2 * Copyright 2014 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 #ifndef FOLLY_DETAIL_THREADLOCALDETAIL_H_
18 #define FOLLY_DETAIL_THREADLOCALDETAIL_H_
27 #include <glog/logging.h>
29 #include <folly/Foreach.h>
30 #include <folly/Exception.h>
31 #include <folly/Malloc.h>
34 namespace threadlocal_detail {
37 * Base class for deleters.
41 virtual ~DeleterBase() { }
42 virtual void dispose(void* ptr, TLPDestructionMode mode) const = 0;
46 * Simple deleter class that calls delete on the passed-in pointer.
49 class SimpleDeleter : public DeleterBase {
51 virtual void dispose(void* ptr, TLPDestructionMode mode) const {
52 delete static_cast<Ptr>(ptr);
57 * Custom deleter that calls a given callable.
59 template <class Ptr, class Deleter>
60 class CustomDeleter : public DeleterBase {
62 explicit CustomDeleter(Deleter d) : deleter_(d) { }
63 virtual void dispose(void* ptr, TLPDestructionMode mode) const {
64 deleter_(static_cast<Ptr>(ptr), mode);
72 * POD wrapper around an element (a void*) and an associated deleter.
73 * This must be POD, as we memset() it to 0 and memcpy() it around.
75 struct ElementWrapper {
76 bool dispose(TLPDestructionMode mode) {
81 DCHECK(deleter != nullptr);
82 deleter->dispose(ptr, mode);
99 DCHECK(ptr == nullptr);
100 DCHECK(deleter == nullptr);
103 // We leak a single object here but that is ok. If we used an
104 // object directly, there is a chance that the destructor will be
105 // called on that static object before any of the ElementWrappers
106 // are disposed and that isn't so nice.
107 static auto d = new SimpleDeleter<Ptr>();
114 template <class Ptr, class Deleter>
115 void set(Ptr p, Deleter d) {
116 DCHECK(ptr == nullptr);
117 DCHECK(deleter == nullptr);
120 deleter = new CustomDeleter<Ptr,Deleter>(d);
135 DeleterBase* deleter;
140 * Per-thread entry. Each thread using a StaticMeta object has one.
141 * This is written from the owning thread only (under the lock), read
142 * from the owning thread (no lock necessary), and read from other threads
146 ElementWrapper* elements;
147 size_t elementsCapacity;
152 // Held in a singleton to track our global instances.
153 // We have one of these per "Tag", by default one for the whole system
156 // Creating and destroying ThreadLocalPtr objects, as well as thread exit
157 // for threads that use ThreadLocalPtr objects collide on a lock inside
158 // StaticMeta; you can specify multiple Tag types to break that lock.
161 static StaticMeta<Tag>& instance() {
162 // Leak it on exit, there's only one per process and we don't have to
163 // worry about synchronization with exiting threads.
164 static bool constructed = (inst_ = new StaticMeta<Tag>());
165 (void)constructed; // suppress unused warning
170 std::vector<int> freeIds_;
172 pthread_key_t pthreadKey_;
175 void push_back(ThreadEntry* t) {
177 t->prev = head_.prev;
178 head_.prev->next = t;
182 void erase(ThreadEntry* t) {
183 t->next->prev = t->prev;
184 t->prev->next = t->next;
185 t->next = t->prev = t;
189 static FOLLY_TLS ThreadEntry threadEntry_;
191 static StaticMeta<Tag>* inst_;
193 StaticMeta() : nextId_(1) {
194 head_.next = head_.prev = &head_;
195 int ret = pthread_key_create(&pthreadKey_, &onThreadExit);
196 checkPosixError(ret, "pthread_key_create failed");
198 // pthread_atfork is not part of the Android NDK at least as of n9d. If
199 // something is trying to call native fork() directly at all with Android's
200 // process management model, this is probably the least of the problems.
202 ret = pthread_atfork(/*prepare*/ &StaticMeta::preFork,
203 /*parent*/ &StaticMeta::onForkParent,
204 /*child*/ &StaticMeta::onForkChild);
205 checkPosixError(ret, "pthread_atfork failed");
209 LOG(FATAL) << "StaticMeta lives forever!";
212 static ThreadEntry* getThreadEntry() {
214 return &threadEntry_;
216 ThreadEntry* threadEntry =
217 static_cast<ThreadEntry*>(pthread_getspecific(inst_->pthreadKey_));
219 threadEntry = new ThreadEntry();
220 int ret = pthread_setspecific(inst_->pthreadKey_, threadEntry);
221 checkPosixError(ret, "pthread_setspecific failed");
227 static void preFork(void) {
228 instance().lock_.lock(); // Make sure it's created
231 static void onForkParent(void) {
232 inst_->lock_.unlock();
235 static void onForkChild(void) {
236 // only the current thread survives
237 inst_->head_.next = inst_->head_.prev = &inst_->head_;
238 ThreadEntry* threadEntry = getThreadEntry();
239 // If this thread was in the list before the fork, add it back.
240 if (threadEntry->elementsCapacity != 0) {
241 inst_->push_back(threadEntry);
243 inst_->lock_.unlock();
246 static void onThreadExit(void* ptr) {
247 auto& meta = instance();
249 ThreadEntry* threadEntry = getThreadEntry();
251 DCHECK_EQ(ptr, &meta);
252 DCHECK_GT(threadEntry->elementsCapacity, 0);
254 ThreadEntry* threadEntry = static_cast<ThreadEntry*>(ptr);
257 std::lock_guard<std::mutex> g(meta.lock_);
258 meta.erase(threadEntry);
259 // No need to hold the lock any longer; the ThreadEntry is private to this
260 // thread now that it's been removed from meta.
