Revert 241657 "Implement chromium's TLS."

Caused intermittent browser process crashes on Linux Debug configurations.
See Issue 329747 for details.

BUG=329747,264406

> Implement chromium's TLS.
> 
> Using one system TLS to implement multiple chrome's TLS slots.
> 
> BUG=264406
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=241144
> 
> Review URL: https://codereview.chromium.org/60743004

TBR=michaelbai@chromium.org

Review URL: https://codereview.chromium.org/121393002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242549 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 223 insertions, 343 deletions

diff --git a/base/threading/thread_local_storage.cc b/base/threading/thread_local_storage.cc
deleted file mode 100644
index e5a3cd9..0000000
--- a/base/threading/thread_local_storage.cc
+++ /dev/null
@@ -1,250 +0,0 @@
-// Copyright 2013 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/threading/thread_local_storage.h"
-
-#include "base/atomicops.h"
-#include "base/logging.h"
-
-using base::internal::PlatformThreadLocalStorage;
-
-namespace {
-// In order to make TLS destructors work, we need to keep around a function
-// pointer to the destructor for each slot. We keep this array of pointers in a
-// global (static) array.
-// We use the single OS-level TLS slot (giving us one pointer per thread) to
-// hold a pointer to a per-thread array (table) of slots that we allocate to
-// Chromium consumers.
-
-// g_native_tls_key is the one native TLS that we use.  It stores our table.
-base::subtle::AtomicWord g_native_tls_key =
-    PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES;
-
-// g_last_used_tls_key is the high-water-mark of allocated thread local storage.
-// Each allocation is an index into our g_tls_destructors[].  Each such index is
-// assigned to the instance variable slot_ in a ThreadLocalStorage::Slot
-// instance.  We reserve the value slot_ == 0 to indicate that the corresponding
-// instance of ThreadLocalStorage::Slot has been freed (i.e., destructor called,
-// etc.).  This reserved use of 0 is then stated as the initial value of
-// g_last_used_tls_key, so that the first issued index will be 1.
-base::subtle::Atomic32 g_last_used_tls_key = 0;
-
-// The maximum number of 'slots' in our thread local storage stack.
-const int kThreadLocalStorageSize = 64;
-
-// The maximum number of times to try to clear slots by calling destructors.
-// Use pthread naming convention for clarity.
-const int kMaxDestructorIterations = kThreadLocalStorageSize;
-
-// An array of destructor function pointers for the slots.  If a slot has a
-// destructor, it will be stored in its corresponding entry in this array.
-// The elements are volatile to ensure that when the compiler reads the value
-// to potentially call the destructor, it does so once, and that value is tested
-// for null-ness and then used. Yes, that would be a weird de-optimization,
-// but I can imagine some register machines where it was just as easy to
-// re-fetch an array element, and I want to be sure a call to free the key
-// (i.e., null out the destructor entry) that happens on a separate thread can't
-// hurt the racy calls to the destructors on another thread.
-volatile base::ThreadLocalStorage::TLSDestructorFunc
-    g_tls_destructors[kThreadLocalStorageSize];
-
-// This function is called to initialize our entire Chromium TLS system.
-// It may be called very early, and we need to complete most all of the setup
-// (initialization) before calling *any* memory allocator functions, which may
-// recursively depend on this initialization.
-// As a result, we use Atomics, and avoid anything (like a singleton) that might
-// require memory allocations.
-void** ConstructTlsVector() {
-  PlatformThreadLocalStorage::TLSKey key =
-      base::subtle::NoBarrier_Load(&g_native_tls_key);
-  if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES) {
-    CHECK(PlatformThreadLocalStorage::AllocTLS(&key));
-
-    // The TLS_KEY_OUT_OF_INDEXES is used to find out whether the key is set or
