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      1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "base/thread_local_storage.h"
      6 
      7 #include <windows.h>
      8 
      9 #include "base/logging.h"
     10 
     11 // In order to make TLS destructors work, we need to keep function
     12 // pointers to the destructor for each TLS that we allocate.
     13 // We make this work by allocating a single OS-level TLS, which
     14 // contains an array of slots for the application to use.  In
     15 // parallel, we also allocate an array of destructors, which we
     16 // keep track of and call when threads terminate.
     17 
     18 // tls_key_ is the one native TLS that we use.  It stores our
     19 // table.
     20 long ThreadLocalStorage::tls_key_ = TLS_OUT_OF_INDEXES;
     21 
     22 // tls_max_ is the high-water-mark of allocated thread local storage.
     23 // We intentionally skip 0 so that it is not confused with an
     24 // unallocated TLS slot.
     25 long ThreadLocalStorage::tls_max_ = 1;
     26 
     27 // An array of destructor function pointers for the slots.  If
     28 // a slot has a destructor, it will be stored in its corresponding
     29 // entry in this array.
     30 ThreadLocalStorage::TLSDestructorFunc
     31   ThreadLocalStorage::tls_destructors_[kThreadLocalStorageSize];
     32 
     33 void** ThreadLocalStorage::Initialize() {
     34   if (tls_key_ == TLS_OUT_OF_INDEXES) {
     35     long value = TlsAlloc();
     36     DCHECK(value != TLS_OUT_OF_INDEXES);
     37 
     38     // Atomically test-and-set the tls_key.  If the key is TLS_OUT_OF_INDEXES,
     39     // go ahead and set it.  Otherwise, do nothing, as another
     40     // thread already did our dirty work.
     41     if (InterlockedCompareExchange(&tls_key_, value, TLS_OUT_OF_INDEXES) !=
     42             TLS_OUT_OF_INDEXES) {
     43       // We've been shortcut. Another thread replaced tls_key_ first so we need
     44       // to destroy our index and use the one the other thread got first.
     45       TlsFree(value);
     46     }
     47   }
     48   DCHECK(TlsGetValue(tls_key_) == NULL);
     49 
     50   // Create an array to store our data.
     51   void** tls_data = new void*[kThreadLocalStorageSize];
     52   memset(tls_data, 0, sizeof(void*[kThreadLocalStorageSize]));
     53   TlsSetValue(tls_key_, tls_data);
     54   return tls_data;
     55 }
     56 
     57 ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor)
     58     : initialized_(false) {
     59   Initialize(destructor);
     60 }
     61 
     62 bool ThreadLocalStorage::Slot::Initialize(TLSDestructorFunc destructor) {
     63   if (tls_key_ == TLS_OUT_OF_INDEXES || !TlsGetValue(tls_key_))
     64     ThreadLocalStorage::Initialize();
     65 
     66   // Grab a new slot.
     67   slot_ = InterlockedIncrement(&tls_max_) - 1;
     68   if (slot_ >= kThreadLocalStorageSize) {
     69     NOTREACHED();
     70     return false;
     71   }
     72 
     73   // Setup our destructor.
     74   tls_destructors_[slot_] = destructor;
     75   initialized_ = true;
     76   return true;
     77 }
     78 
     79 void ThreadLocalStorage::Slot::Free() {
     80   // At this time, we don't reclaim old indices for TLS slots.
     81   // So all we need to do is wipe the destructor.
     82   tls_destructors_[slot_] = NULL;
     83   initialized_ = false;
     84 }
     85 
     86 void* ThreadLocalStorage::Slot::Get() const {
     87   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
     88   if (!tls_data)
     89     tls_data = ThreadLocalStorage::Initialize();
     90   DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);
     91   return tls_data[slot_];
     92 }
     93 
     94 void ThreadLocalStorage::Slot::Set(void* value) {
     95   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
     96   if (!tls_data)
     97     tls_data = ThreadLocalStorage::Initialize();
     98   DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);
     99   tls_data[slot_] = value;
    100 }
    101 
    102 void ThreadLocalStorage::ThreadExit() {
    103   if (tls_key_ == TLS_OUT_OF_INDEXES)
    104     return;
    105 
    106   void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
    107 
    108   // Maybe we have never initialized TLS for this thread.
    109   if (!tls_data)
    110     return;
    111 
    112   for (int slot = 0; slot < tls_max_; slot++) {
    113     if (tls_destructors_[slot] != NULL) {
    114       void* value = tls_data[slot];
    115       tls_destructors_[slot](value);
    116     }
    117   }
    118 
    119   delete[] tls_data;
    120 
    121   // In case there are other "onexit" handlers...
    122   TlsSetValue(tls_key_, NULL);
    123 }
    124 
    125 // Thread Termination Callbacks.
    126 // Windows doesn't support a per-thread destructor with its
    127 // TLS primitives.  So, we build it manually by inserting a
    128 // function to be called on each thread's exit.
    129 // This magic is from http://www.codeproject.com/threads/tls.asp
    130 // and it works for VC++ 7.0 and later.
    131 
    132 #ifdef _WIN64
    133 
    134 // This makes the linker create the TLS directory if it's not already
    135 // there.  (e.g. if __declspec(thread) is not used).
    136 #pragma comment(linker, "/INCLUDE:_tls_used")
    137 
    138 #else  // _WIN64
    139 
    140 // This makes the linker create the TLS directory if it's not already
    141 // there.  (e.g. if __declspec(thread) is not used).
    142 #pragma comment(linker, "/INCLUDE:__tls_used")
    143 
    144 #endif  // _WIN64
    145 
    146 // Static callback function to call with each thread termination.
    147 void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved)
    148 {
    149   // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+
    150   // and on W2K and W2K3. So don't assume it is sent.
    151   if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason)
    152     ThreadLocalStorage::ThreadExit();
    153 }
    154 
    155 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are
    156 // called automatically by the OS loader code (not the CRT) when the module is
    157 // loaded and on thread creation. They are NOT called if the module has been
    158 // loaded by a LoadLibrary() call. It must have implicitly been loaded at
    159 // process startup.
    160 // By implicitly loaded, I mean that it is directly referenced by the main EXE
    161 // or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being
    162 // implicitly loaded.
    163 //
    164 // See VC\crt\src\tlssup.c for reference.
    165 #ifdef _WIN64
    166 
    167 // .CRT section is merged with .rdata on x64 so it must be constant data.
    168 #pragma const_seg(".CRT$XLB")
    169 // When defining a const variable, it must have external linkage to be sure the
    170 // linker doesn't discard it. If this value is discarded, the OnThreadExit
    171 // function will never be called.
    172 extern const PIMAGE_TLS_CALLBACK p_thread_callback;
    173 const PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit;
    174 
    175 // Reset the default section.
    176 #pragma const_seg()
    177 
    178 #else  // _WIN64
    179 
    180 #pragma data_seg(".CRT$XLB")
    181 PIMAGE_TLS_CALLBACK p_thread_callback = OnThreadExit;
    182 
    183 // Reset the default section.
    184 #pragma data_seg()
    185 
    186 #endif  // _WIN64
    187