| // 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 { |
| // 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 { |
| |
| 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. |
| |
| // 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" |