-    // not in NoBarrier_CompareAndSwap, but Posix doesn't have invalid key, we
-    // define an almost impossible value be it.
-    // If we really get TLS_KEY_OUT_OF_INDEXES as value of key, just alloc
-    // another TLS slot.
-    if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES) {
-      PlatformThreadLocalStorage::TLSKey tmp = key;
-      CHECK(PlatformThreadLocalStorage::AllocTLS(&key) &&
-            key != PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES);
-      PlatformThreadLocalStorage::FreeTLS(tmp);
-    }
-    // Atomically test-and-set the tls_key.  If the key is
-    // TLS_KEY_OUT_OF_INDEXES, go ahead and set it.  Otherwise, do nothing, as
-    // another thread already did our dirty work.
-    if (PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES !=
-        base::subtle::NoBarrier_CompareAndSwap(&g_native_tls_key,
-            PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES, key)) {
-      // We've been shortcut. Another thread replaced g_native_tls_key first so
-      // we need to destroy our index and use the one the other thread got
-      // first.
-      PlatformThreadLocalStorage::FreeTLS(key);
-      key = base::subtle::NoBarrier_Load(&g_native_tls_key);
-    }
-  }
-  CHECK(!PlatformThreadLocalStorage::GetTLSValue(key));
-
-  // Some allocators, such as TCMalloc, make use of thread local storage.
-  // As a result, any attempt to call new (or malloc) will lazily cause such a
-  // system to initialize, which will include registering for a TLS key.  If we
-  // are not careful here, then that request to create a key will call new back,
-  // and we'll have an infinite loop.  We avoid that as follows:
-  // Use a stack allocated vector, so that we don't have dependence on our
-  // allocator until our service is in place.  (i.e., don't even call new until
-  // after we're setup)
-  void* stack_allocated_tls_data[kThreadLocalStorageSize];
-  memset(stack_allocated_tls_data, 0, sizeof(stack_allocated_tls_data));
-  // Ensure that any rentrant calls change the temp version.
-  PlatformThreadLocalStorage::SetTLSValue(key, stack_allocated_tls_data);
-
-  // Allocate an array to store our data.
-  void** tls_data = new void*[kThreadLocalStorageSize];
-  memcpy(tls_data, stack_allocated_tls_data, sizeof(stack_allocated_tls_data));
-  PlatformThreadLocalStorage::SetTLSValue(key, tls_data);
-  return tls_data;
-}
-
-void OnThreadExitInternal(void* value) {
-  DCHECK(value);
-  void** tls_data = static_cast<void**>(value);
-  // Some allocators, such as TCMalloc, use TLS.  As a result, when a thread
-  // terminates, one of the destructor calls we make may be to shut down an
-  // allocator.  We have to be careful that after we've shutdown all of the
-  // known destructors (perchance including an allocator), that we don't call
-  // the allocator and cause it to resurrect itself (with no possibly destructor
-  // call to follow).  We handle this problem as follows:
-  // Switch to using a stack allocated vector, so that we don't have dependence
-  // on our allocator after we have called all g_tls_destructors.  (i.e., don't
-  // even call delete[] after we're done with destructors.)
-  void* stack_allocated_tls_data[kThreadLocalStorageSize];
-  memcpy(stack_allocated_tls_data, tls_data, sizeof(stack_allocated_tls_data));
-  // Ensure that any re-entrant calls change the temp version.
-  PlatformThreadLocalStorage::TLSKey key =
-      base::subtle::NoBarrier_Load(&g_native_tls_key);
-  PlatformThreadLocalStorage::SetTLSValue(key, stack_allocated_tls_data);
-  delete[] tls_data;  // Our last dependence on an allocator.
-
-  int remaining_attempts = kMaxDestructorIterations;
-  bool need_to_scan_destructors = true;
-  while (need_to_scan_destructors) {
-    need_to_scan_destructors = false;
-    // Try to destroy the first-created-slot (which is slot 1) in our last
-    // destructor call.  That user was able to function, and define a slot with
