Revert 241657 "Implement chromium's TLS."

trunk/src/base/threading/thread_local_storage_win.cc

Index: trunk/src/base/threading/thread_local_storage_win.cc
===================================================================
--- trunk/src/base/threading/thread_local_storage_win.cc	(revision 242548)
+++ trunk/src/base/threading/thread_local_storage_win.cc	(working copy)
@@ -8,35 +8,201 @@
 
 #include "base/logging.h"
 
+
+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);
+
+    // 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);
+    }
+  }
+  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;
+}
+
+// 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 {
 
-namespace internal {
+ThreadLocalStorage::Slot::Slot(TLSDestructorFunc destructor) {
+  initialized_ = false;
+  slot_ = 0;
+  Initialize(destructor);
+}
 
-bool PlatformThreadLocalStorage::AllocTLS(TLSKey* key) {
-  TLSKey value = TlsAlloc();
-  if (value != TLS_OUT_OF_INDEXES) {
-    *key = value;
-    return true;
+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;
   }
-  return false;
+
+  // Setup our destructor.
+  g_tls_destructors[slot_] = destructor;
+  initialized_ = true;
+  return true;
 }
 
-void PlatformThreadLocalStorage::FreeTLS(TLSKey key) {
-  BOOL ret = TlsFree(key);
-  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;
 }
 
-void* PlatformThreadLocalStorage::GetTLSValue(TLSKey key) {
-  return TlsGetValue(key);
+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 PlatformThreadLocalStorage::SetTLSValue(TLSKey key, void* value) {
-  BOOL ret = TlsSetValue(key, value);
-  DCHECK(ret);
+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 internal
-
 }  // namespace base
 
 // Thread Termination Callbacks.
@@ -67,7 +233,7 @@
   // 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