262 // NOTE: User-provided deleter / object dtor itself may be using ThreadLocal
263 // with the same Tag, so dispose() calls below may (re)create some of the
264 // elements or even increase elementsCapacity, thus multiple cleanup rounds
266 for (bool shouldRun = true; shouldRun; ) {
268 FOR_EACH_RANGE(i, 0, threadEntry->elementsCapacity) {
269 if (threadEntry->elements[i].dispose(TLPDestructionMode::THIS_THREAD)) {
274 free(threadEntry->elements);
275 threadEntry->elements = nullptr;
276 pthread_setspecific(meta.pthreadKey_, nullptr);
279 // Allocated in getThreadEntry(); free it
284 static int create() {
286 auto & meta = instance();
287 std::lock_guard<std::mutex> g(meta.lock_);
288 if (!meta.freeIds_.empty()) {
289 id = meta.freeIds_.back();
290 meta.freeIds_.pop_back();
297 static void destroy(size_t id) {
299 auto & meta = instance();
300 // Elements in other threads that use this id.
301 std::vector<ElementWrapper> elements;
303 std::lock_guard<std::mutex> g(meta.lock_);
304 for (ThreadEntry* e = meta.head_.next; e != &meta.head_; e = e->next) {
305 if (id < e->elementsCapacity && e->elements[id].ptr) {
306 elements.push_back(e->elements[id]);
309 * Writing another thread's ThreadEntry from here is fine;
310 * the only other potential reader is the owning thread --
311 * from onThreadExit (which grabs the lock, so is properly
312 * synchronized with us) or from get(), which also grabs
313 * the lock if it needs to resize the elements vector.
315 * We can't conflict with reads for a get(id), because
316 * it's illegal to call get on a thread local that's
319 e->elements[id].ptr = nullptr;
320 e->elements[id].deleter = nullptr;
321 e->elements[id].ownsDeleter = false;
324 meta.freeIds_.push_back(id);
326 // Delete elements outside the lock
327 FOR_EACH(it, elements) {
328 it->dispose(TLPDestructionMode::ALL_THREADS);
330 } catch (...) { // Just in case we get a lock error or something anyway...
331 LOG(WARNING) << "Destructor discarding an exception that was thrown.";
336 * Reserve enough space in the ThreadEntry::elements for the item
339 static void reserve(int id) {
340 auto& meta = instance();
341 ThreadEntry* threadEntry = getThreadEntry();
342 size_t prevCapacity = threadEntry->elementsCapacity;
343 // Growth factor < 2, see folly/docs/FBVector.md; + 5 to prevent
345 size_t newCapacity = static_cast<size_t>((id + 5) * 1.7);
346 assert(newCapacity > prevCapacity);
347 ElementWrapper* reallocated = nullptr;
349 // Need to grow. Note that we can't call realloc, as elements is
350 // still linked in meta, so another thread might access invalid memory
351 // after realloc succeeds. We'll copy by hand and update our ThreadEntry
353 if (usingJEMalloc()) {
354 bool success = false;
355 size_t newByteSize = nallocx(newCapacity * sizeof(ElementWrapper), 0);
357 // Try to grow in place.
359 // Note that xallocx(MALLOCX_ZERO) will only zero newly allocated memory,
360 // even if a previous allocation allocated more than we requested.
361 // This is fine; we always use MALLOCX_ZERO with jemalloc and we
362 // always expand our allocation to the real size.
363 if (prevCapacity * sizeof(ElementWrapper) >=
364 jemallocMinInPlaceExpandable) {
365 success = (xallocx(threadEntry->elements, newByteSize, 0, MALLOCX_ZERO)
369 // In-place growth failed.
371 success = ((reallocated = static_cast<ElementWrapper*>(
372 mallocx(newByteSize, MALLOCX_ZERO))) != nullptr);
376 // Expand to real size
377 assert(newByteSize / sizeof(ElementWrapper) >= newCapacity);
378 newCapacity = newByteSize / sizeof(ElementWrapper);
380 throw std::bad_alloc();
382 } else { // no jemalloc
383 // calloc() is simpler than malloc() followed by memset(), and
384 // potentially faster when dealing with a lot of memory, as it can get
385 // already-zeroed pages from the kernel.
386 reallocated = static_cast<ElementWrapper*>(
387 calloc(newCapacity, sizeof(ElementWrapper)));
389 throw std::bad_alloc();
393 // Success, update the entry
395 std::lock_guard<std::mutex> g(meta.lock_);
397 if (prevCapacity == 0) {
398 meta.push_back(threadEntry);
403 * Note: we need to hold the meta lock when copying data out of
404 * the old vector, because some other thread might be
405 * destructing a ThreadLocal and writing to the elements vector
408 memcpy(reallocated, threadEntry->elements,
409 sizeof(ElementWrapper) * prevCapacity);
411 swap(reallocated, threadEntry->elements);
413 threadEntry->elementsCapacity = newCapacity;
419 if (prevCapacity == 0) {
420 pthread_setspecific(meta.pthreadKey_, &meta);
425 static ElementWrapper& get(size_t id) {
426 ThreadEntry* threadEntry = getThreadEntry();
427 if (UNLIKELY(threadEntry->elementsCapacity <= id)) {
429 assert(threadEntry->elementsCapacity > id);
431 return threadEntry->elements[id];
437 FOLLY_TLS ThreadEntry StaticMeta<Tag>::threadEntry_{nullptr, 0,
440 template <class Tag> StaticMeta<Tag>* StaticMeta<Tag>::inst_ = nullptr;
442 } // namespace threadlocal_detail
445 #endif /* FOLLY_DETAIL_THREADLOCALDETAIL_H_ */