-    // no other services running, so perhaps it is a basic service (like an
-    // allocator) and should also be destroyed last.  If we get the order wrong,
-    // then we'll itterate several more times, so it is really not that
-    // critical (but it might help).
-    base::subtle::Atomic32 last_used_tls_key =
-        base::subtle::NoBarrier_Load(&g_last_used_tls_key);
-    for (int slot = last_used_tls_key; slot > 0; --slot) {
-      void* value = stack_allocated_tls_data[slot];
-      if (value == NULL)
-        continue;
-
-      base::ThreadLocalStorage::TLSDestructorFunc destructor =
-          g_tls_destructors[slot];
-      if (destructor == NULL)
-        continue;
-      stack_allocated_tls_data[slot] = NULL;  // pre-clear the slot.
-      destructor(value);
-      // Any destructor might have called a different service, which then set
-      // a different slot to a non-NULL value.  Hence we need to check
-      // the whole vector again.  This is a pthread standard.
-      need_to_scan_destructors = true;
-    }
-    if (--remaining_attempts <= 0) {
-      NOTREACHED();  // Destructors might not have been called.
-      break;
-    }
-  }
-
-  // Remove our stack allocated vector.
-  PlatformThreadLocalStorage::SetTLSValue(key, NULL);
-}
-
-}  // namespace
-
-namespace base {
-
-namespace internal {
-
-#if defined(OS_WIN)
-void PlatformThreadLocalStorage::OnThreadExit() {
-  PlatformThreadLocalStorage::TLSKey key =
-      base::subtle::NoBarrier_Load(&g_native_tls_key);
-  if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES)
-    return;
-  void *tls_data = GetTLSValue(key);
-  // Maybe we have never initialized TLS for this thread.
-  if (!tls_data)
-    return;
-  OnThreadExitInternal(tls_data);
-}
-#elif defined(OS_POSIX)
-void PlatformThreadLocalStorage::OnThreadExit(void* value) {
-  OnThreadExitInternal(value);
-}
-#endif  // defined(OS_WIN)
-
-}  // namespace internal
-
-ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
-  initialized_ = false;
-  slot_ = 0;
-  Initialize(destructor);
-}
-
-bool ThreadLocalStorage::StaticSlot::Initialize(TLSDestructorFunc destructor) {
-  PlatformThreadLocalStorage::TLSKey key =
-      base::subtle::NoBarrier_Load(&g_native_tls_key);
-  if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES ||
-      !PlatformThreadLocalStorage::GetTLSValue(key))
-    ConstructTlsVector();
-
-  // Grab a new slot.
-  slot_ = base::subtle::NoBarrier_AtomicIncrement(&g_last_used_tls_key, 1);
-  DCHECK_GT(slot_, 0);
-  CHECK_LT(slot_, kThreadLocalStorageSize);
-
-  // Setup our destructor.
-  g_tls_destructors[slot_] = destructor;
-  initialized_ = true;
-  return true;
-}
-
-void ThreadLocalStorage::StaticSlot::Free() {
-  // At this time, we don't reclaim old indices for TLS slots.
-  // So all we need to do is wipe the destructor.
-  DCHECK_GT(slot_, 0);
-  DCHECK_LT(slot_, kThreadLocalStorageSize);
-  g_tls_destructors[slot_] = NULL;
-  slot_ = 0;
-  initialized_ = false;
-}
-
-void* ThreadLocalStorage::StaticSlot::Get() const {
-  void** tls_data = static_cast<void**>(
-      PlatformThreadLocalStorage::GetTLSValue(
-          base::subtle::NoBarrier_Load(&g_native_tls_key)));
-  if (!tls_data)
-    tls_data = ConstructTlsVector();
-  DCHECK_GT(slot_, 0);
-  DCHECK_LT(slot_, kThreadLocalStorageSize);
-  return tls_data[slot_];
-}
-
-void ThreadLocalStorage::StaticSlot::Set(void* value) {
-  void** tls_data = static_cast<void**>(
-      PlatformThreadLocalStorage::GetTLSValue(
-          base::subtle::NoBarrier_Load(&g_native_tls_key)));
-  if (!tls_data)
-    tls_data = ConstructTlsVector();
-  DCHECK_GT(slot_, 0);
-  DCHECK_LT(slot_, kThreadLocalStorageSize);
-  tls_data[slot_] = value;
-}
-
-}  // namespace base
diff --git a/base/threading/thread_local_storage.h b/base/threading/thread_local_storage.h
index 53ebe55..eb5648f 100644
--- a/base/threading/thread_local_storage.h
+++ b/base/threading/thread_local_storage.h
@@ -8,71 +8,12 @@
 #include "base/base_export.h"
 #include "base/basictypes.h"
 
