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rocksdb/util/thread_local.cc

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13 KiB

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "util/thread_local.h"
#include "util/mutexlock.h"
#include "port/likely.h"
#include <stdlib.h>
namespace rocksdb {
#if ROCKSDB_SUPPORT_THREAD_LOCAL
__thread ThreadLocalPtr::ThreadData* ThreadLocalPtr::StaticMeta::tls_ = nullptr;
#endif
// 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.
// See http://www.codeproject.com/Articles/8113/Thread-Local-Storage-The-C-Way
// and http://www.nynaeve.net/?p=183
//
// really we do this to have clear conscience since using TLS with thread-pools
// is iffy
// although OK within a request. But otherwise, threads have no identity in its
// modern use.
// This runs on windows only called from the System Loader
#ifdef OS_WIN
// Windows cleanup routine is invoked from a System Loader with a different
// signature so we can not directly hookup the original OnThreadExit which is
// private member
// so we make StaticMeta class share with the us the address of the function so
// we can invoke it.
namespace wintlscleanup {
// This is set to OnThreadExit in StaticMeta singleton constructor
UnrefHandler thread_local_inclass_routine = nullptr;
pthread_key_t thread_local_key = -1;
// Static callback function to call with each thread termination.
void NTAPI WinOnThreadExit(PVOID module, DWORD reason, PVOID reserved) {
// We decided to punt on PROCESS_EXIT
if (DLL_THREAD_DETACH == reason) {
if (thread_local_key != -1 && thread_local_inclass_routine != nullptr) {
void* tls = pthread_getspecific(thread_local_key);
if (tls != nullptr) {
thread_local_inclass_routine(tls);
}
}
}
}
} // wintlscleanup
#ifdef _WIN64
#pragma comment(linker, "/include:_tls_used")
#pragma comment(linker, "/include:p_thread_callback_on_exit")
#else // _WIN64
#pragma comment(linker, "/INCLUDE:__tls_used")
#pragma comment(linker, "/INCLUDE:_p_thread_callback_on_exit")
#endif // _WIN64
// 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 thread_callback_on_exit. (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$XLB")
// When defining a const variable, it must have external linkage to be sure the
// linker doesn't discard it.
extern const PIMAGE_TLS_CALLBACK p_thread_callback_on_exit;
const PIMAGE_TLS_CALLBACK p_thread_callback_on_exit =
wintlscleanup::WinOnThreadExit;
// Reset the default section.
#pragma const_seg()
#else // _WIN64
#pragma data_seg(".CRT$XLB")
PIMAGE_TLS_CALLBACK p_thread_callback_on_exit = wintlscleanup::WinOnThreadExit;
// Reset the default section.
#pragma data_seg()
#endif // _WIN64
} // extern "C"
#endif // OS_WIN
Simplify thread-local static initialization Summary: The call stack used to look like this during static initialization: #0 0x00000000008032d1 in rocksdb::ThreadLocalPtr::StaticMeta::StaticMeta() (this=0x7ffff683b300) at util/thread_local.cc:172 #1 0x00000000008030a7 in rocksdb::ThreadLocalPtr::Instance() () at util/thread_local.cc:135 #2 0x000000000080310f in rocksdb::ThreadLocalPtr::StaticMeta::Mutex() () at util/thread_local.cc:141 #3 0x0000000000803103 in rocksdb::ThreadLocalPtr::StaticMeta::InitSingletons() () at util/thread_local.cc:139 #4 0x000000000080305d in rocksdb::ThreadLocalPtr::InitSingletons() () at util/thread_local.cc:106 It involves outer/inner classes and the call stacks goes outer->inner->outer->inner, which is too difficult to understand. We can avoid a level of back-and-forth by skipping StaticMeta::InitSingletons(), which doesn't initialize anything beyond what ThreadLocalPtr::Instance() already initializes. Now the call stack looks like this during static initialization: #0 0x00000000008032c5 in rocksdb::ThreadLocalPtr::StaticMeta::StaticMeta() (this=0x7ffff683b300) at util/thread_local.cc:170 #1 0x00000000008030a7 in rocksdb::ThreadLocalPtr::Instance() () at