Implement chromium's TLS.

base/threading/thread_local_storage.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/atomicops.h"
 #include "base/logging.h"
 
+using base::internal::PlatformThreadLocalStorage;
 
 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.
+// 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.
-long g_native_tls_key = TLS_OUT_OF_INDEXES;
+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.
-long g_last_used_tls_key = 0;
+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() {
-  if (g_native_tls_key == TLS_OUT_OF_INDEXES) {
-    long value = TlsAlloc();
-    DCHECK(value != TLS_OUT_OF_INDEXES);
+  PlatformThreadLocalStorage::TLSKey key =
+      base::subtle::NoBarrier_Load(&g_native_tls_key);
+  if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES) {
+    CHECK(PlatformThreadLocalStorage::AllocTLS(&key));
 
-    // 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)) {
+    // 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.
-      TlsFree(value);
+      PlatformThreadLocalStorage::FreeTLS(key);
     }
+    key = base::subtle::NoBarrier_Load(&g_native_tls_key);

[jar (doing other things), 2013/12/05 19:53:32]

nit: I think we only need to do this when some other thread set a better key. 
In most cases, we just set the key.

Bottom line: Can't you do this between lines 84 and 85 above?

[michaelbai, 2013/12/05 22:56:15]

Right, it should be between line 84 and 85.

On 2013/12/05 19:53:32, jar wrote:

   }
-  DCHECK(!TlsGetValue(g_native_tls_key));
+  DCHECK(!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.
-  TlsSetValue(g_native_tls_key, stack_allocated_tls_data);
+  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));
-  TlsSetValue(g_native_tls_key, tls_data);
+  PlatformThreadLocalStorage::SetTLSValue(key, tls_data);
   return tls_data;
 }
 
-// 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;
+}  // namespace
 
-  void** tls_data = static_cast<void**>(TlsGetValue(g_native_tls_key));
+namespace base {
+
+namespace internal {
+
+void PlatformThreadLocalStorage::OnThreadExit(void* value) {
+  void** tls_data = static_cast<void**>(value);
+  // |value| is NULL in Windows platform which doesn't support TLS destructor,

[jar (doing other things), 2013/12/05 19:53:32]

Best would be to have the platform specific code figure this out... but if you
have to do it here....

Handling of this should be done in an #if defined(...) region for Windows.

You can then CHECK() that you're not called (for example) on Posix with a null
value.

[michaelbai, 2013/12/05 22:56:15]

I wanted to avoid #if defined(OS_WIN) code here, In Posix, the value can't be
NULL, these code is de facto Windows specific code; but I don't have strong
feeling about this.

+  // we could get value from TLS key.
+  PlatformThreadLocalStorage::TLSKey key =
+      base::subtle::NoBarrier_Load(&g_native_tls_key);
+  if (!tls_data) {
+    if (key == PlatformThreadLocalStorage::TLS_KEY_OUT_OF_INDEXES)
+      return;
+
+    tls_data = static_cast<void**>(GetTLSValue(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);
+  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).
-    for (int slot = g_last_used_tls_key; slot > 0; --slot) {
+    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.
-  TlsSetValue(g_native_tls_key, NULL);
+  PlatformThreadLocalStorage::SetTLSValue(key, NULL);
 }
 
-}  // namespace
+}  // namespace internal
 
-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))
+  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_ = InterlockedIncrement(&g_last_used_tls_key);
+  slot_ = base::subtle::NoBarrier_AtomicIncrement(&g_last_used_tls_key, 1);
   DCHECK_GT(slot_, 0);
   if (slot_ >= kThreadLocalStorageSize) {

[jar (doing other things), 2013/12/05 19:53:32]

Can you change this to a:
CHECK_LT(slot_, kThreadLocalStorageSize);

We really want to crash when we've exceeded this limit.

[michaelbai, 2013/12/05 22:56:15]

Done.

     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));
+  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**>(TlsGetValue(g_native_tls_key));
+  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
-
-// 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.
-
-// Force a reference to _tls_used to make the linker create the TLS directory
-// if it's not already there.  (e.g. if __declspec(thread) is not used).
-// Force a reference to p_thread_callback_base to prevent whole program
-// optimization from discarding the variable.
-#ifdef _WIN64
-
-#pragma comment(linker, "/INCLUDE:_tls_used")
-#pragma comment(linker, "/INCLUDE:p_thread_callback_base")
-
-#else  // _WIN64
-
-#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)
-    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.
-//
-// See VC\crt\src\tlssup.c for reference.
-
-// extern "C" suppresses C++ name mangling so we know the symbol name for the
-// linker /INCLUDE:symbol pragma above.
-extern "C" {
-// The linker must not discard p_thread_callback_base.  (We force a reference
-// to this variable with a linker /INCLUDE:symbol pragma to ensure that.) If
-// this variable is discarded, the OnThreadExit function will never be called.
-#ifdef _WIN64
-
-// .CRT section is merged with .rdata on x64 so it must be constant data.
-#pragma const_seg(".CRT$XLB")
-// When defining a const variable, it must have external linkage to be sure the
-// linker doesn't discard it.
-extern const PIMAGE_TLS_CALLBACK p_thread_callback_base;
-const PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
-
-// Reset the default section.
-#pragma const_seg()
-
-#else  // _WIN64
-
-#pragma data_seg(".CRT$XLB")
-PIMAGE_TLS_CALLBACK p_thread_callback_base = OnThreadExit;
-
-// Reset the default section.
-#pragma data_seg()
-
-#endif  // _WIN64
-}  // extern "C"