-#if defined(OS_WIN)
-#include <windows.h>
-#elif defined(OS_POSIX)
+#if defined(OS_POSIX)
 #include <pthread.h>
 #endif
 
 namespace base {
 
-namespace internal {
-
-// WARNING: You should *NOT* be using this class directly.
-// PlatformThreadLocalStorage is low-level abstraction to the OS's TLS
-// interface, you should instead be using ThreadLocalStorage::StaticSlot/Slot.
-class BASE_EXPORT PlatformThreadLocalStorage {
- public:
-
-#if defined(OS_WIN)
-  typedef unsigned long TLSKey;
-  enum { TLS_KEY_OUT_OF_INDEXES = TLS_OUT_OF_INDEXES };
-#elif defined(OS_POSIX)
-  typedef pthread_key_t TLSKey;
-  // The following is a "reserved key" which is used in our generic Chromium
-  // ThreadLocalStorage implementation.  We expect that an OS will not return
-  // such a key, but if it is returned (i.e., the OS tries to allocate it) we
-  // will just request another key.
-  enum { TLS_KEY_OUT_OF_INDEXES = 0x7FFFFFFF };
-#endif
-
-  // The following methods need to be supported on each OS platform, so that
-  // the Chromium ThreadLocalStore functionality can be constructed.
-  // Chromium will use these methods to acquire a single OS slot, and then use
-  // that to support a much larger number of Chromium slots (independent of the
-  // OS restrictions).
-  // The following returns true if it successfully is able to return an OS
-  // key in |key|.
-  static bool AllocTLS(TLSKey* key);
-  // Note: FreeTLS() doesn't have to be called, it is fine with this leak, OS
-  // might not reuse released slot, you might just reset the TLS value with
-  // SetTLSValue().
-  static void FreeTLS(TLSKey key);
-  static void SetTLSValue(TLSKey key, void* value);
-  static void* GetTLSValue(TLSKey key);
-
-  // Each platform (OS implementation) is required to call this method on each
-  // terminating thread when the thread is about to terminate.  This method
-  // will then call all registered destructors for slots in Chromium
-  // ThreadLocalStorage, until there are no slot values remaining as having
-  // been set on this thread.
-  // Destructors may end up being called multiple times on a terminating
-  // thread, as other destructors may re-set slots that were previously
-  // destroyed.
-#if defined(OS_WIN)
-  // Since Windows which doesn't support TLS destructor, the implementation
-  // should use GetTLSValue() to retrieve the value of TLS slot.
-  static void OnThreadExit();
-#elif defined(OS_POSIX)
-  // |Value| is the data stored in TLS slot, The implementation can't use
-  // GetTLSValue() to retrieve the value of slot as it has already been reset
-  // in Posix.
-  static void OnThreadExit(void* value);
-#endif
-};
-
-}  // namespace internal
-
 // Wrapper for thread local storage.  This class doesn't do much except provide
 // an API for portability.
 class BASE_EXPORT ThreadLocalStorage {
@@ -119,7 +60,12 @@ class BASE_EXPORT ThreadLocalStorage {
 
     // The internals of this struct should be considered private.
     bool initialized_;
+#if defined(OS_WIN)
     int slot_;
+#elif defined(OS_POSIX)
+    pthread_key_t key_;
+#endif
+
   };
 
   // A convenience wrapper around StaticSlot with a constructor. Can be used
@@ -131,8 +77,11 @@ class BASE_EXPORT ThreadLocalStorage {
 
    private:
     using StaticSlot::initialized_;
+#if defined(OS_WIN)
     using StaticSlot::slot_;
-
+#elif defined(OS_POSIX)
+    using StaticSlot::key_;
+#endif
     DISALLOW_COPY_AND_ASSIGN(Slot);
   };
 
diff --git a/base/threading/thread_local_storage_posix.cc b/base/threading/thread_local_storage_posix.cc
index ebaf400..75da5a7 100644
--- a/base/threading/thread_local_storage_posix.cc
+++ b/base/threading/thread_local_storage_posix.cc
@@ -8,27 +8,42 @@
 
 namespace base {
 
-namespace internal {
-
-bool PlatformThreadLocalStorage::AllocTLS(TLSKey* key) {
-  return !pthread_key_create(key,
-      base::internal::PlatformThreadLocalStorage::OnThreadExit);
+ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
+  initialized_ = false;
+  key_ = 0;
+  Initialize(destructor);
 }
 