util/thread_local.cc:135 #2 0x000000000080305d in rocksdb::ThreadLocalPtr::InitSingletons() () at util/thread_local.cc:106 Test Plan: unit tests verify StaticMeta::mutex_ is still initialized in DefaultEnv() (StaticMeta::mutex_ is the only variable intended to be initialized via StaticMeta::InitSingletons() which I removed) #0 0x00000000005cee17 in rocksdb::port::Mutex::Mutex(bool) (this=0x7ffff69500b0, adaptive=false) at port/port_posix.cc:52 #1 0x0000000000769cf8 in rocksdb::ThreadLocalPtr::StaticMeta::StaticMeta() (this=0x7ffff6950000) at util/thread_local.cc:168 #2 0x0000000000769a53 in rocksdb::ThreadLocalPtr::Instance() () at util/thread_local.cc:133 #3 0x0000000000769a09 in rocksdb::ThreadLocalPtr::InitSingletons() () at util/thread_local.cc:105 #4 0x0000000000647d98 in rocksdb::Env::Default() () at util/env_posix.cc:845 Reviewers: lightmark, yhchiang, sdong Reviewed By: sdong Subscribers: arahut, IslamAbdelRahman, yiwu, andrewkr, dhruba, leveldb Differential Revision: https://reviews.facebook.net/D60813
8 years ago
void ThreadLocalPtr::InitSingletons() { ThreadLocalPtr::Instance(); }
ThreadLocalPtr::StaticMeta* ThreadLocalPtr::Instance() {
// Here we prefer function static variable instead of global
// static variable as function static variable is initialized
// when the function is first call. As a result, we can properly
// control their construction order by properly preparing their
// first function call.
//
// Note that here we decide to make "inst" a static pointer w/o deleting
// it at the end instead of a static variable. This is to avoid the following
// destruction order desester happens when a child thread using ThreadLocalPtr
// dies AFTER the main thread dies: When a child thread happens to use
// ThreadLocalPtr, it will try to delete its thread-local data on its
// OnThreadExit when the child thread dies. However, OnThreadExit depends
// on the following variable. As a result, if the main thread dies before any
// child thread happen to use ThreadLocalPtr dies, then the destruction of
// the following variable will go first, then OnThreadExit, therefore causing
// invalid access.
//
// The above problem can be solved by using thread_local to store tls_ instead
// of using __thread. The major difference between thread_local and __thread
// is that thread_local supports dynamic construction and destruction of
// non-primitive typed variables. As a result, we can guarantee the
// desturction order even when the main thread dies before any child threads.
// However, thread_local requires gcc 4.8 and is not supported in all the
// compilers that accepts -std=c++11 (e.g., the default clang on Mac), while
// the current RocksDB still accept gcc 4.7.
static ThreadLocalPtr::StaticMeta* inst = new ThreadLocalPtr::StaticMeta();
return inst;
}
port::Mutex* ThreadLocalPtr::StaticMeta::Mutex() { return &Instance()->mutex_; }
void ThreadLocalPtr::StaticMeta::OnThreadExit(void* ptr) {
auto* tls = static_cast<ThreadData*>(ptr);
assert(tls != nullptr);
// Use the cached StaticMeta::Instance() instead of directly calling
// the variable inside StaticMeta::Instance() might already go out of
// scope here in case this OnThreadExit is called after the main thread
// dies.
auto* inst = tls->inst;
pthread_setspecific(inst->pthread_key_, nullptr);
MutexLock l(inst->MemberMutex());
inst->RemoveThreadData(tls);
// Unref stored pointers of current thread from all instances
uint32_t id = 0;
for (auto& e : tls->entries) {
void* raw = e.ptr.load();
if (raw != nullptr) {
auto unref = inst->GetHandler(id);
if (unref != nullptr) {
unref(raw);
}
}
++id;
}
// Delete thread local structure no matter if it is Mac platform
delete tls;
}
ThreadLocalPtr::StaticMeta::StaticMeta() : next_instance_id_(0), head_(this) {
if (pthread_key_create(&pthread_key_, &OnThreadExit) != 0) {
abort();
}
// OnThreadExit is not getting called on the main thread.
