1// Copyright (c) 2011 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/threading/thread_local_storage.h"
6
7#include <windows.h>
8
9#include "base/logging.h"
10
11namespace base {
12
13// In order to make TLS destructors work, we need to keep function
14// pointers to the destructor for each TLS that we allocate.
15// We make this work by allocating a single OS-level TLS, which
16// contains an array of slots for the application to use.  In
17// parallel, we also allocate an array of destructors, which we
18// keep track of and call when threads terminate.
19
20// tls_key_ is the one native TLS that we use.  It stores our
21// table.
22long ThreadLocalStorage::tls_key_ = TLS_OUT_OF_INDEXES;
23
24// tls_max_ is the high-water-mark of allocated thread local storage.
25// We intentionally skip 0 so that it is not confused with an
26// unallocated TLS slot.
27long ThreadLocalStorage::tls_max_ = 1;
28
29// An array of destructor function pointers for the slots.  If
30// a slot has a destructor, it will be stored in its corresponding
31// entry in this array.
32ThreadLocalStorage::TLSDestructorFunc
33  ThreadLocalStorage::tls_destructors_[kThreadLocalStorageSize];
34
35void** ThreadLocalStorage::Initialize() {
36  if (tls_key_ == TLS_OUT_OF_INDEXES) {
37    long value = TlsAlloc();
38    DCHECK(value != TLS_OUT_OF_INDEXES);
39
40    // Atomically test-and-set the tls_key.  If the key is TLS_OUT_OF_INDEXES,
41    // go ahead and set it.  Otherwise, do nothing, as another
42    // thread already did our dirty work.
43    if (InterlockedCompareExchange(&tls_key_, value, TLS_OUT_OF_INDEXES) !=
44            TLS_OUT_OF_INDEXES) {
45      // We've been shortcut. Another thread replaced tls_key_ first so we need
46      // to destroy our index and use the one the other thread got first.
47      TlsFree(value);
48    }
49  }
50  DCHECK(!TlsGetValue(tls_key_));
51
52  // Create an array to store our data.
53  void** tls_data = new void*[kThreadLocalStorageSize];
54  memset(tls_data, 0, sizeof(void*[kThreadLocalStorageSize]));
55  TlsSetValue(tls_key_, tls_data);
56  return tls_data;
57}
58
59ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor)
60    : initialized_(false),
61      slot_(0) {
62  Initialize(destructor);
63}
64
65bool ThreadLocalStorage::Slot::Initialize(TLSDestructorFunc destructor) {
66  if (tls_key_ == TLS_OUT_OF_INDEXES || !TlsGetValue(tls_key_))
67    ThreadLocalStorage::Initialize();
68
69  // Grab a new slot.
70  slot_ = InterlockedIncrement(&tls_max_) - 1;
71  if (slot_ >= kThreadLocalStorageSize) {
72    NOTREACHED();
73    return false;
74  }
75
76  // Setup our destructor.
77  tls_destructors_[slot_] = destructor;
78  initialized_ = true;
79  return true;
80}
81
82void ThreadLocalStorage::Slot::Free() {
83  // At this time, we don't reclaim old indices for TLS slots.
84  // So all we need to do is wipe the destructor.
85  tls_destructors_[slot_] = NULL;
86  initialized_ = false;
87}
88
89void* ThreadLocalStorage::Slot::Get() const {
90  void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
91  if (!tls_data)
92    tls_data = ThreadLocalStorage::Initialize();
93  DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);
94  return tls_data[slot_];
95}
96
97void ThreadLocalStorage::Slot::Set(void* value) {
98  void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
99  if (!tls_data)
100    tls_data = ThreadLocalStorage::Initialize();
101  DCHECK(slot_ >= 0 && slot_ < kThreadLocalStorageSize);
102  tls_data[slot_] = value;
103}
104
105void ThreadLocalStorage::ThreadExit() {
106  if (tls_key_ == TLS_OUT_OF_INDEXES)
107    return;
108
109  void** tls_data = static_cast<void**>(TlsGetValue(tls_key_));
110
111  // Maybe we have never initialized TLS for this thread.
112  if (!tls_data)
113    return;
114
115  for (int slot = 0; slot < tls_max_; slot++) {
116    if (tls_destructors_[slot] != NULL) {
117      void* value = tls_data[slot];
118      tls_destructors_[slot](value);
119    }
120  }
121
122  delete[] tls_data;
123
124  // In case there are other "onexit" handlers...
125  TlsSetValue(tls_key_, NULL);
126}
127
128}  // namespace base
129
130// Thread Termination Callbacks.
131// Windows doesn't support a per-thread destructor with its
132// TLS primitives.  So, we build it manually by inserting a
133// function to be called on each thread's exit.
134// This magic is from http://www.codeproject.com/threads/tls.asp
135// and it works for VC++ 7.0 and later.
136
137// Force a reference to _tls_used to make the linker create the TLS directory
138// if it's not already there.  (e.g. if __declspec(thread) is not used).
139// Force a reference to p_thread_callback_base to prevent whole program
140// optimization from discarding the variable.
141#ifdef _WIN64
142
143#pragma comment(linker, "/INCLUDE:_tls_used")
144#pragma comment(linker, "/INCLUDE:p_thread_callback_base")
145
146#else  // _WIN64
147
148#pragma comment(linker, "/INCLUDE:__tls_used")
149#pragma comment(linker, "/INCLUDE:_p_thread_callback_base")
150
151#endif  // _WIN64
152
153// Static callback function to call with each thread termination.
154void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved) {
155  // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+
156  // and on W2K and W2K3. So don't assume it is sent.
157  if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason)
158    base::ThreadLocalStorage::ThreadExit();
159}
160
161// .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are
162// called automatically by the OS loader code (not the CRT) when the module is
163// loaded and on thread creation. They are NOT called if the module has been
164// loaded by a LoadLibrary() call. It must have implicitly been loaded at
165// process startup.
166// By implicitly loaded, I mean that it is directly referenced by the main EXE
167// or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being
168// implicitly loaded.
169//
170// See VC\crt\src\tlssup.c for reference.
171
172// extern "C" suppresses C++ name mangling so we know the symbol name for the
173// linker /INCLUDE:symbol pragma above.
174extern "C" {
175// The linker must not discard p_thread_callback_base.  (We force a reference
176// to this variable with a linker /INCLUDE:symbol pragma to ensure that.) If
177// this variable is discarded, the OnThreadExit function will never be called.
178#ifdef _WIN64
179
180// .CRT section is merged with .rdata on x64 so it must be constant data.
181#pragma const_seg(".CRT$XLB")
182// When defining a const variable, it must have external linkage to be sure the
183// linker doesn't discard it.
184extern const PIMAGE_TLS_CALLBACK p_thread_callback_base;
185const PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
186
187// Reset the default section.
188#pragma const_seg()
189
190#else  // _WIN64
191
192#pragma data_seg(".CRT$XLB")
193PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
194
195// Reset the default section.
196#pragma data_seg()
197
198#endif  // _WIN64
199}  // extern "C"
200