-void PlatformThreadLocalStorage::FreeTLS(TLSKey key) {
-  int ret = pthread_key_delete(key);
-  DCHECK_EQ(ret, 0);
+bool ThreadLocalStorage::StaticSlot::Initialize(TLSDestructorFunc destructor) {
+  DCHECK(!initialized_);
+  int error = pthread_key_create(&key_, destructor);
+  if (error) {
+    NOTREACHED();
+    return false;
+  }
+
+  initialized_ = true;
+  return true;
 }
 
-void* PlatformThreadLocalStorage::GetTLSValue(TLSKey key) {
-  return pthread_getspecific(key);
+void ThreadLocalStorage::StaticSlot::Free() {
+  DCHECK(initialized_);
+  int error = pthread_key_delete(key_);
+  if (error)
+    NOTREACHED();
+  initialized_ = false;
 }
 
-void PlatformThreadLocalStorage::SetTLSValue(TLSKey key, void* value) {
-  int ret = pthread_setspecific(key, value);
-  DCHECK_EQ(ret, 0);
+void* ThreadLocalStorage::StaticSlot::Get() const {
+  DCHECK(initialized_);
+  return pthread_getspecific(key_);
 }
 
-}  // namespace internal
+void ThreadLocalStorage::StaticSlot::Set(void* value) {
+  DCHECK(initialized_);
+  int error = pthread_setspecific(key_, value);
+  if (error)
+    NOTREACHED();
+}
 
 }  // namespace base
diff --git a/base/threading/thread_local_storage_win.cc b/base/threading/thread_local_storage_win.cc
index 42a7d01..0ae3cb4 100644
--- a/base/threading/thread_local_storage_win.cc
+++ b/base/threading/thread_local_storage_win.cc
@@ -8,34 +8,200 @@
 
 #include "base/logging.h"
 
-namespace base {
 
-namespace internal {
+namespace {
+// In order to make TLS destructors work, we need to keep function
+// pointers to the destructor for each TLS that we allocate.
+// We make this work by allocating a single OS-level TLS, which
+// contains an array of slots for the application to use.  In
+// parallel, we also allocate an array of destructors, which we
+// keep track of and call when threads terminate.
+
+// g_native_tls_key is the one native TLS that we use.  It stores our table.
+long g_native_tls_key = TLS_OUT_OF_INDEXES;
+
+// g_last_used_tls_key is the high-water-mark of allocated thread local storage.
+// Each allocation is an index into our g_tls_destructors[].  Each such index is
+// assigned to the instance variable slot_ in a ThreadLocalStorage::Slot
+// instance.  We reserve the value slot_ == 0 to indicate that the corresponding
+// instance of ThreadLocalStorage::Slot has been freed (i.e., destructor called,
+// etc.).  This reserved use of 0 is then stated as the initial value of
+// g_last_used_tls_key, so that the first issued index will be 1.
+long g_last_used_tls_key = 0;
+
+// The maximum number of 'slots' in our thread local storage stack.
+const int kThreadLocalStorageSize = 64;
+
+// The maximum number of times to try to clear slots by calling destructors.
+// Use pthread naming convention for clarity.
+const int kMaxDestructorIterations = kThreadLocalStorageSize;
+
+// An array of destructor function pointers for the slots.  If a slot has a
+// destructor, it will be stored in its corresponding entry in this array.
+// The elements are volatile to ensure that when the compiler reads the value
+// to potentially call the destructor, it does so once, and that value is tested
+// for null-ness and then used. Yes, that would be a weird de-optimization,
+// but I can imagine some register machines where it was just as easy to
+// re-fetch an array element, and I want to be sure a call to free the key
+// (i.e., null out the destructor entry) that happens on a separate thread can't
+// hurt the racy calls to the destructors on another thread.
+volatile base::ThreadLocalStorage::TLSDestructorFunc
+    g_tls_destructors[kThreadLocalStorageSize];
+
+void** ConstructTlsVector() {
+  if (g_native_tls_key == TLS_OUT_OF_INDEXES) {
+    long value = TlsAlloc();
+    DCHECK(value != TLS_OUT_OF_INDEXES);
 