// Call through the static destructor mechanism to avoid memory leak.
//
// Caveats: ~A() will be invoked _after_ ~StaticMeta for the global
// singleton (destructors are invoked in reverse order of constructor
// _completion_); the latter must not mutate internal members. This
// cleanup mechanism inherently relies on use-after-release of the
// StaticMeta, and is brittle with respect to compiler-specific handling
// of memory backing destructed statically-scoped objects. Perhaps
// registering with atexit(3) would be more robust.
//
// This is not required on Windows.
#if !defined(OS_WIN)
static struct A {
~A() {
#if !(ROCKSDB_SUPPORT_THREAD_LOCAL)
ThreadData* tls_ =
static_cast<ThreadData*>(pthread_getspecific(Instance()->pthread_key_));
#endif
if (tls_) {
OnThreadExit(tls_);
}
}
} a;
#endif // !defined(OS_WIN)
head_.next = &head_;
head_.prev = &head_;
#ifdef OS_WIN
// Share with Windows its cleanup routine and the key
wintlscleanup::thread_local_inclass_routine = OnThreadExit;
wintlscleanup::thread_local_key = pthread_key_;
#endif
}
void ThreadLocalPtr::StaticMeta::AddThreadData(ThreadLocalPtr::ThreadData* d) {
Mutex()->AssertHeld();
d->next = &head_;
d->prev = head_.prev;
head_.prev->next = d;
head_.prev = d;
}
void ThreadLocalPtr::StaticMeta::RemoveThreadData(
ThreadLocalPtr::ThreadData* d) {
Mutex()->AssertHeld();
d->next->prev = d->prev;
d->prev->next = d->next;
d->next = d->prev = d;
}
ThreadLocalPtr::ThreadData* ThreadLocalPtr::StaticMeta::GetThreadLocal() {
#if !(ROCKSDB_SUPPORT_THREAD_LOCAL)
// Make this local variable name look like a member variable so that we
// can share all the code below
ThreadData* tls_ =
static_cast<ThreadData*>(pthread_getspecific(Instance()->pthread_key_));
#endif
if (UNLIKELY(tls_ == nullptr)) {
auto* inst = Instance();
tls_ = new ThreadData(inst);
{
// Register it in the global chain, needs to be done before thread exit
// handler registration
MutexLock l(Mutex());
inst->AddThreadData(tls_);
}
// Even it is not OS_MACOSX, need to register value for pthread_key_ so that
// its exit handler will be triggered.
if (pthread_setspecific(inst->pthread_key_, tls_) != 0) {
{
MutexLock l(Mutex());
inst->RemoveThreadData(tls_);
}
delete tls_;
abort();
}
}
return tls_;
}
void* ThreadLocalPtr::StaticMeta::Get(uint32_t id) const {
auto* tls = GetThreadLocal();
if (UNLIKELY(id >= tls->entries.size())) {
return nullptr;
}
return tls->entries[id].ptr.load(std::memory_order_acquire);
}
void ThreadLocalPtr::StaticMeta::Reset(uint32_t id, void* ptr) {
auto* tls = GetThreadLocal();
if (UNLIKELY(id >= tls->entries.size())) {
// Need mutex to protect entries access within ReclaimId
MutexLock l(Mutex());
tls->entries.resize(id + 1);
}
tls->entries[id].ptr.store(ptr, std::memory_order_release);
}
void* ThreadLocalPtr::StaticMeta::Swap(uint32_t id, void* ptr) {
auto* tls = GetThreadLocal();
if (UNLIKELY(id >= tls->entries.size())) {
// Need mutex to protect entries access within ReclaimId
MutexLock l(Mutex());
tls->entries.resize(id + 1);
}
return tls->entries[id].ptr.exchange(ptr, std::memory_order_acquire);
