn't much reason for this other than to be consistent

   // with the way we track columns for thread slots.  (See comments

   // in FindEmptyThread for why it is done this way).

   if (!impl_)

     return 0;

   int free_slot = 0;

   for (int index = 1; index <= impl_->max_counters(); index++) {

     char* row_name = impl_->counter_name(index);

     if (!*row_name && !free_slot)

       free_slot = index;  // save that we found a free slot

     else if (!strncmp(row_name, name.c_str(), kMaxCounterNameLength))

       return index;

   }

   return free_slot;

 }

 int StatsTable::FindCounter(const std::string& name) {

   // Note: the API returns counters numbered from 1..N, although

   // internally, the array is 0..N-1.  This is so that we can return

   // zero as "not found".

   if (!impl_)

     return 0;

   // Create a scope for our auto-lock.

   {

     AutoLock scoped_lock(counters_lock_);

     // Attempt to find the counter.

     CountersMap::const_iterator iter;

     iter = counters_.find(name);

     if (iter != counters_.end())

       return iter->second;

   }

   // Counter does not exist, so add it.

   return AddCounter(name);

 }

 int StatsTable::AddCounter(const std::string& name) {

   DCHECK(impl_);

   if (!impl_)

     return 0;

   int counter_id = 0;

   {

     // To add a counter to the shared memory, we need the

     // shared memory lock.

     base::SharedMemoryAutoLock lock(impl_->shared_memory());

     // We have space, so create a new counter.

     counter_id = FindCounterOrEmptyRow(name);

     if (!counter_id)

       return 0;

     std::string counter_name = name;

     if (name.empty())

       counter_name = kUnknownName;

     base::strlcpy(impl_->counter_name(counter_id), counter_name.c_str(),

                   kMaxCounterNameLength);

   }

   // now add to our in-memory cache

   {

     AutoLock lock(counters_lock_);

     counters_[name] = counter_id;

   }

   return counter_id;

 }

 int* StatsTable::GetLocation(int counter_id, int slot_id) const {

   if (!impl_)

     return NULL;

   if (slot_id > impl_->max_threads())

     return NULL;

   int* row = impl_->row(counter_id);

   return &(row[slot_id-1]);

 }

 const char* StatsTable::GetRowName(int index) const {

   if (!impl_)

     return NULL;

   return impl_->counter_name(index);

 }

 int StatsTable::GetRowValue(int index, int pid) const {

   if (!impl_)

     return 0;

   int rv = 0;

   int* row = impl_->row(index);

   for (int slot_id = 0; slot_id < impl_->max_threads(); slot_id++) {

     if (pid == 0 || *impl_->thread_pid(slot_id) == pid)

       rv += row[slot_id];

   }

   return rv;

 }

 int StatsTable::GetRowValue(int index) const {

   return GetRowValue(index, 0);

 }

 int StatsTable::GetCounterValue(const std::string& name, int pid) {

   if (!impl_)

     return 0;

   int row = FindCounter(name);

   if (!row)

     return 0;

   return GetRowValue(row, pid);

 }

 int StatsTable::GetCounterValue(const std::string& name) {

   return GetCounterValue(name, 0);

 }

 int StatsTable::GetMaxCounters() const {

   if (!impl_)

     return 0;

   return impl_->max_counters();

 }

 int StatsTable::GetMaxThreads() const {

   if (!impl_)

     return 0;

   return impl_->max_threads();

 }

 int* StatsTable::FindLocation(const char* name) {

   // Get the static StatsTable

   StatsTable *table = StatsTable::current();

   if (!table)

     return NULL;

   // Get the slot for this thread.  Try to register

   // it if none exists.

   int slot = table->GetSlot();

   if (!slot && !(slot = table->RegisterThread("")))

       return NULL;

   // Find the counter id for the counter.

   std::string str_name(name);

   int counter = table->FindCounter(str_name);

   // Now we can find the location in the table.

   return table->GetLocation(counter, slot);

 }