-bool PlatformThreadLocalStorage::AllocTLS(TLSKey* key) {
-  TLSKey value = TlsAlloc();
-  if (value != TLS_OUT_OF_INDEXES) {
-    *key = value;
-    return true;
+    // Atomically test-and-set the tls_key.  If the key is TLS_OUT_OF_INDEXES,
+    // go ahead and set it.  Otherwise, do nothing, as another
+    // thread already did our dirty work.
+    if (TLS_OUT_OF_INDEXES != InterlockedCompareExchange(
+            &g_native_tls_key, value, TLS_OUT_OF_INDEXES)) {
+      // We've been shortcut. Another thread replaced g_native_tls_key first so
+      // we need to destroy our index and use the one the other thread got
+      // first.
+      TlsFree(value);
+    }
   }
-  return false;
+  DCHECK(!TlsGetValue(g_native_tls_key));
+
+  // Some allocators, such as TCMalloc, make use of thread local storage.
+  // As a result, any attempt to call new (or malloc) will lazily cause such a
+  // system to initialize, which will include registering for a TLS key.  If we
+  // are not careful here, then that request to create a key will call new back,
+  // and we'll have an infinite loop.  We avoid that as follows:
+  // Use a stack allocated vector, so that we don't have dependence on our
+  // allocator until our service is in place.  (i.e., don't even call new until
+  // after we're setup)
+  void* stack_allocated_tls_data[kThreadLocalStorageSize];
+  memset(stack_allocated_tls_data, 0, sizeof(stack_allocated_tls_data));
+  // Ensure that any rentrant calls change the temp version.
+  TlsSetValue(g_native_tls_key, stack_allocated_tls_data);
+
+  // Allocate an array to store our data.
+  void** tls_data = new void*[kThreadLocalStorageSize];
+  memcpy(tls_data, stack_allocated_tls_data, sizeof(stack_allocated_tls_data));
+  TlsSetValue(g_native_tls_key, tls_data);
+  return tls_data;
 }
 
-void PlatformThreadLocalStorage::FreeTLS(TLSKey key) {
-  BOOL ret = TlsFree(key);
-  DCHECK(ret);
+// Called when we terminate a thread, this function calls any TLS destructors
+// that are pending for this thread.
+void WinThreadExit() {
+  if (g_native_tls_key == TLS_OUT_OF_INDEXES)
+    return;
+
+  void** tls_data = static_cast<void**>(TlsGetValue(g_native_tls_key));
+  // Maybe we have never initialized TLS for this thread.
+  if (!tls_data)
+    return;
+
+  // Some allocators, such as TCMalloc, use TLS.  As a result, when a thread
+  // terminates, one of the destructor calls we make may be to shut down an
+  // allocator.  We have to be careful that after we've shutdown all of the
+  // known destructors (perchance including an allocator), that we don't call
+  // the allocator and cause it to resurrect itself (with no possibly destructor
+  // call to follow).  We handle this problem as follows:
+  // Switch to using a stack allocated vector, so that we don't have dependence
+  // on our allocator after we have called all g_tls_destructors.  (i.e., don't
+  // even call delete[] after we're done with destructors.)
+  void* stack_allocated_tls_data[kThreadLocalStorageSize];
+  memcpy(stack_allocated_tls_data, tls_data, sizeof(stack_allocated_tls_data));
+  // Ensure that any re-entrant calls change the temp version.
+  TlsSetValue(g_native_tls_key, stack_allocated_tls_data);
+  delete[] tls_data;  // Our last dependence on an allocator.
+
+  int remaining_attempts = kMaxDestructorIterations;
+  bool need_to_scan_destructors = true;
+  while (need_to_scan_destructors) {
+    need_to_scan_destructors = false;
+    // Try to destroy the first-created-slot (which is slot 1) in our last
+    // destructor call.  That user was able to function, and define a slot with
+    // no other services running, so perhaps it is a basic service (like an
+    // allocator) and should also be destroyed last.  If we get the order wrong,
+    // then we'll itterate several more times, so it is really not that
+    // critical (but it might help).
+    for (int slot = g_last_used_tls_key; slot > 0; --slot) {
+      void* value = stack_allocated_tls_data[slot];
+      if (value == NULL)
+        continue;
+      base::ThreadLocalStorage::TLSDestructorFunc destructor =
+          g_tls_destructors[slot];
+      if (destructor == NULL)
+        continue;
+      stack_allocated_tls_data[slot] = NULL;  // pre-clear the slot.
+      destructor(value);
+      // Any destructor might have called a different service, which then set
+      // a different slot to a non-NULL value.  Hence we need to check
+      // the whole vector again.  This is a pthread standard.
+      need_to_scan_destructors = true;
+    }
+    if (--remaining_attempts <= 0) {
+      NOTREACHED();  // Destructors might not have been called.
+      break;
+    }
+  }
+
+  // Remove our stack allocated vector.
+  TlsSetValue(g_native_tls_key, NULL);
+}
+
+}  // namespace
+
+namespace base {
+
+ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
+  initialized_ = false;
+  slot_ = 0;
+  Initialize(destructor);
 }
 
