Cleanup thread_local_storage on Windows

base/threading/thread_local_storage_win.cc

 // Copyright (c) 2012 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 <windows.h>
 
 #include "base/logging.h"
 
 
-namespace base {
+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.
 
-namespace {
+// 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 ThreadLocalStorage::TLSDestructorFunc
+volatile base::ThreadLocalStorage::TLSDestructorFunc
     g_tls_destructors[kThreadLocalStorageSize];
 
-}  // namespace anonymous
-
-// 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.
-
-// tls_key_ is the one native TLS that we use.  It stores our
-// table.
-long ThreadLocalStorage::tls_key_ = TLS_OUT_OF_INDEXES;
-
-// tls_max_ is the high-water-mark of allocated thread local storage.
-// We intentionally skip 0 so that it is not confused with an
-// unallocated TLS slot.
-long ThreadLocalStorage::tls_max_ = 1;
-
-void** ThreadLocalStorage::Initialize() {
-  if (tls_key_ == TLS_OUT_OF_INDEXES) {
+void** ConstructTlsVector() {
+  if (g_native_tls_key == TLS_OUT_OF_INDEXES) {
     long value = TlsAlloc();
     DCHECK(value != TLS_OUT_OF_INDEXES);
 
     // 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 (InterlockedCompareExchange(&tls_key_, value, TLS_OUT_OF_INDEXES) !=
-            TLS_OUT_OF_INDEXES) {
-      // We've been shortcut. Another thread replaced tls_key_ first so we need
-      // to destroy our index and use the one the other thread got first.
+    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);
     }
   }
-  DCHECK(!TlsGetValue(tls_key_));
+  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(tls_key_, stack_allocated_tls_data);
+  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(tls_key_, tls_data);
+  TlsSetValue(g_native_tls_key, tls_data);
   return tls_data;
 }
 
-ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
-  initialized_ = false;
-  slot_ = 0;
-  Initialize(destructor);
-}
-
-bool ThreadLocalStorage::StaticSlot::Initialize(TLSDestructorFunc destructor) {
-  if (tls_key_ == TLS_OUT_OF_INDEXES || !TlsGetValue(tls_key_))
-    ThreadLocalStorage::Initialize();
-
-  // Grab a new slot.
-  slot_ = InterlockedIncrement(&tls_max_) - 1;
-  DCHECK_GT(slot_, 0);
-  if (slot_ >= kThreadLocalStorageSize) {
-    NOTREACHED();
-    return false;
-  }
-
-  // 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**>(TlsGetValue(tls_key_));
-  if (!tls_data)
-    tls_data = ThreadLocalStorage::Initialize();
-  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(tls_key_));
-  if (!tls_data)
-    tls_data = ThreadLocalStorage::Initialize();
-  DCHECK_GT(slot_, 0);
-  DCHECK_LT(slot_, kThreadLocalStorageSize);
-  tls_data[slot_] = value;
-}
-
-void ThreadLocalStorage::ThreadExit() {
-  if (tls_key_ == TLS_OUT_OF_INDEXES)
+// 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(tls_key_));
+  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(tls_key_, stack_allocated_tls_data);
+  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 = tls_max_ - 1; slot > 0; --slot) {
+    for (int slot = g_last_used_tls_key; slot > 0; --slot) {
       void* value = stack_allocated_tls_data[slot];
       if (value == NULL)
         continue;
-      TLSDestructorFunc destructor = g_tls_destructors[slot];
+      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(tls_key_, NULL);
+  TlsSetValue(g_native_tls_key, NULL);
+}
+
+}  // namespace
+
+namespace base {
+
+ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
+  initialized_ = false;
+  slot_ = 0;
+  Initialize(destructor);
+}
+
+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 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**>(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
 
 // Thread Termination Callbacks.
 // Windows doesn't support a per-thread destructor with its
 // TLS primitives.  So, we build it manually by inserting a
 // function to be called on each thread's exit.
 // This magic is from http://www.codeproject.com/threads/tls.asp
 // and it works for VC++ 7.0 and later.
@@ skipping 12 matching lines @@
 #pragma comment(linker, "/INCLUDE:__tls_used")
 #pragma comment(linker, "/INCLUDE:_p_thread_callback_base")
 
 #endif  // _WIN64
 
 // Static callback function to call with each thread termination.
 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::ThreadLocalStorage::ThreadExit();
+    WinThreadExit();
 }
 
 // .CRT$XLA to .CRT$XLZ is an array of PIMAGE_TLS_CALLBACK pointers that are
 // called automatically by the OS loader code (not the CRT) when the module is
 // loaded and on thread creation. They are NOT called if the module has been
 // loaded by a LoadLibrary() call. It must have implicitly been loaded at
 // process startup.
 // By implicitly loaded, I mean that it is directly referenced by the main EXE
 // or by one of its dependent DLLs. Delay-loaded DLL doesn't count as being
 // implicitly loaded.
@@ skipping 21 matching lines @@
 #else  // _WIN64
 
 #pragma data_seg(".CRT$XLB")
 PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
 
 // Reset the default section.
 #pragma data_seg()
 
 #endif  // _WIN64
 }  // extern "C"