Revert 241657 "Implement chromium's TLS."

trunk/src/base/threading/thread_local_storage.cc

-// 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