-void* PlatformThreadLocalStorage::GetTLSValue(TLSKey key) {
-  return TlsGetValue(key);
+bool ThreadLocalStorage::StaticSlot::Initialize(TLSDestructorFunc destructor) {
+  if (g_native_tls_key == TLS_OUT_OF_INDEXES || !TlsGetValue(g_native_tls_key))
+    ConstructTlsVector();
+
+  // Grab a new slot.
+  slot_ = InterlockedIncrement(&g_last_used_tls_key);
+  DCHECK_GT(slot_, 0);
+  if (slot_ >= kThreadLocalStorageSize) {
+    NOTREACHED();
+    return false;
+  }
+
+  // Setup our destructor.
+  g_tls_destructors[slot_] = destructor;
+  initialized_ = true;
+  return true;
 }
 
-void PlatformThreadLocalStorage::SetTLSValue(TLSKey key, void* value) {
-  BOOL ret = TlsSetValue(key, value);
-  DCHECK(ret);
+void ThreadLocalStorage::StaticSlot::Free() {
+  // At this time, we don't reclaim old indices for TLS slots.
+  // So all we need to do is wipe the destructor.
+  DCHECK_GT(slot_, 0);
+  DCHECK_LT(slot_, kThreadLocalStorageSize);
+  g_tls_destructors[slot_] = NULL;
+  slot_ = 0;
+  initialized_ = false;
 }
 
-}  // namespace internal
+void* ThreadLocalStorage::StaticSlot::Get() const {
+  void** tls_data = static_cast<void**>(TlsGetValue(g_native_tls_key));
+  if (!tls_data)
+    tls_data = ConstructTlsVector();
+  DCHECK_GT(slot_, 0);
+  DCHECK_LT(slot_, kThreadLocalStorageSize);
+  return tls_data[slot_];
+}
+
+void ThreadLocalStorage::StaticSlot::Set(void* value) {
+  void** tls_data = static_cast<void**>(TlsGetValue(g_native_tls_key));
+  if (!tls_data)
+    tls_data = ConstructTlsVector();
+  DCHECK_GT(slot_, 0);
+  DCHECK_LT(slot_, kThreadLocalStorageSize);
+  tls_data[slot_] = value;
+}
 
 }  // namespace base
 
@@ -67,7 +233,7 @@ void NTAPI OnThreadExit(PVOID module, DWORD reason, PVOID reserved) {
   // On XP SP0 & SP1, the DLL_PROCESS_ATTACH is never seen. It is sent on SP2+
   // and on W2K and W2K3. So don't assume it is sent.
   if (DLL_THREAD_DETACH == reason || DLL_PROCESS_DETACH == reason)
-    base::internal::PlatformThreadLocalStorage::OnThreadExit();
+    WinThreadExit();
 }
 
 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are