}
bool ThreadLocalPtr::StaticMeta::CompareAndSwap(uint32_t id, void* ptr,
void*& expected) {
auto* tls = GetThreadLocal();
if (UNLIKELY(id >= tls->entries.size())) {
// Need mutex to protect entries access within ReclaimId
MutexLock l(Mutex());
tls->entries.resize(id + 1);
}
return tls->entries[id].ptr.compare_exchange_strong(
expected, ptr, std::memory_order_release, std::memory_order_relaxed);
}
void ThreadLocalPtr::StaticMeta::Scrape(uint32_t id, autovector<void*>* ptrs,
void* const replacement) {
MutexLock l(Mutex());
for (ThreadData* t = head_.next; t != &head_; t = t->next) {
if (id < t->entries.size()) {
void* ptr =
t->entries[id].ptr.exchange(replacement, std::memory_order_acquire);
if (ptr != nullptr) {
ptrs->push_back(ptr);
}
}
}
}
void ThreadLocalPtr::StaticMeta::Fold(uint32_t id, FoldFunc func, void* res) {
MutexLock l(Mutex());
for (ThreadData* t = head_.next; t != &head_; t = t->next) {
if (id < t->entries.size()) {
void* ptr = t->entries[id].ptr.load();
if (ptr != nullptr) {
func(ptr, res);
}
}
}
}
void ThreadLocalPtr::StaticMeta::SetHandler(uint32_t id, UnrefHandler handler) {
MutexLock l(Mutex());
handler_map_[id] = handler;
}
UnrefHandler ThreadLocalPtr::StaticMeta::GetHandler(uint32_t id) {
Mutex()->AssertHeld();
auto iter = handler_map_.find(id);
if (iter == handler_map_.end()) {
return nullptr;
}
return iter->second;
}
uint32_t ThreadLocalPtr::StaticMeta::GetId() {
MutexLock l(Mutex());
if (free_instance_ids_.empty()) {
return next_instance_id_++;
}
uint32_t id = free_instance_ids_.back();
free_instance_ids_.pop_back();
return id;
}
uint32_t ThreadLocalPtr::StaticMeta::PeekId() const {
MutexLock l(Mutex());
if (!free_instance_ids_.empty()) {
return free_instance_ids_.back();
}
return next_instance_id_;
}
void ThreadLocalPtr::StaticMeta::ReclaimId(uint32_t id) {
// This id is not used, go through all thread local data and release
// corresponding value
MutexLock l(Mutex());
auto unref = GetHandler(id);
for (ThreadData* t = head_.next; t != &head_; t = t->next) {
if (id < t->entries.size()) {
void* ptr = t->entries[id].ptr.exchange(nullptr);
if (ptr != nullptr && unref != nullptr) {
unref(ptr);
}
}
}
handler_map_[id] = nullptr;
free_instance_ids_.push_back(id);
}
ThreadLocalPtr::ThreadLocalPtr(UnrefHandler handler)
: id_(Instance()->GetId()) {
if (handler != nullptr) {
Instance()->SetHandler(id_, handler);
}
}
ThreadLocalPtr::~ThreadLocalPtr() {
Instance()->ReclaimId(id_);
}
void* ThreadLocalPtr::Get() const {
return Instance()->Get(id_);
}
void ThreadLocalPtr::Reset(void* ptr) {
Instance()->Reset(id_, ptr);
}
void* ThreadLocalPtr::Swap(void* ptr) {
return Instance()->Swap(id_, ptr);
}
bool ThreadLocalPtr::CompareAndSwap(void* ptr, void*& expected) {
return Instance()->CompareAndSwap(id_, ptr, expected);
}
void ThreadLocalPtr::Scrape(autovector<void*>* ptrs, void* const replacement) {
Instance()->Scrape(id_, ptrs, replacement);
}
void ThreadLocalPtr::Fold(FoldFunc func, void* res) {
Instance()->Fold(id_, func, res);
}
} // namespace rocksdb