Chris@64: // Copyright (c) 2014, Jason Choy Chris@64: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors Chris@64: // Licensed under the MIT License: Chris@64: // Chris@64: // Permission is hereby granted, free of charge, to any person obtaining a copy Chris@64: // of this software and associated documentation files (the "Software"), to deal Chris@64: // in the Software without restriction, including without limitation the rights Chris@64: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell Chris@64: // copies of the Software, and to permit persons to whom the Software is Chris@64: // furnished to do so, subject to the following conditions: Chris@64: // Chris@64: // The above copyright notice and this permission notice shall be included in Chris@64: // all copies or substantial portions of the Software. Chris@64: // Chris@64: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR Chris@64: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, Chris@64: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE Chris@64: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER Chris@64: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, Chris@64: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN Chris@64: // THE SOFTWARE. Chris@64: Chris@64: #ifndef KJ_THREADLOCAL_H_ Chris@64: #define KJ_THREADLOCAL_H_ Chris@64: Chris@64: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS Chris@64: #pragma GCC system_header Chris@64: #endif Chris@64: // This file declares a macro `KJ_THREADLOCAL_PTR` for declaring thread-local pointer-typed Chris@64: // variables. Use like: Chris@64: // KJ_THREADLOCAL_PTR(MyType) foo = nullptr; Chris@64: // This is equivalent to: Chris@64: // thread_local MyType* foo = nullptr; Chris@64: // This can only be used at the global scope. Chris@64: // Chris@64: // AVOID USING THIS. Use of thread-locals is discouraged because they often have many of the same Chris@64: // properties as singletons: http://www.object-oriented-security.org/lets-argue/singletons Chris@64: // Chris@64: // Also, thread-locals tend to be hostile to event-driven code, which can be particularly Chris@64: // surprising when using fibers (all fibers in the same thread will share the same threadlocals, Chris@64: // even though they do not share a stack). Chris@64: // Chris@64: // That said, thread-locals are sometimes needed for runtime logistics in the KJ framework. For Chris@64: // example, the current exception callback and current EventLoop are stored as thread-local Chris@64: // pointers. Since KJ only ever needs to store pointers, not values, we avoid the question of Chris@64: // whether these values' destructors need to be run, and we avoid the need for heap allocation. Chris@64: Chris@64: #include "common.h" Chris@64: Chris@64: #if !defined(KJ_USE_PTHREAD_THREADLOCAL) && defined(__APPLE__) Chris@64: #include "TargetConditionals.h" Chris@64: #if TARGET_OS_IPHONE Chris@64: // iOS apparently does not support __thread (nor C++11 thread_local). Chris@64: #define KJ_USE_PTHREAD_TLS 1 Chris@64: #endif Chris@64: #endif Chris@64: Chris@64: #if KJ_USE_PTHREAD_TLS Chris@64: #include Chris@64: #endif Chris@64: Chris@64: namespace kj { Chris@64: Chris@64: #if KJ_USE_PTHREAD_TLS Chris@64: // If __thread is unavailable, we'll fall back to pthreads. Chris@64: Chris@64: #define KJ_THREADLOCAL_PTR(type) \ Chris@64: namespace { struct KJ_UNIQUE_NAME(_kj_TlpTag); } \ Chris@64: static ::kj::_::ThreadLocalPtr< type, KJ_UNIQUE_NAME(_kj_TlpTag)> Chris@64: // Hack: In order to ensure each thread-local results in a unique template instance, we declare Chris@64: // a one-off dummy type to use as the second type parameter. Chris@64: Chris@64: namespace _ { // private Chris@64: Chris@64: template Chris@64: class ThreadLocalPtr { Chris@64: // Hacky type to emulate __thread T*. We need a separate instance of the ThreadLocalPtr template Chris@64: // for every thread-local variable, because we don't want to require a global constructor, and in Chris@64: // order to initialize the TLS on first use we need to use a local static variable (in getKey()). Chris@64: // Each template instance will get a separate such local static variable, fulfilling our need. Chris@64: Chris@64: public: Chris@64: ThreadLocalPtr() = default; Chris@64: constexpr ThreadLocalPtr(decltype(nullptr)) {} Chris@64: // Allow initialization to nullptr without a global constructor. Chris@64: Chris@64: inline ThreadLocalPtr& operator=(T* val) { Chris@64: pthread_setspecific(getKey(), val); Chris@64: return *this; Chris@64: } Chris@64: Chris@64: inline operator T*() const { Chris@64: return get(); Chris@64: } Chris@64: Chris@64: inline T& operator*() const { Chris@64: return *get(); Chris@64: } Chris@64: Chris@64: inline T* operator->() const { Chris@64: return get(); Chris@64: } Chris@64: Chris@64: private: Chris@64: inline T* get() const { Chris@64: return reinterpret_cast(pthread_getspecific(getKey())); Chris@64: } Chris@64: Chris@64: inline static pthread_key_t getKey() { Chris@64: static pthread_key_t key = createKey(); Chris@64: return key; Chris@64: } Chris@64: Chris@64: static pthread_key_t createKey() { Chris@64: pthread_key_t key; Chris@64: pthread_key_create(&key, 0); Chris@64: return key; Chris@64: } Chris@64: }; Chris@64: Chris@64: } // namespace _ (private) Chris@64: Chris@64: #elif __GNUC__ Chris@64: Chris@64: #define KJ_THREADLOCAL_PTR(type) static __thread type* Chris@64: // GCC's __thread is lighter-weight than thread_local and is good enough for our purposes. Chris@64: Chris@64: #else Chris@64: Chris@64: #define KJ_THREADLOCAL_PTR(type) static thread_local type* Chris@64: Chris@64: #endif // KJ_USE_PTHREAD_TLS Chris@64: Chris@64: } // namespace kj Chris@64: Chris@64: #endif // KJ_THREADLOCAL_H_